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授 课 教 案
环境生态学
课程名称：
总 学 时：
课程类别：
30
总 学 分：
选修
任课教师：
黄河
单
位：
化工学院
职
称：
副教授
授课专业：
授课班级：
2
环境工程
环工 11201，环工 11202
2014 ～2015 学年
第
一
学期
1
课
题
1.Introduction
学
时
2
理解生态学概念，明确学习生态学的目的，了解生态学的研究内容。
教学目标
与要求
理解生态学概念
重
点
理解生态学概念
难
点
讲授、讨论、多媒体
教学方法
与手段
1、The economy of nature，6 th ed，Robert E. Ricklefs，2008 by W. H. Freeman and
Company；
2. General Ecology, 2th ed., David T. Krohne. Thomson Learning, Inc. ISBN
0-534-37528-6;
3. Ecology : Concepts and Applications 4th ed McGraw-Hill Companies, Inc. ;
4. Ecology :From Individuals to Ecosystems,4th ed published 2006, Blackwell
参考资料
Publishing;；
5.孙儒泳，李庆芬，牛翠娟，娄安如. 2002. 基础生态学. 高等教育出版社；
6.孙儒泳，李博，诸葛阳，尚玉昌编. 1992. 普通生态学. 高等教育出版社；
7. 李博主编. 1999. 生态学. 高等教育出版社；
8. 盛连喜主编，2005，
《环境生态学导论》，高等教育出版社。
2
教学内容及过程
0.1 What is ecology?
0.2 Why do we need to study Ecology?
0.3 How to study ecology?
0.4 The nature of Ecology
0.1 What is Ecology?
By ecology, we mean the body of knowledge concerning the economy of nature -- the
investigation of the total relations of the animal both to its organic and to its inorganic
environment; including above all, its friendly and inimical relation with those animals and
plants with which it comes directly or indirectly into contact -- in a word, ecology is the study
of all the complex interrelationships referred to by Darwin as the conditions of the struggle for
existence. Ernst Haeckel, 1870.
So, what is ecology?
Ecology is the science by which we study how organisms (animals, plants, and microbes)
interact in and with the natural world. Please note the important key words in the above
definition!
Ecology - A Science for Today
We have a great need for ecological understanding:
what are the best policies for managing our environmental support systems -- our watersheds,
agricultural lands, wetlands?
we must apply ecological principles to: solve or prevent environmental problems inform our
economic, political, and social thought and practice
Our Objectives...
We are on the road to ecological thinking:
we’ll have many vantage points of varying complexity
we’ll understand ecological systems and the interdependence of their components
we’ll establish a core of principles regarding:
physical and chemical attributes regulation of structure and function, evolutionary change,
Ecological Systems Large and Small:
Organism (“No smaller unit in biology ... has a separate life in the environment...”)
Population (many organisms of the same kind living together)
Guild (a group of populations that utilizes resources in essentially the same way)
Community (many populations of different kinds living in the same place)
Ecosystem (assemblages of organisms together with their physical environment)
Biosphere (the global ecosystem, all organisms and environments on earth)
Perspectives of Ecologists: Organism Approach
How do form, physiology, and behavior lead to survival?
Focus is on adaptations, modifications of structure and function, that suit the organism for life
in its environment: adaptations result from evolutionary change by natural selection, a natural
link to population approach...
Perspectives of Ecologists: Population Approach
备注栏
注：用于
举例、案
例以及
新增内
容等的
书写。
3
What determines the numbers of individuals and their variations in time and space?
Focus is on processes of birth and death, immigration and emigration,influenced by: the
physical environment evolutionary processes interactions with other populations, a natural
link to community approach...
Perspectives of Ecologists: Community Approach
How are communities structured from their component populations?
Focus is on the diversity and relative abundance of different kinds of organisms living
together, affected by: population interactions, promoting and limiting coexistence feeding
relationships, responsible for fluxes of energy and materials, a natural link to ecosystem
approach...
Perspectives of Ecologists: Ecosystem Approach
How can we account for the activities of populations in the common “currencies” of energy
and materials?
Focus is on movements of energy and materials and influences of: organisms large and small
climate and other physical factors, including those acting on a global scale,a natural link to
biosphere approach...
Perspectives of Ecologists: Biosphere Approach
How can we understand the global movements of air and water, and the energy and chemical
elements they contain?
Focus is on the global circulation of matter and energy, affecting: distributions of
organisms ,changes in populations ,composition of communities , productivity of ecosystems
Kinds of Organisms and Their Ecological Roles
Characteristics of ecosystems depend on varied forms of life:
plants and animals are conspicuous and important, but no more so than more primitive forms,
like the bacteria, which dominated much of earth’s early history, making it possible for their
more complex escendents to survive!
Plants use energy in sunlight to produce organic matter.
Plants capture the energy of sunlight and transform it into chemical form. Plants must use
external surfaces for absorbing light and exchanging gases,water, and nutrients.
Plants stay closely attached to their sources of water, from soil, atmosphere,or bodies of water.
Animals feed on other organisms or their remains.
Animals depend on organic foods ultimately produced by plants.
Animals can use internal surfaces for exchange of gases, nutrients, and water. Animals can
assume streamlined shapes, with other systems permitting motility. Animals can be less directly
tied to sources of water than plants.
Fungi are highly effective decomposers.
Fungi assume unique roles in ecosystems because of their distinctive form. Fungi penetrate
dead materials effectively, making nutrients available to others. Fungi digest externally, and
capture inorganic nutrients and water from soils.
Protists are single-celled ancestors of more complex life forms.
Protists are highly diverse single-celled forms, including algae, slime molds, and protozoa.
Protists lack specialized tissues and organs, yet fill almost every ecological role:
photosynthetic organisms ❙ grazers and predators❙ decomposers
4
Bacteria have a wide variety of biochemical mechanisms for energy transformations.
Bacteria consist of simple, single cells lacking nuclei and chromosomes. Bacteria are
biochemical specialists, accomplishing unique transformations:
nitrogen fixation chemoautotrophic production metabolism under anaerobic conditions
Organisms cooperate in nature.
Many types of organisms live together in close association, forming symbioses:
each partner provides something the other lacks examples of symbiotic relationships include:
lichens (fungus and alga)
bacteria fermenting plant material in a cow’s gut beneficial fungi associated with the roots of
plants photosynthetic algae in corals and clams nitrogen-fixing bacteria in root nodules of
legumes
Habitat and Niche
The habitat is a place or physical setting in which an organism lives.
Examples include: forests deserts coral reefs
The habitat is characterized by: conspicuous physical features, dominant plant (or animal) life
Classifying habitats is useful but difficult!
The habitat concept is useful; it emphasizes conditions experienced by organisms.
Classification systems are varied and typically hierarchical:
aquatic habitats (vs. terrestrial)❘ marine habitats (vs. freshwater)
• oceanic habitats (vs. estuarine)– benthic habitats (vs. pelagic)
Finer subdivisions overlap rather broadly!
Niche
❚ The niche of an organism encompasses: ranges of conditions tolerated role in ecological
systems
❚ No two species have the same niche: each has distinctive form and function；No organism
can live under all conditions: each has unique habitat requirements ；each has a unique niche
Systems and Processes: Dimensions in Time and Space
❚ Nothing in nature is static: anything we can measure (conditions, number of organisms)
exhibits variation.
❚ Variation has temporal and spatial components. Variation in each measurement has a
characteristic scale; for the same degree of change:
❙ air temperature varies over hours
❙ ocean temperature varies over weeks or months
Temporal Variation
❚ Consider two kinds of temporal variation:
❙ predictable, cyclic variations (daily, seasonal)
❙ unpredictable, irregular variations
❚ A temporal “rule of thumb”: the more extreme the condition, the less frequent (compare
cold fronts and hurricanes)
❙ but frequency and severity are relative terms that depend on the organism!
5
Spatial Variation
❚ Spatial variation occurs at very small (forest sunflecks) and very large (latitudinal variation
in solar flux) scales.
❚ Scale of variation importance is a function of the organism:
❙ the two sides of a leaf are different to an aphid a moose eats the whole leaf, aphid and all
Time and Space
❚ A few generalizations: moving organisms experience spatial variation as temporal variation
❙ the faster an individual moves: the smaller the scale of spatial variation；the more quickly it
encounters new environments；the shorter the temporal scale of variation
❙ spatial and temporal scales are correlated
❙ frequency is inversely related to extent/severity
Physical and Biological Principles 1
❚ Ecological systems are physical entities:
life builds on physical properties and chemical reactions of matter
❙ all processes obey the physical laws of thermodynamics
❙ but life still pursues many varied options
Physical and Biological Principles 2
❚ Ecological systems exist in dynamic steady states:
❙ despite substantial fluxes of energy and matter, ecological systems remain more or less
unchanged
❙ gains and losses are more or less balanced
❙ steady states apply to fluxes of materials and energy at all levels of
ecological organization
Physical and Biological Principles 3
❚ The maintenance of living systems requires the expenditure of energy:
❙ life forms exist out of equilibrium with their physical environment
❙ losses must be replaced by energy or materials procured by the organism
❙ the price of maintaining a dynamic steady state is energy
Physical and Biological Principles 4
❚ Ecological systems undergo evolutionary change through time:
❙ physical and chemical properties, and physical laws, are immutable, but life exhibits
remarkable diversity
❙ structures and functions of organisms (adaptations) are evolutionary
products of natural selection, recognized by Charles Darwin
❙ complexity builds upon complexity
How Ecologists Study the Natural World
❚ Ecologists, like other scientists, employ a scientific method:
❙ observation and description of natural phenomena
❙ development of hypotheses or explanations
❙ testing the predictions of these hypotheses
❚ We test hypotheses because many explanations are plausible. Which is best?
Ecology Employs the Scientific Method❙
6
What is an hypothesis?
❚ An hypothesis is an idea about how the world works:
❙ e.g., “Frogs sing on warm nights after periods of rain.”
❚ We often wish to understand two components of such a phenomenon:
❙ how? (encompasses physiological processes)
why? (encompasses costs and benefits of the behavior to the individual)
Experiments test predictions.
❚ Hypotheses generate predictions:
❙ if observations confirm the prediction, the hypothesis is strengthened (not proven)
❙ if observations fail to confirm the prediction, the hypothesis is weakened (or rejected)
❚ Best tests of hypotheses are experiments:
❙ independently manipulate one/few variables
❙ establish appropriate controls
Some Potential Pitfalls
❚ A correlation between variables does not establish causation.
❚ Many hypotheses cannot be tested by experimental methods because:
❙ the scale is too large:
❘ patterns may have evolved over long periods
❘ the spatial extent is too large for manipulation
❙ causal factors cannot be independently tested
Some Approaches to Difficult Problems
❚ Microcosms are sometimes useful:
❙ microcosms replicate essential features of the system in a laboratory or field setting
❚ Mathematical models are powerful tools:
❙ researcher portrays system as set of equations
model is an hypothesis and yields predictions that can be tested; examples include:
❘ models of disease spread
models of global carbon
Humans are a prominent part of the biosphere.
Why study ecology?
the wonders of the natural world stimulate our curiosity and our desire to understand our
surroundings
❙ a growing human population increasingly stresses the natural world, causing two related
problems:
❘ impact of humans on natural systems deterioration of our own environment
A Focus on Human Impacts
❚ Human impacts are everywhere...
We are inundated with environmental problems (disappearing tropical forests,ozone hole,
depleted fish stocks, etc.).
❚ Increasingly, the only effective means of preserving natural resources Is through
conservation of entire ecological systems and management of broadscale processes.
Success Stories
Many positive efforts are underway:
❙ cleanup of rivers, lakes, and air
❙ reduction in acid rain
7
reduction in release of chlorofluorocarbons
❙ widespread focus on CO2 and global warming
❙ protection of endangered species international cooperation (IUCN, WWW)
❙ international agreements (CITES, Rio)
Summary 1
Ecology is the scientific study of the natural environment and the relationships
of organisms to one another and to their surroundings.
❚ Ecologists study a variety of organisms and processes, spanning a wide range of spatial and
temporal scales.
❚ Individual organisms live in habitats and have unique niches reflecting
conditions tolerated and functional role.
Summary 2
❚ All ecological systems obey natural laws and are subject to evolutionary change.
❚ Ecologists employ the scientific method.
Humans are part of the global ecosystem and have created numerous
environmental problems. Solving these problems will require application of
ecological principles.
作业布置
0.1 What is ecology?
0.2 Why do we need to study Ecology?
0.3 How to study ecology?
0.4 The nature of Ecology
课后小结
8
课
题
Lecture 2: Adaptation to Physical Environment: Water, light, temperature, and
climate
学
时
6
掌握 Water, light, temperature, and climate 对生物的影响规律
教学目标
与要求
掌握 water 对生物的影响规律
重
点
light and climate 对生物的影响规律
难
点
讲授、讨论、多媒体
教学方法
与手段
1、The economy of nature，6 th ed，Robert E. Ricklefs，2008 by W. H. Freeman and
Company；
2. General
Ecology, 2th ed., David T. Krohne. Thomson Learning, Inc.
ISBN
0-534-37528-6;
3. Ecology : Concepts and Applications 4th ed McGraw-Hill Companies, Inc. ;
参考资料
4. Ecology :From Individuals to Ecosystems,4th ed published 2006, Blackwell
Publishing;；
5.孙儒泳，李庆芬，牛翠娟，娄安如. 2002. 基础生态学. 高等教育出版社；
6.孙儒泳，李博，诸葛阳，尚玉昌编. 1992. 普通生态学. 高等教育出版社；
7. 李博主编. 1999. 生态学. 高等教育出版社；
8. 盛连喜主编，2005，
《环境生态学导论》，高等教育出版社。
9
教学内容及过程
Topics: Water
2.1 Global water cycling
2.2 Water has many properties favorable to life
2.3 Many inorganic nutrients are dissolved in water
2.4 Plants obtain water and nutrients from soil
2.5 Maintain salt and water balance by plants and animals
2.1 Global Hydrologic (water) cycle between Earth and atmosphere Cycle
 Water is essential for life (75-95% weight of living cell)
 Over 75% of the Earth’s surface is covered by water
Oceans contain 97%.
Polar ice caps and glaciers contain 2%.
Freshwater in lakes, streams, and ground water make up less than 1%.
(Saltwater and fresh water)
 The water (or hydrologic) cycle is the process by which water travels in a sequence
from the air to Earth and returns to the atmosphere
 Solar radiation is the driving force behind the water cycle because it provides energy
for the evaporation of water
Water Cycles between Earth and the Atmosphere
 The water (or hydrologic) cycle is the process by which water travels in a sequence
from the air to Earth and returns to the atmosphere
 Solar radiation is the driving force behind the water cycle because it provides energy
for the evaporation of water
2.2 Properties of water that favorable to life
Water has many properties favorable for the maintenance of life.
Water, an ideal life medium:
is abundant over most of earth’s surface
is an excellent solvent and medium for chemical processes
allows for high concentrations of molecules necessary for rapid chemical reactions
enables movements of organisms because of its fluidity
Thermal Properties of Water
❚
Thermal properties:
❙ liquid over broad range of temperatures
❙ conducts heat rapidly
resists temperature changes because of its heat capacity
❙ resists changes in state:
❘ freezing requires heat removal of 80 cal/g
❘ evaporation requires heat addition of over 500 cal/g
10
Water has other remarkable thermal properties.
❚
Most substances become denser as they cool.
❚ Water also becomes denser, to a point, but:
❙ reaches maximum density at 4oC, and expands as it cools below that point expands even
further upon freezing. This property is of monumental importance to life on earth:
❙ bottoms of lakes and oceans prevented from freezing floating layer of ice with covering of
snow forms protective, insulating surface
The Buoyancy and Viscosity of Water
❚ Density of water (800x that of air) means that water is buoyant.
❚ Aquatic organisms achieve neutral density through: reduction (bony fish) or elimination
(sharks) of hard skeletal components
❙ use of gas-filled swim bladder (plants too!)
❙ accumulation of lipids
❚ Water’s viscosity retards the movement of organisms (some organisms are streamlined,
others deploy parachutes).
2.3 Many inorganic nutrients are dissolved in water
All natural waters contain dissolved substances.
❚
Water is a powerful solvent because of its charge polarity.
❚ Almost all substances dissolve to some extent in water. Nearly all water contains some
dissolved substances: rainwater acquires dissolved gasses and trace minerals; lakes and rivers
contain 0.01-0.02% dissolved minerals; oceans contain 3.4% dissolved minerals
Fresh Versus Salt Water
❚
❙
❙
❚
❙
❙
❚
Noteworthy differences in makeup of solutes:
salt water is rich in Na+, Cl-, Mg2+, SO42fresh water is rich in Ca2+, HCO3-, and SO42Solute loads of surface waters reflect bedrock chemistry:
water of limestone areas is “hard” with substantial Ca2+, HCO3water of granitic areas contains few mineral elements
Oceanic waters are saturated with respect to Ca2+, but continue to accumulate Na+.
Waters differ in contents of essential nutrients.
❚
N and P are among most the important essential elements and are often limiting:
❙ typical fresh water N is 0.40 mg/L, while P is about 0.01 mg/L (N>P).
❙ typical salt water N is less than 0.01 mg/L, while P is about 0.01-0.1 mg/L (P>N).
pH - the Concentration of Hydrogen Ions
❚
Normal pH range of surface waters is 6-9.
❚ Acid rain can lower pH to as low as 4 in some areas.
❚ Acidity dissolves minerals❚❙
water in limestone areas is “hard” with substantial Ca2+, HCO3❙ most organisms regulate pH around neutrality; adaptations to life out of balance
with external medium (high or low pH) are costly (it takes energy to be different!)
11
C and O are intimately involved in energy transformations.
Compounds contain energy in their chemical bonds:
energy is required to create bonds
❙ energy is released when bonds are broken
Energy transformations proceed by oxidation and reduction, often involving C:
❙ oxidation removes electrons, releases energy
❙ reduction adds electrons, requiring energy
Heterotrophs and Autotrophs
❚ Heterotrophs obtain their energy by consuming organic (biological) sources of
carbon-rich food, which they oxidize.
Autotrophs obtain their energy from inorganic sources, and use this energy to
reduce carbon, which they store for later use:
❙ photoautotrophs obtain energy from light
❙ chemoautotrophs obtain energy from oxidation of inorganic compounds such as
H2S, NH4+
❚Photosynthesis and Respiration
❚ Think of photosynthesis and respiration as complementary reactions which:
❙ reduce carbon (photosynthesis): energy + 6C
❘ water is an electron donor (reducing agent)
❙
❘ oxygen is an electron acceptor (oxidizing agent)
The Limited Availability of Inorganic Carbon 1
❚ Terrestrial plants have a difficult time acquiring inorganic carbon:
❙ carbon (as CO2) diffuses into leaf from atmosphere:
❘ rate of diffusion of a gas is proportional to concentration difference between
external and internal media
❘ atmosphere-to-plant difference in [CO2] is small
❘ plant-to-atmosphere difference in [H2O] is great
❘ bottom line: plants lose enormous amounts of water to the atmosphere relative
to carbon gained, at a rate of 500 g water for each g of carbon
The Limited Availability of Inorganic Carbon 2
❚ Aquatic plants have a more reliable source of carbon than terrestrial plants. Here’s why:
❙ at typical pH (6-9), solubility of CO2 in water is about 0.03% by volume
❙ carbon is rapidly converted to HCO3this process depletes dissolved CO2, allowing for more CO2 to enter the water,which in turn
further enriches the HCO3- pool, available for plant uptake
Carbon dioxide diffuses slowly through water.
❚ Both CO2 and HCO3- diffuse slowly through water.
❚ A thin boundary layer (10-500 um) adjacent to the plant surface becomes carbon depleted,
and it forms a diffusion barrier between the plant and C-rich water beyond.
Oxygen is scarce in water.
12
❚ Oxygen is rather limited in water:
❙ low solubility limited diffusion
❙ below limit of light penetration and in sediments rich in organic matter, conditions become
anaerobic or anoxic
Availability of Inorganic Nutrients
❚ After H, C, and O, elements required in greatest quantity are N, P, S, K, Ca, Mg, and Fe.
❚ Certain organisms require other elements:
❙ diatoms require Si for their glassy cases
❙ nitrogen-fixing bacteria require Mo as part of the key enzyme in N assimilation
❚ Terrestrial plants acquire most elements from water in soil around roots:
❙ availability varies with temperature, pH, presence of other ions
❙ P is particularly limiting in soils
Topics 2: Light
Light is the primary source of energy for the biosphere.
❚ A quick primer on light:
❙ energy reaching earth from the sun covers a broad spectrum of wavelengths:
❘ visible light ranges from 400 nm (violet) to 700 nm (red)
❘ shorter wavelength energy (<400 nm) is ultraviolet (UV)
❘ longer wavelength energy (>700 nm) is infrared (IR)
❙ energy content of light varies inversely with its wavelength
❘ the shorter the wavelength, the more energetic the light
Ozone and Ultraviolet Radiation
❚ UV “light” has a high energy level and can damage exposed cells and tissues.
❚ Ozone in upper atmosphere absorbs strongly in ultraviolet portion of electromagnetic
spectrum.
Chlorofluorocarbons (formerly used as propellants and refrigerants) react with and chemically
destroy ozone:
❙ ozone “holes” appeared in the atmosphere
❙ concern over this phenomenon led to strict controls on CFCs and other substances depleting
ozone
Infrared Light and the Greenhouse Effect 1
All objects, including the earth’s surface, emit longwave (infrared) radiation (IR).
❚ Atmosphere is transparent to visible light, which warms the earth’s surface.
Infrared Light and the Greenhouse Effect 2
❚ Infrared light (IR) emitted by earth is absorbed in part by atmosphere, which is only partially
transparent to IR.
Substances like carbon dioxide and methane increase the absorptive capacity of the atmosphere
to IR, resulting in atmospheric warming.
Greenhouse Effect - Summary
❚ Greenhouse effect is essential to life on earth (we would freeze without it), but enhanced
greenhouse effect (caused in part by forest clearing and burning fossil fuels) may lead to
unwanted warming and serious consequences!
13
The Absorption Spectra of Plants
❚ Various substances (pigments) in plants have different absorption spectra:
❙ chlorophyll in plants absorbs red and violet light, reflects green and blue
❙ water absorbs strongly in red and IR, scatters violet and blue, leaving green at depth
Algae and Light Quality
❚ The quality of light is related to photosynthetic adaptations in the ocean:
❙ algae growing near the surface have pigments like those in terrestrial plants
(absorb blue and red, reflect green)
❙ algae growing at depth have specialized pigments that enable them to use green light more
effectively
Light Intensity
❚ Ecologists measure PAR (photosynthetically active radiation).
❚ Total radiation is measured as radiant flux = 1,400 W/m2 above the atmosphere (solar
constant).
❚ Radiant flux at earth’s surface is reduced by:
❙ nighttime periods
❙ low angle of incidence
❙ atmospheric absorption and scattering
❙ reflection from the surfaces of clouds
Topics 3: Temperature
The Thermal Environment
❚ Energy is gained and lost through various pathways:
❙ radiation - all objects emit electromagnetic radiation and receive this from
sunlight and from other objects in the environment
❙ conduction - direct transfer of kinetic energy of heat to/from objects in direct contact with
one another
convection - direct transfer of kinetic energy of heat to/from moving air and water
❙ evaporation - heat loss as water is evaporated from organism’s surface (2.43kJ/g at 30oC)
change in heat content = metabolism - evaporation + radiation+ conduction + convection
Organisms must cope with temperature extremes.
❚ Unlike birds and mammals, most organisms do not regulate their body temperatures.
❚ All organisms, regardless of ability to thermoregulate, are subject to thermal
constraints:
most life processes occur within the temperature range of liquid water, 0o-100oC
❙ few living things survive temperatures in excess of 45oC
❙ freezing is generally harmful to cells and tissues
Tolerance of Heat
❚ Most life processes are dependent on water in its liquid state (0-100oC).
❚ Typical upper limit for plants and animals is 45oC (some cyanobacteria survive to 75oC
and some archaebacteria survive to 110oC).
High temperatures:
❙ denature proteins
❙ accelerate chemical processes
❙ affect properties of lipids (including membranes)
14
Tolerance of Freezing
❚ Freezing disrupts life processes and ice crystals can damage delicate cell structures.
❚ Adaptations among organisms vary:
❙ maintain internal temperature well above freezing
❙ activate mechanisms that resist freezing
❘ glycerol or glycoproteins lower freezing point effectively (the “antifreeze”
solution)
❘ glycoproteins can also impede the development of ice crystals, permitting
“supercooling”
❙ activate mechanisms that tolerate freezing
❙ Organisms use physical stimuli to sense the environment.
❚ To function in complex and changing environments, organisms must:
❙ sense and detect environmental change (plants must sense changing seasons)
❙ detect and locate objects (predators must find food)
navigate the landscape (salmon must recognize their home river to spawn)
Sensing Electromagnetic Radiation
❚ Many organisms rely on vision (detection of visible light and other wavelengths):
❙ light has high energy
❙ light permits accurate location and resolution of targets
❚ Many variations in capabilities exist:
❙ hawks have extreme visual acuity
❙ insects and birds can perceive UV
❙ insects can detect rapid movements
❚ Animals operating in dark surroundings may sense IR (e.g., pit vipers utilize pit organs to
sense prey).
Sensing Sound
❚ Sounds are pressure waves created by movements, impacts, vibrations.
❚ Directional sensitivity possible by comparing signals received at two ears:
❙ sensitivity is greatest when the distance between ears matches wavelength (highpitched
sounds more useful to smaller animals)
❙ asymmetrical shapes of owls’ ears enable accurate pinpointing of source
❚ Other examples:
❙ bats echolocate using sound pulses they generate
❙ whales communicate over long distances using low-frequency sounds
Sensing Odors
❚ Smell is the detection of molecules diffusing through air or water.
❚ Odors differ from light and sound:
❙ odors are difficult to localize
❙ odors persist long after source has disappeared
❚ Moving “upstream” along a concentration gradient can help localize the source of
odor.
❚ Odors are the basis of much chemical communication:
❙ animals use odors to attract mates
❙ plants use odors to attract pollinators
15
Sensing Electrical Fields
❚ Some aquatic animals specialize in using and detecting electrical fields:
❙ some fish create electric fields and sense distortions caused by prey
❙ paddlefish sense distortions caused by prey
❙ other species use electrical signals to communicate
❙ electric ray uses powerful currents to defend itself and stun prey
Sensing Physical Contact
❚ Under conditions of poor visibility, catfish use fins and barbels as sensitive touch and taste
receptors.
❚ Physical contact is limited in its range, but useful under many circumstances.
❚ Touch can provide tremendous amount of information regarding texture and structure.
Summary 1
❚ Water is the basic medium for life. Its unique properties both constrain and provide
opportunities for living things.
❚ Biological energy transformations are based largely on the chemistry of carbon and oxygen,
with photosynthesis and respiration representing the most fundamental transformations of these
elements.
Summary 2
❚ Most of the energy for life comes from the sun in the form of electromagnetic radiation.
❚
Organisms have thermal budgets comprised of metabolism, radiation,
conduction,convection, and evaporation.
❚ Hot and cold environments pose special problems for organisms, requiring unique
adaptations.
❚ Organisms sense the physical environment via many stimuli.
Chapter Overview - Basics
❚ The physical world both provides the context for life and constrains its existence.
❚ A world of environmental factors...
❙ resources: water, minerals and food items
❙ conditions: temperature and relative humidity
❚ Most factors have extremely wide ranges:
❙ each type of organism is typically adapted to a narrow range of each factor
Chapter Overview - Regulation
❚ Organisms typically contrast with their external environments:
❙ internal conditions are maintained +/- constant
❙ fluxes of heat and substances must be regulated
❙ but organisms are open systems...
❘ resources must be acquired wastes must be eliminated
❚ How do organisms accomplish this?
Chapter Overview - Bottom Line
❚ It is important for us to understand the mechanisms organisms use to interact with their
environment.
❚ This understanding may lead to insights:
❙ why organisms are specialized
❙ why organisms have specific geographic distributions
why certain adaptations are associated with certain environments
16
What’s next?
❚ This chapter examines adaptations by considering various challenges
Facing organisms, for example:
❙ how do plants acquire water and nutrients from soils and transport these?
❙ how do plants carry out photosynthesis under varied environmental conditions?
how do plants and animals cope with extremes of temperature, water stress, and salinity?
Availability of Soil Water
❚ Water molecules are attracted to:
❙ each other (causes surface tension)
❙ surfaces (causes capillary action)
❚ When a soil is saturated and excess (gravitational) water drains:
❙ remaining water exists as thin films around soil particles (mineral and organic)
❙ the greater the area of such particles (as in clayey soils), the more water the soil
retains
All soil water molecules are not equal.
It’s all a matter of physical attraction...
❙ the closer a water molecule is to a soil particle, the greater the force with which it is
attracted
❙ this force is the matric potential of the soil, contributing to the overall water potential
❙ matric potentials (units are MPa or atm) are considered increasingly negative as they
represent greater attractive forces
It’s all a matter of potential...
❚ Soil water potential is:
❙ usually dominated by matric forces
❙ determined as the force required to remove the most loosely bound water
molecules
❚ Typical “benchmark” values are:
❙ -0.1 atm (field capacity)
❙ -15 atm (wilting point)
❙ -100 atm (exceedingly dry soil)
Plants obtain water from the soil.
❚ How do water molecules move?
❙ in the direction of more negative potential
❙ across most biological membranes
❚ Why does water move from the soil into plant roots?
❙ water potential in cells of the root hairs is more negative than that in the soil
❙ negative potential in root cells is generated mostly by solutes -- osmotic
potential
Membranes are selectively leaky.
❚ Can solutes exit root cells as readily as water enters?
❙ no, internal and external concentrations would equilibrate and osmotic potential gradient
would disappear
❙ cell membranes are semipermeable; large molecular weight solutes
(carbohydrates and proteins) cannot readily leave the cell
So why does water move into roots?❚
17
Internal (cellular) osmotic potential is more negative than external (soil) matric potential, up to a
point:
root hair cells with 0.7 molar concentration of solutes maintain inward flux of water
against a soil matric potential as low as -15 atm:
as soil becomes drier, water flux ceases and may reverse, leading to wilting and death
desert plants may obtain water to soil matric potentials as low as -60 atm (high solute conc.)
Moving Water from Roots to Leaves
Once water is in root cells, then what?
water moving to the top of any plant must overcome tremendous forces caused by gravity and
friction in conducting elements (xylem):
opposing force is generated by evaporation of water from leaf cells to atmosphere
(transpiration)
❘ water potential of air is typically highly negative (potential of dry air at 20 oC is -1,332 atm)
❘ force generated in leaves is transmitted to roots -- water is drawn to the top of the plant
(tension-cohesion theory)
Adaptations to Arid Environments 1
❚ Most water exits the plant as water vapor through leaf openings called stomates:
❙ plants of arid regions must conserve limited water while still acquiring CO2 from the
atmosphere (also via stomates) - a dilemma!
potential gradient for CO2 entering plant is substantially less than that for water exiting the plant
heat increases the differential between internal and external water potentials, making matters
worse
Adaptations to Arid Environments 2
❚ Numerous structural adaptations address challenges facing plants of arid regions by:
❙ reducing heat loading:
❘ increase surface area for convective heat dissipation
❘ increase reflectivity and boundary layer effect with dense hairs and spines
❙ reducing evaporative losses:
❘ protect surfaces with thick, waxy cuticle
❘ recess stomates in pits, sometimes also hair-filled
Plants obtain mineral nutrients from soil water.
❚ Nutrients must move from the soil solution into cells of root hairs…
❙ a nutrient element moves passively (via diffusion) into root when its
concentration in soil water exceeds that of root cells
❙ when nutrient concentration in soil water is lower than that in roots, active uptake
(energy-demanding) is essential
Other Plant Strategies for Obtaining Nutrients
❚ Enlist partners!
❙ many plants have intimate associations (symbioses) with fungi -- fungal partners enhance
mineral absorption
❚ Regulate growth!
❙ plants of nutrient-poor soils typically:
❘ grow slowly, maintain leaves for multiple growing seasons (evergreenness), and store
surplus
❘ shift growth toward more root and less shoot
18
Plant Mineral Nutrition - a Case Study in Patchiness
Distributions of nutrients in soils is highly patchy (heterogeneous) - how does such patchiness
affect plant mineral nutrition?
❙ ragweed and pokeweed plants, when grown in monoculture, performed best when soil
nutrients were patchy instead of homogeneous
when these plants were grown together, advantage of patchy nutrients
disappeared
Photosynthesis varies with levels of light.
❚ Photosynthetic rate is a function of light intensity (proportional to light intensity at low light
levels, leveling off at high levels):
❙ in dim light, plants fail to offset respiratory losses with photosynthetic gains
❙ as light intensity increases, a break-even point (losses offset by gains) is reached, called
compensation point
❙ at saturation point, further increase in light level does not stimulate further photosynthesis
Plants modify photosynthesis in stressful environments.
❚ Fixation of atmospheric carbon into glucose (dark reactions of photosynthesis) is
accomplished by Calvin cycle:
❙ first step involves synthesis of two 3-carbon molecules (PGA) from RuBP and CO2: CO2 +
❙ enzyme accomplishing this is RuBP carboxylase...
C3 Photosynthesis
❚ C3 plants depend solely on Calvin Cycle for photosynthetic CO2 fixation.
❚ C3 plants have certain disadvantages:
❙ RuBP carboxylase has low affinity for its substrate, CO2
❙ RuBP carboxylase also catalyzes the oxidation of PGA when leaf [CO2] low and [O2] high,
especially at high temperatures
C4 Photosynthesis❚
is fixed to OAA in mesophyll cells, then shuttled to bundle
sheath cells where CO2 is unloaded for use in Calvin cycle
❙ PEP regenerated in bundle sheath cells is reused (shuttled back to mesophyll)
Advantages of C4 Photosynthesis
❙ Biochemical and anatomical features lead to photosynthetic advantages:
❘ Calvin cycle isolated from high O2 levels while supplied with high levels of CO2 leads to much more efficient operation
❘ PEP carboxylase has high affinity for CO2, thus permitting plant to obtain CO2
while increasing stomatal resistance to water loss
❘ these advantages come at an energy cost, but are especially helpful under
conditions of high light, high temperature and water stress
Photosynthesis in Hot/Arid Environments
❚ C4 photosynthesis favored as environmental conditions become increasingly hot/arid:
❙ latitudinal gradients quite conspicuous: C4 plants become much more common in
transect from polar regions toward equatorial regions
❙ but, C3 species are favored in cooler, moister habitats because:
❘ disadvantages of C3 photosynthesis are lessened
❘ C3 approach is biochemically more energy-efficient
19
Carbon Assimilation in CAM Plants
❚ Some plants (succulents in several families) add a temporal “twist” to C4 process...
❙ CO2 is acquired at night when evaporative demand is lowest
❙ carbon from CO2 is stored in 4-C organic acids (such as OAA)
❙ stored carbon is used by Calvin cycle during daylight hours when energy is available for
dark reactions
Balancing Salt and Water
❚ Osmotic regulation is not just a problem for plants
❚ Aquatic animals are rarely in equilibrium with their surroundings:
❙ fresh-water fish are hyperosmotic (internal salt concentration higher than that of medium)
❙ marine fish are hypo-osmotic (internal salt concentration lower than that of medium)
Ion retention is critical to freshwater organisms.
❚ Freshwater fish must eliminate excess water and selectively retain dissolved ions:
❙ they gain water by osmosis
❙ they eliminate excess water in their urine
❙ their kidneys selectively retain dissolved ions
❙ active uptake of ions via gills is also important
Water retention is critical to marine organisms.
❚ Saltwater fish must retain water and excrete excess ions:
❙ they tend to lose water to surrounding sea water and must drink to replace this
❙ excess salt must be excreted from gills and kidneys
❙❙ some fish (sharks and rays) raise osmotic potential of blood by retaining waste nitrogen as
urea -- their high internal osmotic potential matches that of seawater
Water and Salt Balance in Terrestrial Plants
❚ Plants take up excessive salts along with water, especially in saline soils.
plants must actively pump salts back into soil
❚ In coastal mudflats, mangroves must acquire water while excluding salts. They:
❙ establish high root osmotic concentrations to maintain water movement into root
❙ exclude salts at the roots and also excrete excessive salts from specialized leaf glands
Water and Salt Balance in Terrestrial Animals
❚ Terrestrial animals must eliminate excess salts acquired in diet:
❙ copious amounts of water can serve to flush excess salts in more humid climates where
water is scarce, other options exist:
❘ desert mammals produce highly concentrated urine；birds and reptiles eliminate excess salts
via salt glands； Animals excrete excess nitrogen.
Carnivorous animals acquire excess nitrogen from their high-protein diet:
❙ excess nitrogen must be eliminated:
❘ aquatic animals eliminate nitrogen as ammonia
❘ terrestrial animals cannot afford copious amounts of water necessary for elimination of
ammonia
• mammals excrete urea
• birds and reptiles excrete uric acid, which can be eliminated with very little water
20
Conserving Water in Hot Environments 1
❚ Animals of deserts may experience environmental temperatures in excess of body
temperature:
❙ evaporative cooling is an option, but water is scarce
❙ animals may also avoid high temperatures by:
❘ reducing activity
❘ seeking cool microclimates
❘ migrating seasonally to cooler climates
Conserving Water in Hot Environments 2
❚ Desert plants reduce heat loading in several ways already discussed. Plants may, in addition:
❙ orient leaves to minimize solar gain
❙ shed leaves and become inactive during stressful periods
The Kangaroo Rat - a Desert Specialist
❚ These small desert rodents perform well in a nearly waterless and extremely hot setting.
❙ kangaroo rats conserve water by:
❘ producing concentrated urine
❘ producing nearly dry feces
❘ minimizing evaporative losses from lungs
❙ kangaroo rats avoid desert heat by:
❘ venturing above ground only at night
❘ remaining in cool, humid burrow by day
Organisms maintain a constant internal environment.❙
An organism’s ability to maintain constant internal conditions in the face of a varying
environment is called homeostasis:
❙ homeostatic systems consist of sensors, effectors, and a condition maintained constant
all homeostatic systems employ negative feedback -- when the system deviates from set
point, various responses are activated to return system to set point
Temperature Regulation: an Example of Homeostasis
❚ Principal classes of regulation:
❙ homeotherms (warm-blooded animals) - maintain relatively constant internal temperatures
❙ poikilotherms (cold-blooded animals) - tend to conform to external temperatures
❘ some poikilotherms can regulate internal temperatures behaviorally, and are thus considered
ectotherms, while homeotherms are endotherms
Homeostasis is costly.
❚ As the difference between internal and external conditions increases, the cost of maintaining
constant internal conditions increases dramatically:
❙ in homeotherms, the metabolic rate required to maintain temperature is directly
proportional to the difference between ambient and internal temperatures
Limits to Homeothermy
❚ Homeotherms are limited in the extent to which they can maintain conditions different
from those in their surroundings:
❙ beyond some level of difference between ambient and internal, organism’s capacity to return
internal conditions to norm is exceeded
❙ available energy may also be limiting, because regulation requires substantial energy output
Partial Homeostasis
21
❚ Some animals (and plants!) may only be homeothermic at certain times or in certain
tissues…
❘ pythons maintain high temperatures when incubating eggs
❘ large fish may warm muscles or brain
❘ some moths and bees undergo pre-flight warm-up
❘ hummingbirds may reduce body temperature at night (torpor)
Delivering Oxygen to Tissues
❚ Oxidative metabolism releases energy.
❚ Low O2 may thus limit metabolic activity:
❙ animals have arrived at various means of delivering O2 to tissues:
❘ tiny aquatic organisms (<2 mm) may rely on diffusive transport of O2
❘ insects use tracheae to deliver O2
❘ other animals have blood circulatory systems that employ proteins (e.g.,hemoglobin) to bind
oxygen
Countercurrent Circulation
❚ Opposing fluxes of fluids can lead to efficient transfer of heat and substances:
❙ countercurrent circulation offsets tendency for equilibration (and stagnation)
❙ some examples:
❘ in gills of fish, fluxes of blood and water are opposed, ensuring large O2 gradient and thus
rapid flux of O2 into blood across entire gill structure
❘ similar arrangement of air and blood flow in the lungs of birds supports high rate of O2
delivery
Conservation and Countercurrents
❚ Countercurrent fluxes can also assist in conservation of heat; here are two examples:
birds of cold regions conserve heat through countercurrent circulation of blood in legs
❘ warm arterial blood moves toward feet cooler venous blood returns to body core
❘ heat from arterial blood transferred to venous blood returns to core instead of being lost to
environment
❙ kangaroo rats use countercurrent process to reduce loss of moisture in exhaled air
Each organism functions best under a restricted range of conditions.
❚ Organisms function best in a relatively narrow range of conditions, the optimum:
❙ optimum is a result of natural selection for biochemical properties of enzymes and lipids, as
well as internal structures, body form, etc.
❙ such specialization precludes efficient function across wide ranges of conditions, which
would be expensive and compromise optimal function
Compensation is possible.
❚ Many organisms accommodate to predictable environmental changes through their
ability to “tailor” various attributes to prevailing conditions:
❙ rainbow trout are capable of producing two forms of the enzyme, acetylcholine esterase:
❘ winter form has highest substrate affinity between 0 and 10oC
❘ summer form has highest substrate affinity between 15 and 20oC
Adaptation is the key to under-standing success of organisms. Organisms living in different
environments function equally well under their constraints:
22
❙ Antarctic and tropical fish both swim actively!
Acclimatization permits some degree of adjustment to changing conditions: ❙
rainbow trout example
❙ rapid adjustment of O2 transport capabilities to changing partial pressure of O2 with
elevation in vertebrates, including humans
Summary
❚ The mechanisms by which organisms interact with their physical environment help us
understand why organisms are specialized to narrow ranges of conditions and how adaptations
of morphology and physiology are associated with certain conditions.
Topics 4: Climate
Background
Variations in the physical environment underlie the diversity of biological systems.
determinants of this
variation.
Climate is perhaps the most important element of environmental variation.
Background, Cont’d
Conditions of temperature, light, substrate, moisture, and other factors shape:
distributions of organisms
adaptations of organism
Earth has many distinctive climatic zones:
within these zones, topography and soils further differentiate the environment
Focus on Climate - Spatial Variation
edictable:
large-scale (global) patterns primarily related to latitudinal distribution of solar energy
regional patterns primarily related to shapes and positions of ocean basins, continents, and
mountain ranges
- extent and location of stochastic perturbations
Focus on Climate - Temporal Variation
variation:
predictable:
seasonal variation
unpredictable:
-scale events (El Niño, cyclonic storms)
all-scale events (variable weather patterns)
Earth as a Solar-powered Machine
❚ Earth’s surface and adjacent atmosphere are a giant heat-transforming machine:❘
solar energy is absorbed differentially over planet
❙ this energy is redistributed by winds and ocean currents, and is ultimately returned to space
❙ there are interrelated consequences:
latitudinal variation in temperature and precipitation
❘ general patterns of circulation of winds and oceans
23
Global Patterns in Temperature and Precipitation
From the equator poleward, we encounter dual global trends of:
Why? At higher latitudes:
Temporal Variation in Climate with Latitude
❚ Temporal patterns are predictable (diurnal, lunar, and seasonal cycles).
❚ Earth’s rotational axis is tilted 23.5o relative to its path around the sun, leading to:
❙ seasonal variation in latitude of most intense solar heating of earth’s surface
❙ general increase in seasonal variation from equator poleward, especially in N hemisphere
Hadley Cells
❚ Hadley cells constitute the principal patterns of atmospheric circulation:
❙ warm, moist air rising in the tropics spreads to the north and south
❙ as this air cools, it eventually sinks at about 30o N or S latitude, then returns to tropics at
surface
❙ this pattern drives secondary temperate cells (30-60o N and S of equator), which, in turn,
drive polar cells (60-90o N and S of equator)
The Intertropical Convergence
❚ Surface currents of air in tropical Hadley cells converge near the equator.
❚ Warm, moist air rising in equatorial regions cools and loses much of its moisture
content as precipitation there.
❚ As cool, dry air descends and warms near 30o N and S latitude, its capacity to
hold moisture increases, resulting in prevalence of arid climates at these latitudes.
Surface Winds
❚ Surface flow of air in Hadley cells is deflected by earth’s rotation
❙ to the right in N hemisphere
❙ to the left in S hemisphere
❚ Net effect of deflections on surface flows:
❙ air flows toward the west in tropical cells
❙ air flows toward the east in temperate cells
❙ air flows again toward the west in polar cells
Rain Shadows
❚ Moisture content of air masses is recharged when they flow over bodies of water:
❙ rain falls more plentifully in S hemisphere (81% of surface there is water,
versus 61% in N hemisphere)
❚ Air masses forced over mountains cool and lose moisture as precipitation.
❚ Air on lee side of mountains is warmer and drier (causing rain shadow effect).
Proximity to bodies of water determines regional climate.
Areas downwind of large mountain ranges are typically more arid (rain shadow effect).
❚ Continental interiors are also typically arid:
❙ distant from source of moisture recharge
❙ air masses reaching these areas are likely to have previously lost moisture
24
❚ Coastal areas have less variable maritime climates than continental interiors.
Ocean currents redistribute heat and moisture.
❚ Ocean surface currents propelled by winds.
❚ Deeper currents established by gradients of temperature and salinity.
❚ Ocean currents constrained by basin configuration, resulting in:
❙ clockwise circulation in N hemisphere
❙ counterclockwise circulation in S hemisphere
❚ Warm tropical waters carry heat poleward.
Western coasts have Cold currents.
❚ Oceanic water circulation:
❙ cold polar water forced equatorward from the poles along west coasts of major continents
❙ this water acts as a barrier to warm, moist air
❙ net result is coastal deserts, especially on west coasts of South America and Africa
❚ Equatorward flows are deflected to W in both hemispheres, causing upwelling of cold,
nutrient-laden water in these regions.
Seasonal Variation in Climate
❚ Seasonal progression of sun’s zenith causes familiar patterns of temperature.
❚ Intertropical convergence also migrates seasonally:
❙ region of high precipitation shifts N or S with intertropical convergence
❙ regions of arid conditions (30o N and S of intertropical convergence) shift
accordingly
Seasonality of Rainfall in Tropics
❚ Latitudes between about 20oS and 20oN experience greatest seasonality of precipitation.
❚ Some examples:
❙ Mérida (20oN) - has a single summer rainy season, alternating with a long dry season
❙ Rio de Janiero (20oS) - pattern similar to that of Mérida, but displaced 6 months
❙ Bogotá (0o) - two rainy seasons, spring/fall, separated by drier periods
Similar Patterns Outside Tropics
❚ At 30oN in Chihuahuan Desert:
❙ at northward limit of intertropical convergence, summer rainfall, winter drought
❚ At 35oN in San Diego:
❙ beyond northward limit of intertropical convergence, summer drought, winter rainfall
(Mediterranean-type climate)
Seasonal Cycles in Temperate Lakes 1
The four seasons of a small temperate lake - each season has its own
characteristic temperature profile:
25
❙ winter: coldest water (0oC) at surface, just beneath ice layer, increasing to 4oC near bottom
❙ spring: ice melts; as surface warms, denser water sinks, resulting in uniform 4oC profile,
with little resistance to wind-driven spring overturn
Seasonal Cycles in Temperate Lakes 2
❙ summer: continued warming of surface results in thermal stratification, a stable situation and
resistant to overturn; strata established:
❘ epilimnion - warm, less dense surface water
❘ thermocline - zone of rapid temperature change
❘ hypolimnion - cool, denser bottom water (may become oxygen-depleted)
❙ fall: water cooling at surface sinks, destroying stratification, once again
permitting wind-driven fall overturn
Topographic and Geologic Features
❚ Topography can modify environment on local scale:
❙ steep slopes typically drain well, leading to xeric conditions
❙ bottomlands moist and may support riparian forests, even in arid lands
❙ in N hemisphere, south-facing slopes are warmer and drier than north-facing slopes
Gradients in Mountains
❚ Adiabatic cooling of air masses crossing mountain barriers leads to:
❙ temperature decrease of 6o-10oC for each 1,000 m increase in elevation
❙ precipitation typically increases
❚ Some consequences:
in tropics, snow line is reached at 5,000 m
❙ in temperate zone, +1,000 m of altitude corresponds to +800 km of latitude
More on Mountain Climates
❚ Decrease in temperature as air masses are forced over mountains is the result of
adiabatic cooling (air expands, performs work, and therefore cools).
❚ As air cools, its capacity to hold moisture declines, forcing moisture out as rain/snow.
❚ Descending air rewarms, resulting in warm and dry air at base of lee side of mountain.
Life Zones in Southwestern Mountains
Nineteenth-century naturalist, C.H. Merriam, recognized life zones, prominent in the American
Southwest:
in Lower Sonoran Zone, subtropical plants and animals (hummingbirds, ringtailed cats, etc.)
make their only Temperate Zone appearances
❙ In Alpine Zone, 2,600 m higher, landscape resembles tundra of northern
Canada, 2,000 km to the north
Climate and Soil
❚ Climate exerts indirect effect on distributions of plants and animals through its influence on
development of soils.
❚ What are soils?
❙ chemically and biologically altered materials overlying unaltered parent
materials at earth’s surface
❙ soil contains unaltered and modified minerals, organic matter, air, water, living organisms
Soil Characteristics
26
❚ Soils are the product of climate, parent material, vegetation and other organisms, local
topography, and time.
❚ Soils often have distinct layers or horizons:
❙ O (dead organic matter)
❙ A1 (humus rich) and A2 (zone of leaching)
❙ B (low organic matter, deposition of clays)
❙ C (weakly altered material resembling parent material)
Soils exist in a dynamic state.
❚ Soils change through time:
❙ water leaches materials
❙ vegetation adds organic material
❙ other materials enter through precipitation, dust, and from underlying rock
❚ Rate of development varies:
❙ in arid regions, soils may be shallow
❙ in humid tropics, soils may develop to 100 m
Weathering
❚ Weathering = physical and chemical alteration of rock or other parent material near earth’s
surface.
❚ Various processes characterize weathering:
❙ freeze/thaw cycles break rock and expose it to chemical action
❙ water dissolves readily soluble materials
❙ other processes lead to synthesis of new minerals, such as clays❙
Synthesis of Clay Minerals
❚ Common minerals, such as feldspar and mica, can be chemically altered to form clay
minerals:
❙ these minerals are K, Mg, Fe aluminosilicates H+ ions displace K and Mg Fe, Al, and Si
form new insoluble clay minerals clay minerals are important to water-holding and
cation-exchange properties of soils H+ ions are essential for clay synthesis.
❚ What is the source of this acidity?
rainwater is naturally acidic; carbonic acid is formed when CO2 dissolved in rainwater; results
in natural pH of about 5.
❙ additional acidity is produced by oxidation of biological materials, producing CO2 and more
carbonic acid. acidity formed by oxidation of biological materials is more significant in the
tropics
Podzolization
❚ Podzolization occurs when clay particles break down in the A horizon and their soluble ions
are transported downward.
❚ This process is most likely to occur in cold regions where needle-leaved trees predominate:
❙ organic acids percolate through soil under humid climate regime, leaving leached A2, with
deposition in B horizon below
Laterization
❚ In warm, wet conditions of tropics and subtropics, soils weather to great depths:
❙ clay particles break down
❙ silica is leached from soil
❙ residue is rich in oxides of iron and aluminum
27
Consequences of Laterization
❚ Lateritic soils
❙ are usually not acidic
❙ are infertile; they contain little clay or humus to hold cations, which are easily leached
❙ are deeply weathered, so minerals released from weathering of parent material are not
accessible to plants
❚ Rich soils do develop in tropics, in mountainous areas and on volcanic deposits.
Soils -- Bottom Line
❚ Soil formation emphasizes the role of the physical environment, particularly climate,
geology, and landforms, in creating the tremendous variety of environments for life that exist at
the surface of the earth and in its waters.
Summary 1
❚ Global environmental patterns are the result of differential input of solar irradiation in
different regions and redistribution of heat energy by winds and ocean currents.
❚ Seasonality in terrestrial environments is caused by the latitudinal movement of the solar
equator. Seasonal changes in energy budgets profoundly affect temperate lakes.
Summary 2
❚ Irregular and unpredictable variations in climate, such as severe El Niño-Southern
Oscillation events, may disrupt biological communities on a global scale.
❚ Topography and geology superimpose local environmental variation on more general
climatic patterns.
❚ Soil properties contribute to local variation in terrestrial environments.
作业布置
课后小结
28
课
题
Lecture 3: Population Growth and Regulation
学
时
4
教学目标
与要求
3.1 Population grow by multiplication rather than addition
3.2 Age structure influences population rate
3.3 A life table summaries age-specific schedules of survival and fecundity
3.4 The intrinsic rate of increase can be estimated from the life table
3.5 Population size is regulated by density-dependent factors
掌握 water 对生物的影响规律
重
点
light and climate 对生物的影响规律
难
点
讲授、讨论、多媒体
教学方法
与手段
1、The economy of nature，6 th ed，Robert E. Ricklefs，2008 by W. H. Freeman and
Company；
2. General
Ecology, 2th ed., David T. Krohne. Thomson Learning, Inc.
ISBN
0-534-37528-6;
3. Ecology : Concepts and Applications 4th ed McGraw-Hill Companies, Inc. ;
参考资料
4. Ecology :From Individuals to Ecosystems,4th ed published 2006, Blackwell
Publishing;；
5.孙儒泳，李庆芬，牛翠娟，娄安如. 2002. 基础生态学. 高等教育出版社；
6.孙儒泳，李博，诸葛阳，尚玉昌编. 1992. 普通生态学. 高等教育出版社；
7. 李博主编. 1999. 生态学. 高等教育出版社；
8. 盛连喜主编，2005，
《环境生态学导论》，高等教育出版社。
29
教学内容及过程
Human Population Growth 1
❚ Growth of the human population is one of the most significant ecological
developments in the earth’s history.
❚ Early population growth was very slow:
❙ 1 million individuals lived a million years ago
❙ 3-5 million individuals lived at the start of the agricultural revolution (10,000 years ago)
Human Population Growth 2
❚ More recent population changes have been quite rapid:
❙ population increased 100-fold from 10,000 years ago to start of eighteenth century
❙ in the past 300 years, population has increased from 300 million to 6 billion, a 20-fold increase
❙ the most recent doubling (3 billion to 6 billion) has taken place in the last 40 years
How many humans?
❚ Has the human population exceeded the ability of the earth to support it?
❙ there is no consensus on this point
❙ clearly, continued growth will further stress the biosphere
❚ When, and at what level, will the human population cease to grow?
❙ there are many unknowns
❙ the United Nations estimates a plateau at 9 billion
Demography
❚ Demography is the study of populations:
❙ involves the use of mathematical techniques to predict growth of populations
❙ involves intensive study of both laboratory and natural populations, with
emphasis on:
❘ causes of population fluctuations
❘ effects of crowding on birth and death rates
Populations grow by multiplication.
❚ A population increases in proportion to its size, in a manner analogous to a savings account
earning interest on principal:
❙ at a 10% annual rate of increase:
❘ a population of 100 adds 10 individuals in 1 year
❘ a population of 1000 adds 100 individuals in 1 year
❙ allowed to grow unchecked, a population growing at a constant rate would rapidly climb
toward infinity
Two Models of Population Growth
❚ Because of differences in life histories among different kinds of organisms, there is a need for
two different models (mathematical expressions) for population growth:
❙ exponential growth: appropriate when young individuals are added to the population
continuously
❙ geometric growth: appropriate when young individuals are added to the population at one
particular time of the year or some other discrete interval
30
Exponential Population Growth 1
❚ A population exhibiting exponential growth has a smooth curve of population increase as a
function of time.
❚ The equation describing such growth is: N(t) = N(0)ert
where:N(t) = number of individuals after t time units
N(0) = initial population size
r = exponential growth rate
e = base of the natural logarithms (about 2.72)
Exponential Population Growth 2
❚ Exponential growth results in a continuously accelerating curve of increase (or continuously
decelerating curve of decrease).
❚ The rate at which individuals are added to the population is: dN/dt = rN
❚ This equation encompasses two principles:
❙ the exponential growth rate (r) expresses population increase on a “per individual basis”
❙ the rate of increase (dN/dt) varies in direct proportion to N❚
Geometric Population Growth 1
Geometric growth results in seasonal patterns of population increase and decrease.
The equation describing such growth is: N(t + 1) = N(t)
where:N(t + 1) = number of individuals after 1 time unit
N(t) = initial population size
= ratio of population at any time to that 1 time
unit earlier, such that ë = N(t + 1)/N(t)
Geometric Population Growth 2
❚ To calculate the growth of a population over many time intervals, we multiply the original
population size by the geometric growth rate for the appropriate number of intervals t:
N(t) = N(0)  t
❚ For a population growing at a geometric rate of 50% per year ( = 1.50), an initial population
of N(0) = 100 would grow to N(10) = N(0)  10 = 5,767 in 10 years.
Exponential and geometric growth are related.
❚ Exponential and geometric growth equations describe the same data equally well.
❚ These models are related by:
 = er
and loge = r
Varied Patterns of Population Change
❚ A population is:
❙ growing when > 1 or r > 0
❙ constant when = 1 or r = 0
❙ declining when< 1 (but > 0) or r < 0
Per Individual Population Growth Rates
❚ The per individual or per capita growth rates of a population are functions of component birth
(b or B) and death (d or D) rates: r = b – d and  = B - D
❚ While these per individual or per capita rates are not meaningful on an individual basis, they
take on meaning at the population level.
31
Age structure determines population growth rate.
❚ When birth and death rates vary with the age of individuals in the population, contributions of
younger and older individuals must be calculated separately.
❚ Age specific schedules of survival and fecundity enable us to project the population’s size and
age structure into the future.
Stable Age Distribution
❚ When a population grows with constant schedules of survival and fecundity, the population
eventually reaches a stable age distribution (each age class represents a constant percentage of the
total population):
❚ Under a stable age distribution:
❙ all age classes grow or decline at the same rate, λ
❙ the population also grows or declines at this constant rate, λ
Life Tables
❚ Life tables summarize demographic information (typically for females) in a convenient format,
including: age (x) number alive
❙ survivorship (lx): lx = s0s1s2s3 ... sx-1
❙ mortality rate (mx)
❙ probability of survival between x and x+1 (sx)
❙ fecundity (bx)
Cohort and Static Life Tables
❚ Cohort life tables are based on data collected from a group of individuals born at the same
time and followed throughout their lives:
❙ difficult to apply to mobile and/or long-lived animals
❙ used by Grants to construct life tables for Darwin’s finches on Galápagos
Islands
❚ Static life tables consider survival of individuals of known age during a single time interval:
❙ require some means of determining ages of individuals
❙ used by Olaus Murie to construct life tables for Dall mountain sheep in Denali National Park
The Intrinsic Rate of Increase 1
❚ The Malthusian parameter (rm) or intrinsic rate of increase is the exponential rate of increase
(r) assumed by a population with a stable age distribution.
❚ rm is approximated (ra) by performing several computations on a life table, starting with
computation of R0, the net reproductive rate, (Σlxbx) across all age classes.
The Intrinsic Rate of Increase 2
❚ The net reproductive rate, R0, is the expected total number of offspring of an individual over
the course of her life span.
❙ R0 = 1 represents the replacement rate
❙ R0 < 1 represents a declining population
❙ R0 > 1 represents an increasing population
❚ The generation time for the population is calculated as T = Σxlxbx/Σlxbx
The Intrinsic Rate of Increase 3
❚ Computation of ra is based on R0 and T as follows: ra = logeR0/T
❚ Clearly, the intrinsic rate of natural increase depends on both the net
reproductive rate and the generation time:
32
❙ large values of R0 and small values of T lead to the most rapid population growth
Most populations have a great biological growth potential.
❚ Consider the population growth of the ring-necked pheasant:
❙ 8 individuals introduced to Protection Island, Washington, in 1937, increased to 1,325 adults in
5 years: 166-fold increase
❘ r = 1.02, λ = 2.78
❙ another way to quantify population growth is through doubling time:
❘ t2 = loge2/loge λ = 0.69/loge λ = 0.675 yr or 246 days for the ring-necked pheasant
Environmental conditions and intrinsic rates of increase.
❚ The intrinsic rate of increase depends on how individuals perform in that population’s
environment.
❚ Individuals from the same population subjected to different conditions can establish the
reaction norm for intrinsic rate of increase across a range of conditions:
❙ these vary within and between species Intrinsic rate of increase is balanced by extrinsic
factors.
❚ Despite potential for exponential increase, most populations remain at relatively stable levels why?
❙ this paradox was noted by both Malthus and Darwin
❙ for population growth to be checked requires a decrease in the birth rate, an increase in the
death rate, or both
Consequences of Crowding for Population Growth
❚ Crowding:
❙ results in less food for individuals and their offspring
❙ aggravates social strife
❙ promotes the spread of disease
❙ attracts the attention of predators
❚ These factors act to slow and eventually halt population growth.
The Logistic Equation
❚ In 1910, Raymond Pearl and L.J. Reed analyzed data on the population of the United States
since 1790, and attempted to project the population’s future growth.
❚ Census data showing a decline in the exponential rate of population growth suggested that r
should decrease as a function of increasing N.
Behavior of the Logistic Equation
❚ The logistic equation describes a population that stabilizes at its carrying capacity, K:
❙ populations below K grow
❙ populations above K decrease
❙ a population at K remains constant
❚ A small population growing according to the logistic equation exhibits sigmoid growth.
❚ An inflection point at K/2 separates the accelerating and decelerating phases of population
growth.
The Proposal of Pearl and Reed
❚ Pearl and Reed proposed that the relationship of r to N should take the form: r = r0(1 - N/K)
in which K is the carrying capacity of the environment for the population.
33
❚ The modified differential equation for population growth is then the logistic equation:
dN/dt = r0N(1 - N/K)
Pearl and Reed’s Projections
❚ Pearl and Reed projected a U.S. population stabilized at 197,273,000.
❚ The U.S. population reached this level between 1960 and 1970 and has continued to grow
vigorously.
❚ Pearl and Reed could not have foreseen improvements in public health and medical treatment
that raised survival rates.
Population size is regulated by density-dependent factors.
❚ Only density-dependent factors, whose effects vary with crowding, can bring a population
under control; such factors include:
❙ food supply and places to live
❙ effects of predators, parasites, and diseases
❚ Density-independent factors may influence population size but cannot limit it; such factors
include:
❙ temperature, precipitation, catastrophic events
Density Dependence in Animals
❚ Evidence for density-dependent regulation of populations comes from laboratory experiments
on animals such as fruit flies:
❙ fecundity and life span decline with increasing density in laboratory
populations
❚ Populations in nature show variation caused by density-independent factors, but also show the
potential for regulation by density-dependent factors:
❙ song sparrows exhibit density dependence of territory acquisition, fledging of young, and
juvenile survival on density
Density Dependence in Plants 1
❚ Plants experience increased mortality and reduced fecundity at high densities, like animals.
❚ Plants can also respond to crowding with slowed growth:
❙ as planting density of flax seeds is increased, the average size achieved by individual plants
declines and the distribution of sizes is altered
Density Dependence in Plants 2
❚ When plants are grown at very high densities, mortality results in declining density:
❙ growth rates of survivors exceed the rate of decline of the population, so total weight of the
planting increases:
❘ in horseweed, a thousand-fold increase in average plant weight offsets a hundred-fold decrease
in density
Self-Thinning Curve
❚ A graph of log (average weight) versus log (density) for plants undergoing density-induced
mortality has points falling on a line with slope of approximately -3/2:
❙ this kind of graphical representation is known as a self-thinning curve
❙ similar patterns are seen for a wide variety of plants:
❘ this relationship is known as the -3/2 power law
34
Summary 1
❚ Population growth can be described by both exponential and geometric growth equations.
❚ When birth and death rates vary by age, predicting future population growth requires
knowledge of age-specific survival and fecundity.
❚ Life tables summarize demographic data.
❚ Analyses of life table data permit determination of population growth rates and stable age
distributions.
Summary 2
❚ Populations have potential for explosive growth, but all are eventually regulated by scarcity of
resources and other density-dependent factors. Such factors restrict growth by decreasing birth and
survival rates.
❚ Density-dependent population growth is described by the logistic equation.
❚ Both laboratory and field studies have shown how population regulation may be brought about
by density-dependent processes.
作业布置
课后小结
35
课
题
Lecture 4: Species Interaction
学
时
2
教学目标
与要求
4.1 All organisms are involved in consumer-resource interactions
4.2 Dynamics of consumer-resource interactions reflect mutual evolutionary responses
4.3 Parasites maintain a delicate consumer-resource relationship with their hosts
4.4 Herbivory varies the the quality of plants as resources
4.5 Competition may be an indirect results of other types of interactions
4.6 Individuals of different species can collaborate in mutualistic interactions
4.1 All organisms are involved in consumer-resource interactions
4.2 Dynamics of consumer-resource interactions reflect mutual evolutionary responses
重
点
Competition may be an indirect results of other types of interactions
难
点
讲授、讨论、多媒体
教学方法
与手段
1、The economy of nature，6 th ed，Robert E. Ricklefs，2008 by W. H. Freeman and
Company；
2. General
Ecology, 2th ed., David T. Krohne. Thomson Learning, Inc.
ISBN
0-534-37528-6;
3. Ecology : Concepts and Applications 4th ed McGraw-Hill Companies, Inc. ;
参考资料
4. Ecology :From Individuals to Ecosystems,4th ed published 2006, Blackwell
Publishing;；
5.孙儒泳，李庆芬，牛翠娟，娄安如. 2002. 基础生态学. 高等教育出版社；
6.孙儒泳，李博，诸葛阳，尚玉昌编. 1992. 普通生态学. 高等教育出版社；
7. 李博主编. 1999. 生态学. 高等教育出版社；
8. 盛连喜主编，2005，
《环境生态学导论》，高等教育出版社。
36
教学内容及过程
Consumer-Resource Interactions
❚ All life forms are both consumers and victims of consumers.
❚ Consumer-resource interactions organize biological communities into consumer chains (food
chains):
❙ consumers benefit at the expense of their resources
❙ populations are controlled from below by resources and from above by consumers
Some Definitions
❚ Predators catch individuals and consume them, removing them from the prey population.
❚ Parasites consume parts of a living prey organism, or host:
❙ parasites may be external or internal
❙ a parasite may negatively affect the host but does not directly remove it from the population
More Definitions
❚ Parasitoids consume the living tissues of their hosts, eventually killing them:
❙ parasitoids combine traits of parasites and predators
❚ Herbivores eat whole plants or parts of plants:
❙ may act as predators (eating whole plants) or as parasites (eating parts of plants):
❘ grazers eat grasses and herbaceous vegetation
❘ browsers eat woody vegetation
Detritivores occupy a special niche.
❚ Detritivores consume dead organic material, the wastes of other species:
❙ have no direct affect on populations that produce these resources:
❘ do not affect the abundance of their food supplies
❘ do not influence the evolution of their resources
❙ are important in the recycling of nutrients within ecosystems
Predators have adaptations for exploiting their prey.
❚ Predators vary in size relative to their prey:
❙ predators may be much larger than their prey (whales are far larger than krill and small fish)
❙ prey are rarely much larger than their predators:
❘ beyond a certain prey size, a predator cannot successfully subdue and consume the prey
❘ cooperative hunters are an exception, taking prey substantially larger than themselves
Form and Function Match Diet
❚ Form and function of predators are closely tied to diet:
❙ vertebrate teeth are adapted to dietary items:
❘ horses have upper and lower incisors used for cutting fibrous stems of grasses, flat-surfaced
molars for grinding
❘ deer lack upper incisors, simply grasping and tearing vegetation, but also grinding it
❘ carnivores have well-developed canines and knifelike premolars to secure and cut prey
More Predator Adaptations
❚ The variety of predator adaptations is remarkable:
❙ consider grasping and tearing functions:
37
❘ forelegs for many vertebrates
❘ feet and hooked bills in birds
❘ distensible jaws in snakes
❙ digestive systems also reflect diet:
❘ plant eaters feature elongated digestive tracts with fermentation chambers to digest long, fibrous
molecules comprising plant structural elements
Prey have adaptations for escaping their predators.
❚ Prey escape mechanisms are remarkably diverse:
❙ in animals:
❘ swift escape
❘ capability of early predator detection
❘ hiding or seeking refuge
❘ sensitive mechanisms for detecting predators
❙ in plants:
❘ thorns and defensive chemicals that dissuade herbivores
Crypsis and Warning Coloration
❚ Through crypsis, animals blend with their backgrounds; such animals:
❙ are typically palatable or edible
❙ match color, texture of bark, twigs, or leaves are not concealed, but mistaken for inedible objects
by would-be predators
❚ Behaviors of cryptic organisms must correspond to their appearances.
Warning Coloration
❚ Unpalatable animals may acquire noxious chemicals from food or manufacture these chemicals
themselves:
❙ such animals often warn potential predators with warning coloration or aposematism:
❘ predators learn to avoid such animals after unpleasant experiences
❘ certain aposematic colorations occur so widely that predators may have evolved innate aversions
Why aren’t all prey unpalatable?
❚ Chemical defenses are expensive, requiring large investments of energy and nutrients.
❚ Some noxious animals rely on host plants for their noxious defensive chemicals:
❙ not all food plants contain such chemicals
❙ animals utilizing such chemicals must have their own means to avoid toxic effects
Batesian Mimicry
❚ Certain palatable species mimic unpalatable species (models), benefiting from learning experiences
of predators with the models.
❚ This relationship has been named Batesian mimicry in honor of discoverer
Henry Bates.
❚ Experimental studies have demonstrated benefits to the mimic:
❙ predators quickly learn to recognize color patterns of unpalatable prey
❙ mimics are avoided by such predators
38
Müllerian Mimicry
❚ Müllerian mimicry occurs among unpalatable species that come to resemble one another:
❙ many species may be involved
❙ each species is both model and mimic
❙ process is efficient because learning by predator with any model benefits all other members of the
mimicry complex
❙ certain aposematic colors/patterns may be widespread within a particular region
Parasites have adaptations to ensure their dispersal.
❚ Parasites are usually much smaller than their hosts and may live either externally or internally:
❙ internal parasites exist in a benign environment:
❘ both food and stable conditions are provided by host
❙ parasites must deal with a number of challenges:
❘ host organisms have mechanisms to detect and destroy parasites
❘ parasites must disperse through hostile environments, often via complicated life cycles with
multiple hosts, as seen in Plasmodium, the parasite that causes malaria
Parasite-Host Systems: A Balancing Act
❚ The parasite-host interaction represents a balance between parasite virulence and host defenses:
❙ immune system of host can recognize and disable parasites
❙ but parasites may multiply rapidly before an immune response can be deployed
Parasites may defeat a host’s immune response.
❚ Circumventing the host’s immune system is a common parasite strategy:
❙ some parasites suppress the host’s immune system (AIDS virus)
❙ other parasites coat themselves with proteins that mimic the host’s own proteins (Schistosoma)
❙ some parasites continually coat their surfaces with novel proteins (trypanosomes)
Cross-Resistance
❚ Some parasites elicit an immune response from the host, then coat
themselves with host proteins before the immune response is fully mobilized:
❙ initial immune response by host may benefit the host later when challenged by related parasites in a
phenomenon known as cross-resistance
❚ Once an immune response has been elicited, antibodies can persist for a long time, preventing
reinfection.
Plants have antiherbivore defenses.
❚ Plant-herbivore “warfare” is waged primarily through biochemical means.
❚ Full spectrum of plant defenses includes:
❙ low nutritional content of plant tissues
❙ toxic compounds synthesized by the plants
❙ structural defenses:
❘ spines and hairs
❘ tough seed coats
❘ sticky gums and resins
Digestibility
❚ Animals typically select plant food according to its nutrient content:
❙ especially important to young animals, which have high demands for protein
❚ Some plants deploy compounds that limit the digestibility of their tissues:
❙ tannins produced by oaks and other plants interfere with the digestion of proteins
❙ some animals can overcome the effect of tannins through production of digestive dispersal agents
39
Secondary Compounds
❚ Secondary compounds are produced by plants for purposes (typically defensive) other than
metabolism.
❚ Such compounds can be divided into three major classes:
❙ nitrogen compounds (lignin, alkaloids, nonprotein amino acids, cyanogenic glycosides)
❙ terpenoids (essential oils, latex, plant resins)
❙ phenolics (simple phenols)
Induced and Constitutive Defenses
❚ Constitutive chemical defenses are maintained at high levels in the plant at all times.
❚ Induced chemical defenses increase dramatically following an attack:
❙ suggests that some chemicals are too expensive to maintain under light grazing pressure
❙ plant responses to herbivory can reduce subsequent herbivory
Herbivores control some plant populations.
❚ Examples of control of introduced plant pests by herbivores provides evidence that herbivory can
limit plant populations:
❙ prickly pear cactus in Australia ❘ controlled by introduction of a moth, Cactoblastis
❙ Klamath weed in California ❘ controlled by introduction of a beetle, Chrysolina
Effects of Grazers and Browsers on Vegetation
❚ Herbivores consume 30-60% of aboveground vegetation in grasslands:
❙ demonstrated by use of exclosures limiting access to vegetation by herbivores
❚ Occasional outbreaks of tent caterpillars, gypsy moths, and other insects can result in complete
defoliation of forest trees.
Summary 1
❚ Among consumers, ecologists recognize predators, parasitoids, and parasites.
❚ Predator-prey relative sizes may vary dramatically.
❚ Predators are well-adapted to capturing prey.
❚ Prey avoid predation by avoiding detection and by means of chemical, structural, and behavioral
defenses.
Summary 2
❚ Batesian mimicry involves an unpalatable model and palatable host.
❚ Müllerian mimicry complexes involve two or more unpalatable species that resemble one another.
❚ Parasites have unique adaptations for their way of life.
❚ Parasites and hosts remain in a delicate balance.
Summary 3
❚ Plants use structural and chemical defenses to deter herbivores.
❚ Some herbivores can detoxify secondary plant compounds, enabling them to consume otherwise
toxic species.
❚ Herbivores may control populations of plants at levels far below their sizes in the absence of
specialized consumers.
40
Background
❚ The behavior and, indirectly, life histories and ecological relationships of an individual are under
strong selective pressure from:
❙ the social and family environment
❙ relationship to members of both sexes
❚ For example, fitnesses of the male morphs of the side-blotched lizard are dependent on frequencies
of other male morphs in the population:
❙ these morphs interact through complex social interactions that determine reproductive success
Background
❚ Individuals interact with other members of the same species throughout their lives.
❚ Each individual must perceive the behaviors of others and make appropriate responses:
❙ some interactions pay benefits for cooperative behaviors because of a common interest:
❘ interactions with kin (common evolutionary heritage)
❘ interactions with mates (common interest in success of offspring)
Cooperation or Competition?
❙ All interactions between members of the same species delicately balance conflicting tendencies of
cooperation and competition, altruism and selfishness.
❙ Such a balance is evident in humans, the most social of animals:
❘ society is sustained by role specialization
❘ social life balances cooperation and conflict
What is Social Behavior?
❚ Social behavior includes all interactions among individuals of the same species.
❚ These interactions range from cooperation to antagonism.
❚ Consequences of these interactions for individuals are substantial, with effects on individual
fitness.
Territoriality
❚ Any area defended by an individual against the intrusion of others may be regarded as a territory:
❙ territories vary enormously in size and permanence
❙ animals are likely to maintain territories if:
❘ the resource is defensible
❘ the rewards outweigh the cost of defense
Dominance Hierarchies
❚ Defense of territories may not always be practical.
❚ In absence of territories, the outcome of conflict may be establishment of social rank.
❚ When individuals order themselves by social rank or status, the result is a dominance hierarchy.
❚ Social rank and occupancy of space may be directly related, as low-ranking individuals may be
relegated to the periphery of a flock.
To fight or not to fight?
❚ Establishment of territories or social rank depends on the outcome of contests between individuals.
❚ In any confrontation, participants must weigh:
❙ costs of fighting and benefits of winning
❙ likely outcome of the contest
❚ Determining optimal behavior is complicated by each individual’s lack of knowledge about the
behavior of the other participant.
41
Optimal Behaviors and Game Theory
❚ Game theory analyzes the outcomes of behavioral decisions when these outcomes depend on the
behavior of other players.
❚ Game theory predicts the individual’s behavior based the best estimates of:
❙ the other contestant’s response
❙ the reward for winning
Advantages and Disadvantages of Living in Groups
❚ True social groups result from a purposeful joining together of individuals.
❚ Living in groups results in benefits and costs to flocking birds, like the European goldfinch:
❙ benefit is less individual vigilance
❙ cost is the more rapid depletion of resources, forcing the flock to move more frequently
Natural selection balances the costs and benefits of behaviors.
❚ Toward a classification of behaviors:
❙ Most social interactions can be broken into acts performed by:
❘ donors - individuals initiating behaviors
❘ recipients - individuals toward whom behaviors are directed
A Classification of Behaviors
❚ Four combinations of fitness increments to donor and recipient lead to the
following classification:
❙ cooperation (benefits donor, selected for)
❙ selfishness (benefits donor, selected for)
❙ spitefulness (benefits no one, selected against)
❙ altruism (benefits recipient at cost to donor)
❚ Altruism, among these, is most problematic:
❙ selfish behaviors would be expected to prevail
❙ yet altruistic acts are common in social species
Kin selection favors altruistic behaviors.
❚ When an individual directs a behavior toward a sibling or other close relative, it influences the
fitness of an individual with whom it shares more genes than it does with an individual drawn at
random from the population.
❚ This special outcome of social behavior among relatives is called kin selection.
Identity by Descent
❚ The likelihood that two individuals share copies of any particular gene is the probability of identity
by descent, which varies by degree of relationship:
❙ also called the coefficient of relationship
❙ full sibs have a 50% probability of sharing any gene
❙ parents and children also have 50% probability of sharing any gene, etc.
A Model for Assessing Altruistic Behavior
❚ Total fitness of a gene responsible for a particular behavior is its inclusive
fitness:
❙ contribution to fitness of donor plus product of change in fitness to recipient X, weighted by
coefficient of relationship
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❙ a gene promoting altruistic behavior will have a positive inclusive fitness if:
C < Br where: C = cost to donor B = benefit to recipient r = coefficient of relationship
Implications of the Model
❚ Genes for altruistic behaviors should increase in the population when:
❙ behaviors have low cost to donor
❙ behaviors are restricted to close relatives
❚ Opportunities for evolution of altruistic behaviors do exist:
❙ individuals often associate in family groups
❙ individuals can often assess their relatedness
Cooperation among Individuals in Extended Families
❚ Complex relationships among extended human families are familiar to us:
❙ often such families include only one child-producing pair
❙ a portion of the behavior of non-nuclear members of the extended family are directed toward
well-being of these related children
Cooperation in Bee-Eaters
❚ Extended families of bee-eaters exhibit cooperative and competitive behaviors:
❙ selfish and selfless acts are directed toward others in direct accordance with the degree of
relationship
❙ inclusive fitness is the appropriate measure of selection on social behavior:
❘ altruistic behaviors can evolve among close relatives by kin selection
Cooperation Among Unrelated Individuals
❚ Social groups can form to promote mutual self-interest of unrelated individuals.
❚ Can groups of unrelated individuals move toward true cooperation?
Game Theory and Cooperation
❚ The paradox:
❙ conflict can reduce the fitness of selfish individuals below that of cooperative individuals, so
cooperative behaviors should evolve among unrelated individuals
❙ but, when most of a social group consists of cooperative individuals, a selfish individual can
achieve high fitness by cheating
The Hawk-Dove Game
❚ The hawk-dove game (prisoner’s dilemma):
❙ a hawk always competes over resources, taking all the rewards when it wins:
❘ the hawk strategy is not the best overall because hawks incur costs of conflict
❙ a dove never competes over resources, sharing resources with other doves, yielding them to hawks:
❘ the dove strategy is the best overall because resources are shared without costs of conflict
Hawks invade societies of doves.
❚ Dove behavior is not an evolutionarily stable strategy:
❙ a population of doves is easily invaded (from an evolution nary perspective) by hawkish behavior:
❘ a hawk in a population of doves reaps twice the rewards of doves
❙ a population of hawks is resistant to invasion by dove behavior, however
Can hawks and doves coexist?
❚ When the benefit is less than twice the cost of conflict, dove behavior can invade a population of
hawks.
❚ In this situation the proportion of hawks is one-half the ratio of the benefit to cost.
43
❚ Persistence of hawks and doves in this case is an evolutionarily stable mixed strategy.
Parents and offspring may come into conflict.
❚ Offspring consume parental resources, but this is desirable from the perspective of the parents:
when progeny thrive, so do the parents’ genes.
❚ Parents and offspring come into conflict when accumulation of resources by one offspring reduces
the overall fecundity of its parents.
Parents and offspring have different goals.
❚ Offspring try to resolve conflicts over resources in favor of their own reproductive success.
❚ For parents, a balanced approach to current and future reproduction is favored:
❙ resources allocated to one offspring cannot be allocated to another
❙ resources allocated to current offspring reduce those that can be allocated to future offspring
When does parent-offspring conflict occur?
❚ As young mature, the benefit to them of parental care declines.
❚ Because of coefficients of relationship among parents, an offspring, and that offspring’s sibs:
❙ when the benefit to parent of providing additional care falls below the cost of this care for future
reproduction, the parent should cease providing care
❙ offspring should continue to request additional care until the benefit to parent of providing that care
falls below twice the cost of this care for future reproduction Eusocial Insect Societies
❚ Social insects exhibit the extreme of family living, in which most offspring forego reproduction
and help their parents raise siblings.
❚ This situation raises evolutionary questions:
❙ how did such societies evolve?
❙ how can natural selection produce individuals with no individual fitness?
What is eusociality?
❚ Eusociality entails:
❙ several adults living together in groups
❙ overlapping generations
❙ cooperation in nest building and brood care
❙ reproductive dominance by one or a few individuals, including the presence of sterile castes
❚ Eusociality is limited among insects to Isoptera (termites) and Hymenoptera (ants, bees, wasps),
and to one mammal, the naked mole rat.
How did eusociality evolve?
❚ Potential sequence of evolutionary events:
❙ parents have a lengthened period of care for developing brood (parents guard brood or provision
larvae)
❙ parents live and continue to produce eggs after first progeny emerge
❙ offspring are in a position to help raise subsequent broods
❙ when progeny remain with their mother after adulthood, the way is open to relinquishing
reproductive function to support mother’s
Organization of Insect Societies
❚ Insect societies are dominated by one or a few egg-laying females, queens:
❙ queens of ants, bees, and wasps mate once and store sufficient sperm to produce a lifetime of
offspring
44
❚ Nonreproductive progeny of the queen:
❙ gather food and care for their developing brothers and sisters, some of which become sexually
mature and leave the nest to mate
❚ Specific details vary somewhat for termite colonies, which are headed by a king and queen.
Coefficients of Genetic Relationship in Hymenoptera
❚ Hymenoptera have a haplodiploid sex-determining mechanism:
❙ females (workers) develop from fertilized eggs
❙ males (drones) develop from unfertilized eggs
❚ Coefficients of genetic relationship are skewed:
❙ female worker to female sibling is 0.75
❙ female worker to male sibling is 0.25
❙ queen to son or daughter is 0.5
❚ Sex ratios are female-biased, 3:1.
Summary
❚ All behaviors have costs and benefits to the individual and to others affected by the behavior, with
special consequences for close relatives.
❚ Behavior is influenced by genetic factors and is thus subject to evolutionary
modification by natural selection.
❚ Interactions within a social setting lead to important evolutionary consequences when interests of
individuals conflict or coincide.
作业布置
课后小结
45
课
题
Lecture 5: Competition
学
时
4
教学目标
与要求
5.1 Consumers compete for resources
5.2 Failure of species to coexist in laboratory cultures led to competitive exclusion
principle
5.3 The theory of competition and coexistence is an extension of logistic growth models
5.4 Asymmetric competition can occur when different factors limit the populations of
competitors
5.5 Habitat productivity can influence competition between plant species
5.6 Competition may occur through direct interference
5.7 Consumers can influence the outcome of competition
重
点
5.1 Consumers compete for resources
5.2 Failure of species to coexist in laboratory cultures led to competitive exclusion
principle
5.3 The theory of competition and coexistence is an extension of logistic growth models
5.4 Habitat productivity can influence competition between plant species
5.5 Consumers can influence the outcome of competition
点
5.1Failure of species to coexist in laboratory cultures led to competitive exclusion
principle
5.2 The theory of competition and coexistence is an extension of logistic growth models
5.3 Asymmetric competition can occur when different factors limit the populations of
competitors
难
教学方法
与手段
讲授、讨论、多媒体
1、The economy of nature，6 th ed，Robert E. Ricklefs，2008 by W. H. Freeman and
Company；
2. General
Ecology, 2th ed., David T. Krohne. Thomson Learning, Inc.
ISBN
0-534-37528-6;
3. Ecology : Concepts and Applications 4th ed McGraw-Hill Companies, Inc. ;
参考资料
4. Ecology :From Individuals to Ecosystems,4th ed published 2006, Blackwell
Publishing;；
5.孙儒泳，李庆芬，牛翠娟，娄安如. 2002. 基础生态学. 高等教育出版社；
6.孙儒泳，李博，诸葛阳，尚玉昌编. 1992. 普通生态学. 高等教育出版社；
7. 李博主编. 1999. 生态学. 高等教育出版社；
8. 盛连喜主编，2005，
《环境生态学导论》，高等教育出版社。
46
教学内容及过程
Tansley’s Classic Study
❚ British ecologist A.G. Tansley was the first to experimentally demonstrate competition between
closely related species:
❙ he selected two species of the plant species Galium:
❘ G. saxatile is normally found on acid, peaty soils
❘ G. sylvestre is normally found on limestone hills and pastures
❙ these two species were grown alone and in mixture with the other species on both soil types in a
common garden
Tansley’s Results
❚ When grown alone in common garden experiments, each species performed better on its preferred
soil, although each could grow on the other soil type.
❚ When grown in mixture, each species overgrew and shaded the other on its preferred soil type.
❚ Tansley concluded that each species was at a disadvantage in competition when grown on the other
soil type; this helped explain the observed distributions of the two species in nature.
Tansley’s Conclusions
❚ Tansley’s conclusions have far-ranging implications for all competitive situations:
❙ the presence or absence of species can be determined by competition with other species
❙ conditions of the environment affect the outcome of competition
❙ competition may be felt very broadly throughout the community
❙ the present segregation of species may have resulted from past competition
What is competition?
❚ Competition is any use or defense of a resource by one individual that reduces the availability of
that resource to other individuals.
❚ Competition among individuals may be:
❙ intraspecific (within species)
❙ interspecific (between species)
Competition regulates populations.
❚ Intraspecific competition reduces resources in a density-dependent manner:
❙ underlies the regulation of population size is a process promoting evolutionary change
❚ Interspecific competition depresses populations of both competitors:
❙ may lead to elimination of one species, thus potentially important in determining coexistence
❙ gives the upper hand to the more efficient species
Consumers compete for resources.
❚ A resource is any substance or factor that is consumed by an organism and that supports increased
population growth as its availability in the environment increases:
❙ a resource is consumed
❙ a consumer uses a resource for its own maintenance and growth
❙ when resource availability is reduced, the result is reduced population growth
What is a resource?
❚ Resources include foods that are eaten, but also include:
❙ open space for sessile organisms
❙ hiding places and other safe sites
47
❚ Conditions are not resources:
❙ for example, temperature is not a resource:
❘ it may affect growth and reproduction, but is not consumed by organisms
Renewable and Nonrenewable Resources
❚ Nonrenewable resources are not regenerated:
❙ space is nonrenewable because, once occupied, it is unavailable
❚ Renewable resources are regenerated:
❙ animal foods and soil nutrients for plants are renewable because they are constantly regenerated
Kinds of Renewable Resources
❚ Some resources have sources external to the system, beyond the influence of consumers:
❙ sunlight and precipitation are examples
❚ Some resources are generated within the system and their abundances are depressed by consumers:
❙ the renewal rate of prey is reduced when predators reduce a prey population
❚ Some resources are generated within the system, but resource and consumer are linked indirectly:
❙ plants and soil nitrate are indirectly linked
Limiting Resources
❚ The potential of a resource to limit a population depends on availability relative to demand:
❙ this concept is embodied in Liebig’s law of the minimum:
❘ each population increases until the supply of some limiting resource becomes depleted
❘ this law applies strictly to resources that do not interact to determine population growth rate
Limitation by More Than One Resource
❚ Experiments with multiple resources on plant growth exhibit the difficulties with Liebig’s law:
❙ fertilized plants are better capable to respond to light than unfertilized plants
❙ various nutrients (e.g., nitrogen and phosphorus) interact in a synergistic fashion to promote plant
growth
The Competitive Exclusion Principle - Background
❚ Russian ecologist G.F. Gause conducted early experimental studies of competition:
❙ he grew Paramecium aurelia and P. caudatum alone and in mixture in nutritive media:
❘ each species grew well alone, but in mixture only P. aurelia persisted
❘ similar experiments conducted on a wide variety of species have tended to show the same thing one species persists and the other dies out, usually within 30-70 generations
The Competitive Exclusion Principle
❚ Results from many studies were summarized by Gause and others in the competitive exclusion
principle:
❙ two species cannot coexist indefinitely on the same limiting resource
❙ although similar species exist, careful study usually reveals that they differ in their habitat or diet
requirements
The Theory of Competition and Coexistence
❚ Mathematical models of competition were developed by A.J. Lotka and G.F.
Gause, based on the logistic equation:
1/N•dN/dt = r[K-N/K]
where: r = exponential rate of increase
N = population size
K = carrying capacity
t = time
48
Volterra’s model
❚ The Italian ecologist Vito Volterra incorporated interspecific competition into the logistic equation
as follows:
1/N1•dN1/dt = r1[(K1-N1-a1,2N2)/K1] where: subscripts 1 and 2 indicate the species a1,2 is the
competition coefficient -effect of species 2 on 1
The Competition Coefficient
❚ The competition coefficient in Volterra’s model expresses the degree to which each individual of
species 2 uses the resources of individuals of species 1:
❙ the extent to which this happens determines:
❘ effect of species 2 on species 1’s rate of growth
❘ effect of species 2 on the equilibrium population size of species 1 under interspecific competition
More on Competition Models
❚ Two models are needed to describe the joint effects of species upon one another.
❚ For two species to coexist, each population must reach a stable size greater than zero:
❙ dN1/N1dt = 0 when:
❘ N1 = K1 - á1,2N2
❙ dN2/N2dt = 0 when:
❘ N2 = K2 - á2,1N1
Coexistence
❚ At equilibrium, each competing species reduces the carrying capacity of the environment for the
other species.
❚ Coexistence is most likely when:
❙ the coefficients of interspecific competition are relatively weak (less than 1)
❘ this occurs when competitors share resources incompletely by partitioning resources among
themselves
Field studies demonstrate the pervasiveness of competition.
❚ Sequential introductions of biological control agents provide evidence for competitive exclusion
among species utilizing a limiting resource:
❙ various species of parasitoid wasps in the genus Aphytis have been introduced to control citrus
scale in California citrus groves:
❘ the earliest introduction, A. chrysomphali, was readily displaced by A. lingnanensis
❘ A. melinus subsequently displaced A. lingnanensis in all but the milder coastal areas
Plant competition differs between habitats.
❚ There are two conflicting proposals regarding the intensity of competition in different habitats that
differ in soil fertility:
❙ P.J. Grubb and D. Tilman have proposed that competition is increased when resources are scarce
(emphasis on below-ground competition for nutrients)
❙ J.P. Grime and P. Keddy have proposed that competition is reduced when resources are scarce
(emphasis on above-ground competition for light):
Grubb-Tilman versus Grime-Keddy Hypotheses
❚ Experimental studies of plant competition under conditions of varying soil resources have yielded
inconclusive results:
❙ for Stipa capensis in Israel, competition intensity increased with increasing resource availability
(soil moisture)
49
❙ for three prairie grasses in Minnesota, competition did not vary across a soil fertility gradient,
although competition shifted from below-ground in lownutrient plots to above-ground in high-nutrient
plots
Competition may occur through exploitation or interference.
❚ Exploitation competition occurs when individuals compete indirectly through their mutual effects
on shared resources:
❙ a common mechanism, typical of examples we’ve considered thus far
❚ Interference competition occurs when individuals defend resources through antagonistic behaviors:
❙ less common, requires that resources can be profitably defended
How does interference competition occur?
❚ Examples of interference competition range from territoriality to chemical warfare:
❙ hummingbirds exclude other hummingbirds (as well as bees and moths) from flowering plants
❙ encrusting sponges use poisonous chemicals to overcome other species of sponges
❙ shrubs release toxic chemicals that depress the growth of competitors
❙ bacteria and fungi also release poisonous chemicals in competitive interactions with other microbes
Allelopathy
❚ Allelopathy is chemical competition, most frequently reported among plants:
❙ typically mediated by toxic substances that cause direct harm to other individuals
❙ another example of allelopathy is the production of flammable oils by eucalyptus trees in Australia;
the oils promote frequent fires, which kill seedlings of competitors
An Example of Allelopathy
❚ Allelopathy has been reported in chaparral shrubs in southern California:
❙ several species of sage (Salvia) use chemicals to inhibit the growth of other vegetation:
❘ clumps of Salvia are often surrounded by bare areas separating the them from adjacent grasses
❘ Salvia gradually expands into the bare areas, pushing grasses further back
❘ toxic chemicals involved are likely volatile terpenes produced by the Salvia leaves ( the same
compounds give sage its quality as a spice)
Competition among Aquatic Animals
❚ Experimental studies of competition among intertidal barnacles by Joseph Connell have enhanced
our understanding of how competition can affect spatial distributions of species:
❙ barnacles are not food-limited, but compete intensely for limited space on rocks in the intertidal
zone:
❘ the barnacle Chthamalus is more tolerant of desiccation and thrives in the upper intertidal zone
❘ the barnacle Balanus is less tolerant of desiccation but can displace Chthamalus in the lower
intertidal zone
Competition Among Terrestrial Animals
❚ Interference competition (through aggressive behavior) has been observed among species of voles
(small mouse-like mammals) in the Rocky Mountain states:
❙ Microtus pennsylvanica and M. montanus inhabit wetter and drier habitats, respectively
❙ when either species was removed by trapping from its preferred habitat, the other species gradually
moved in
❚ Exploitation competition is much more common, although its effects are more difficult to identify.
50
Competition Between Distantly Related Species
❚ Darwin proposed that competition among closely related species (e.g., those belonging to the same
genus) should be more intense than competition among distantly-related species:
❙ although this is likely true, distantly-related species often utilize common resources:
❘ krill, shrimplike crustaceans of subantarctic waters, are fed upon by fish, squid, diving birds, seals,
and whales
❘ recent reductions in whales (by commercial exploitation) have resulted in expansions of seal and
penguin populations
The outcome of competition can be influenced by predators.
❚ Darwin noted that grazing can promote the coexistence of many species in grasslands:
❙ in the absence of grazers, dominant competitors grow rapidly and exclude other species
❚ Experiments by Robert Paine in the rocky intertidal have demonstrated the effect of predation in
reducing competitive exclusion:
❙ diversity of intertidal animals (barnacles, mussels, limpets, chitons) was approximately halved
when a key grazer (starfish Pisaster) was removed
Summary 1
❚ Competition is the use or defense of a resource by two or more consumers.
❚ Competition is usually for one or a few limited resources whose supply relative to demand is least.
❚ No two species of competitor can coexist on the same limiting resource.
Summary 2
❚ Mathematical models for competition build on the logistic growth model, but incorporate an
additional competition term.
❚ Competition can be easily demonstrated under laboratory conditions; carefully designed
experiments support the existence of competition in nature.
Summary 3
❚ Competition may be through exploitation or interference.
❚ Interference competition has been demonstrated in both aquatic and terrestrial organisms and may
be mediated by chemicals (allelopathy).
❚ Predators may alter the outcome of competition, promoting coexistence.
作业布置
课后小结
51
课
题
Lecture 6: Community Structure
学
时
4
教学目标
与要求
重
难
点
点
6.1 A biological community is an association of interacting populations
6.2 Measure of community structure include numbers of species and trophic levels
6.3 Feeding relationships organize communities in food webs
6.4 Food web structure influences the stability of communities
6.5 Communities can switch between alternative stable states
6.6 Trophic levels are influenced from above by predation and from below by production
Measure of community structure include numbers of species and trophic levels
Feeding relationships organize communities in food webs
Food web structure influences the stability of communities
Communities can switch between alternative stable states
Communities can switch between alternative stable states
Trophic levels are influenced from above by predation and from below by production
讲授、讨论、多媒体
教学方法
与手段
1、The economy of nature，6 th ed，Robert E. Ricklefs，2008 by W. H. Freeman and
Company；
2. General
Ecology, 2th ed., David T. Krohne. Thomson Learning, Inc.
ISBN
0-534-37528-6;
3. Ecology : Concepts and Applications 4th ed McGraw-Hill Companies, Inc. ;
参考资料
4. Ecology :From Individuals to Ecosystems,4th ed published 2006, Blackwell
Publishing;；
5.孙儒泳，李庆芬，牛翠娟，娄安如. 2002. 基础生态学. 高等教育出版社；
6.孙儒泳，李博，诸葛阳，尚玉昌编. 1992. 普通生态学. 高等教育出版社；
7. 李博主编. 1999. 生态学. 高等教育出版社；
8. 盛连喜主编，2005，
《环境生态学导论》，高等教育出版社。
52
教学内容及过程
What is a community?
❚ Ecologists have puzzled for almost a century over how to define a community,the assemblage of
species that occur together in the same place.
❚ Although ecologists agree that coexisting species interact strongly through consumer- resource and
competitive interactions, they do not agree about what a community is.
❚ two extreme views have dominated the debate over the nature of the community:
❙ F.E. Clements’s discrete unit
❙ H.A. Gleason’s loose assemblage of species
The Community View of Frederic E. Clements
❚ Clements saw the community as a superorganism in which the functions of various species are
connected like the parts of the body.
❚ Clements’s view included the following ideas:
❙ that component species had coevolved so as to enhance their interdependent unctioning
❙ that communities were discrete entities with recognizable boundaries
The Community View of Henry A. Gleason
❚ Gleason saw the community as a fortuitous association of species whose adaptations and
requirements enable them to live together under the particular conditions of a particular place.
❚ Gleason’s view included the following ideas:
❙ that component species occurred together largely by coincidence
❙ that there was no distinct boundary where one community meets another
Biological Communities
❚ every place on earth is shared by many coexisting organisms:
❙ these plants, animals, and microbes are linked to one another by their
feeding relationships and other interactions, forming a complex whole referred to as a biological
community:
❘ ecologists are uncertain as to the factors that determine the number of species that can coexist
Diverse Concepts of Community
❚ The holistic concept of Clements and others recognizes that we can only understand each species in
terms of its contributions to the dynamics of the entire system.
❚ The individualistic concept of Gleason and others recognizes that community structure and function
simply express the interactions of individual species, and do not reflect any organization above the
species level.
Community Concepts - A Middle Ground?
❚ An intermediate or mixed view of communities also exists, which:
❙ accepts the individualistic view that most interactions are antagonistic and that communities are
haphazard assemblages of species
❙ accepts the holistic premise that some attributes of communities arise from interactions among
species, reinforced through coevolution
Ecologists use several measures of community structure.
❚ One of the most widely used measures of community structure is the number of species it includes,
or species richness:
53
❙ this measure captures differences among tropical, temperate, and boreal regions:
❘ 16 km2 Barro Colorado Island in Panama supports 211 tree species, more than in all of Canada
❘ plots of 1 hectare in Amazonian Peru and Ecuador support more than 300 tree species
Ecologists use several measures of community structure.
❚ Because biological communities contain large numbers of species, it is helpful to partition diversity
into numbers of species at each trophic level (such as herbivores):
❙ within trophic levels, method or location of foraging distinguishes guilds of species (such as leaf
eaters within the herbivore trophic level)
❚ Patterns of relative abundance also permit ecologists to quantify structure of communities.
“Community” has many meanings.
❚ Community has a spatial definition:
❙ assemblages of plants and animals occurring in a particular locality and dominated by one or more
prominent species or some physical characteristic
❚ Community has a functional definition focusing on interactions:
❙ migrations of animals and linkages between terrestrial and aquatic systems
❙ ecological and evolutionary effects of all populations upon one another
A Natural Unit of Ecological Organization?
❚ The holistic view of communities predicts a closed community:
❙ the distributions of species are coincident
❙ the boundaries between communities (ecotones) are distinct
❚ The individualistic view of communities predicts an open community:
❙ the distributions of species are independent
❙ the boundaries between communities are diffuse
❚ Fire may sharpen the boundary between prairies and forests in the Midwestern U.S.
❙ perennial grasses resist fire damage, but fires cannot penetrate deeply into forests
The Continuum Concept 1
❚ Ecotones are less likely to form along gradients of gradual environmental change:
❙ the deciduous forest region of eastern North America does not fit the concept of the closed
community:
❘ few species have closely overlapping geographic ranges, tending to be independently distributed
❘ sharp ecotones are not found
❚ As ecologists sought to understand the ecology of the eastern forests, they turned to the continuum
concept.
The Continuum Concept 2
❚ The continuum concept embodies several key concepts:
❙ plants and animals replace one another continuously along environmental gradients
❙ species have different geographic ranges, suggesting independent evolutionary backgrounds and
ecological relationships
❙ because few species have broadly overlapping ranges, the assemblage of species found in any
particular place does not represent a closed community
Gradient Analysis
❚ A gradient analysis is usually undertaken by measuring the abundances of species and physical
conditions at a number of locations within a landscape:
54
❙ the abundances of species are then plotted as a function of the value of any physical condition
❚ Studies by R.H. Whittaker in the Great Smoky Mountains revealed few cases of distinct ecotones
between associations of species:
❙ species were distributed more or less independently over ranges of ecological conditions, with few
cases of consistent association between species
Feeding relationships organize communities in food webs.
❚ From an ecosystem perspective, species are usually combined into relatively few trophic levels:
❙ a food web analysis emphasizes the diversity of feeding relationships within an ecosystem:
❘ food web analysis thus has greater potential to differentiate community structure
❘ however, community structure is difficult to define, so different analyses may produce different
results
Does food web complexity lead to increased community stability?
❚ Food web complexity should lead to stability:
❙ when consumers have alternative resources, their populations depend less on fluctuations in any one
resource
❙ where energy can take many routes through the ecosystem, disruption of one pathway shunts more
energy through another
❚ But more diverse communities with many food web links may create pervasive, destabilizing time
lags in population processes!
How does food web structure affect community stability?
❚ Robert Paine and others who have studied food webs in natural communities have stressed the
importance of consumer-resource relationships in community organization:
❙ populations of keystone predators are particularly important in maintaining community stability and
diversity
There are different ways to portray food webs.
❚ Connectedness webs emphasize feeding relationships as links in a food web.
❚ Energy flow webs represent an ecosystem viewpoint, in which connections between species are
quantified by flux of energy.
❚ Functional webs emphasize the importance of each population through its influence on growth rates
of other populations.
When do communities have distinct boundaries?
❚ The concept of closed communities predicts discrete boundaries between communities:
❙ such boundaries should be expected under two circumstances in nature:
❘ when there is an abrupt transition in the physical environment
❘ when one species or life form dominates strongly, such that the edge of its range determines the
limits of many other species
Ecotones
❚ Ecotones represent boundaries between closed communities:
❙ such boundaries occur when there are sharp discontinuities in the physical environment:
❘ the interface between terrestrial and aquatic communities
❘ the boundary between soil types with contrasting properties (such as the boundary between
serpentine and nonserpentine soils)
Plants contribute to conditions maintaining ecotones.
❚ Transitions between broad-leaved and needle-leaved forests become more pronounced because of
conditions created by the plants themselves:
❙ increased soil acidity and greater accumulation of undecayed litter distinguishes the needle-leaved 55
forest
How does food web structure affect community stability?
❚ Is one particular arrangement of feeding relationships more stable than another?
❚ How important is food web stability to the structure of natural communities?
❚ These questions have proven difficult to answer:
❙ natural food webs vary tremendously, but each has persisted over long periods of time
❙ perhaps the rules governing community structure depend on particular circumstances of each system
Generalizations emerge from food web studies.
❚ Communities may be characterized by the number of species (richness) and number of feeding links
per species:
❙ the number of feeding links per species is independent of the species richness of the community
❙ the number of trophic levels and the number of guilds per trophic level increase with community
diversity
Trophic levels are influenced by predation and production.
❚ Alternative views of the effects of various trophic levels upon one another emphasize either
top-down control or bottom-up control:
❙ Hairston, Smith, and Slobodkin argued in 1960 that the “earth is green” because carnivores depress
the populations of herbivores that would otherwise consume most of the vegetation:
❘ this is a top-down perspective emphasizing a trophic cascade
Top-Down versus Bottom-Up Control
❚ Ecologists have debated the relative strengths of top-down versus bottom-up control mechanisms:
❙ is the earth green because plants resist consumption through various digestion inhibitors and toxic
substances?
❙ studies in lakes find evidence for both top-down and bottom-up control of community structure:
❘ primary production generally determines the sizes of higher trophic levels (bottom-up control), but
top-down interactions adjust these sizes within a narrower range
Species vary in relative abundance.
❚ One of the important differences among species within communities is their relative abundance:
❙ in most communities, a few species achieve dominance while most are rare, represented by relatively
few individuals
❙ ecologists have portrayed relative abundances in rank-order graphs, which reveal interesting
patterns:
❘ although such patterns have been modeled, such models have been most valuable as descriptive tools
rather than elucidating processes that determine relative abundance
Number of species increases with area sampled.
❚ Arrhenius first formalized the species-area relationship as:
S = cAz
where: S = number of species encountered A = area c and z are fitted constants
❚ After log transformation, the relationship is linear:
logS = logc + zlogA
Species-Area Relationships
❚ Analyses of many species-area relationships have shown that values of the slope, z, fall within the
range 0.20 - 0.35.
❚ Are species-area relationships artifacts of larger sample size (more individuals) in larger areas?
❙ comparisons of species numbers in different areas where samples of similar size were used still
56
reveals a species-area relationship
Predictable Species-Area Relationships
❚ Slopes of species-area curves vary in predictable ways:
❙ z-values are less for continental areas, greater for islands:
❘ rapid movement of individuals within continental areas prevents local extinction within small areas
Why do larger areas have more species?
❚ Larger areas have greater habitat heterogeneity.
❚ For islands, size per se makes the island a better target for potential immigrants from the mainland.
❚ Larger islands support larger populations, which persist because they have:
❙ greater genetic diversity
❙ broader distributions over habitats
❙ numbers large enough to prevent stochastic extinction
Diversity Indices
❚ Although species richness is a useful measure of biological diversity, it also has certain problems:
❙ the number of species encountered varies with the number of individuals inventoried
❙ species differ in abundance and thus in their functional roles in communities
❚ Diversity indices have addressed the second of these problems by weighting species by their relative
abundance...
Common Diversity Indices
❚ Simpson’s index is:
D = 1/Σpi 2
where: pi = the proportion of each species in the total sample
❚ Shannon-Wiener index is:
H = - Σ pilogepi
Properties of Diversity Indices
❚ Simpson’s index, D, can vary from 1 to S, the number of species in a sample:
❙ larger values of S indicate greater diversity
❙ when all species have equal abundances, D = S
❙ when species have unequal abundances, D < S
❙ rare species contribute less to the index than common ones
❚ The Shannon-Wiener index, like Simpson’s, takes on larger values with greater diversity:
❙ expressing Shannon-Wiener as eH scales the index to the number of species, making it more
comparable to Simpson’s
Rarefaction
❚ Richness values from samples of unequal size cannot be compared:
❙ rarefaction allows for comparisons, using a statistical procedure in which equal-sized subsamples are
drawn at random from the total sample:
❘ this portrays relationship of richness to sample size
❘ rarefaction was used by Howard Sanders to compare samples of benthic organisms
57
Summary 1
❚ A biological community is an association of interacting species.
❚ Ecologists consider community diversity and organization of species into guilds and food webs.
❚ Two competing concepts of community organization are holistic and individualistic, predicting
closed and open communities, respectively.
Summary 2
❚ In general, ecologists find that communities do not form discrete units.
Species tend to distribute themselves independently along environmental gradients in a pattern more
consistent with the open community concept.
❚ Ecologists have devised techniques of gradient analysis to study distributions of species with respect
to gradients of environmental conditions.
Summary 3
❚ Community structure can be summarized by means of food webs that emphasize various
relationships among species.
❚ Consumers can depress abundances in trophic levels below them in a trophic cascade or top-down
effect. Bottom-up effects occur when one trophic level affects productivity of higher trophic levels.
Summary 4
❚ In any community, some species are common and some are rare. Patterns of relative abundance have
been characterized, but their meanings are poorly understood.
❚ The number of species increases with the area sampled, more strongly so on islands.
❚ Various indices of diversity have been used to compare the number and
relative abundances of species between communities.
作业布置
课后小结
58
课
题
Lecture 7: Pathways of Elements in Ecosystems
学
时
4
教学目标
与要求
7.1 Energy transformations and element cycling are intimately linked
7.2 Ecosystems can be modeled as a series of linked compartments
7.3 Water provided a physical model of element cycling in ecosystems
7.4 Carbon cycle is closely tied to the flux of energy through the biosphere
7.5 Nitrogen assumes many oxidation states in its cycling through ecosystems
7.6 Phosphorus cycle is chemically uncomplicated
7.7 Sulfur exists in many oxidized and reduced forms
7.8 Microorganisms assume diverse roles in element cycles
重
点
Carbon cycle is closely tied to the flux of energy through the biosphere
Nitrogen assumes many oxidation states in its cycling through ecosystems
Phosphorus cycle is chemically uncomplicated
Sulfur exists in many oxidized and reduced forms
Microorganisms assume diverse roles in element cycles
点
Ecosystems can be modeled as a series of linked compartments
Carbon cycle is closely tied to the flux of energy through the biosphere
Nitrogen assumes many oxidation states in its cycling through ecosystems
Phosphorus cycle is chemically uncomplicated
Microorganisms assume diverse roles in element cycles
难
讲授、讨论、多媒体
教学方法
与手段
1、The economy of nature，6 th ed，Robert E. Ricklefs，2008 by W. H. Freeman and
Company；
2. General
Ecology, 2th ed., David T. Krohne. Thomson Learning, Inc.
ISBN
0-534-37528-6;
3. Ecology : Concepts and Applications 4th ed McGraw-Hill Companies, Inc. ;
参考资料
4. Ecology :From Individuals to Ecosystems,4th ed published 2006, Blackwell
Publishing;；
5.孙儒泳，李庆芬，牛翠娟，娄安如. 2002. 基础生态学. 高等教育出版社；
6.孙儒泳，李博，诸葛阳，尚玉昌编. 1992. 普通生态学. 高等教育出版社；
7. 李博主编. 1999. 生态学. 高等教育出版社；
8. 盛连喜主编，2005，
《环境生态学导论》，高等教育出版社。
59
教学内容及过程
Background
❚ Cycling of elements and flux of energy in ecosystems are fundamentally different:
❙ chemical elements are reused repeatedly
❙ energy flows through the system only once
❚ Many aspects of elemental cycling make sense only when we understand that chemical transformations
and energy transformations go hand in hand.
Assimilatory and Dissimilatory Processes
❚ Assimilatory processes:
❙ incorporate inorganic forms of elements into organic forms, requiring energy
❙ example: photosynthesis (reduction of carbon)
❚ Dissimilatory processes:
❙ transform organic forms of elements into inorganic forms, releasing energy
❙ example: respiration (oxidation of carbon)
Energy transformations and element cycling are linked.
❚ Organisms play important roles in cycling of elements when they carry out chemical transformations:
❙ most biological energy transformations are associated with biochemical oxidation and reduction of C, O,
N, and S
❙ these assimilatory and dissimilatory processes are often linked, one providing energy for the other
Coupled reactions are the basis of energy flow in ecosystems.
❚ A typical coupling of assimilatory/ dissimilatory reactions might involve:
❙ oxidation (dissimilation) of carbon in carbohydrate (energy-yielding), linked to
❙ reduction (assimilation) of nitrate-N to amino-N (energy-requiring)
❚ Some processes may involve many steps.
❚ Energy is lost at each step (inefficiency).
Ecosystems may be modeled as linked compartments.
❚ An ecosystem may be viewed as a set of compartments among which elements are cycled at various
rates:
❙ photosynthesis moves carbon from an inorganic compartment (air or water) to an organic compartment
(plant)
❙ respiration moves carbon from an organic compartment (organism) to an inorganic compartment (air or
water)
Elements move among compartments at different rates.
❚ Inorganic carbon released through respiration may be taken up quickly through photosynthesis. The
organic carbon fixed may be respired again quickly by plants.
❚ Organic carbon stored in deposits of coal, oil, or peat is not readily accessible and may remain in storage
for millions of years.
❚ Inorganic carbon may also be taken out of circulation for millions of years by precipitation as calcium
carbonate in aquatic systems.
A Physical Model for the Water Cycle
❚ The biosphere contains 1,400,000 teratons (TT, 1012 metric tons) of water, 97% of which resides in the
oceans.
60
❚ Other water compartments include:
❙ ice caps and glaciers (29,000 TT)
❙ underground aquifers (8,000 TT)
❙ lakes and rivers (100 TT)
❙ soil moisture (100 TT)
❙ water in atmosphere (13 TT)
❙ water in living things (1 TT)
The water cycle is solar-powered.
❚ The water cycle consumes one-fourth of the total solar energy striking the earth during a year:
❙ precipitation over land exceeds evaporation by 40 teratons/yr; surplus returns to the ocean in rivers
❙ evaporation over the oceans exceeds precipitation by 40 teratons/yr; surplus is delivered by winds to the
land masses
The residence time of water varies by compartment.
❚ The atmosphere contains 2.5 cm of moisture at any time; annual flux into and out of the atmosphere is 65
cm/yr:
❙ residence time is compartment size/flux, or 2.5 cm / 65 cm/yr = 0.04 yr, about 2 weeks.
❚ Soils, rivers, lakes and oceans have same flux rates as atmosphere, but they contain about 100,000 times
as much water, yielding a mean residence time of 2,800 yr.
The carbon cycle is linked to global energy flux.
❚ The carbon cycle is the focal point of biological energy transformations.
❚ Principal classes of carbon-cycling processes:
❙ assimilatory/dissimilatory processes (mainly photosynthesis and respiration)
❙ exchange of CO2 between atmosphere and oceans
❙ sedimentation of carbonates
Photosynthesis and Respiration
❚ Approximately 85 GT of carbon enter into balanced assimilatory/dissimilatory
transformations each year.
❚ Total global carbon in organic matter is about 2,650 GT (living organisms plus organic detritus and
sediments).
❚ Residence time for carbon in biological molecules = 2,650 GT / 85 GT/yr = 31 yr.
Ocean-Atmosphere Exchange
❚ Exchange of carbon across the atmosphere-ocean interface links carbon cycles of terrestrial and aquatic
ecosystems.
❚ Dissolved carbon pool is 30,000 GT, nearly 50 X that of atmosphere (640 GT).
❚ Net atmospheric flux (assimilation/ dissimilation and exchange with oceans) is
119 GT/yr for mean atmospheric residence time (640 GT / 119 GT/yr) of about 5 years.
Precipitation of Carbonates
❚ Precipitation (and dissolution) of carbonates occurs in aquatic systems:
❙ precipitation (as calcium and magnesium carbonates) leads to formation of limestone and dolomite rock
❘ turnover of these sediments is far slower than those associated with assimilation/dissimilation or
ocean-atmosphere exchange
❘ carbonate sediments represent the single largest compartment of carbon on planet (18,000,000 GT)
Precipitation of Calcium and Carbon Through the Ages
61
❚ CO2 dissolves in water to form carbonic acid, which dissociates into hydrogen, bicarbonate, and
carbonate ions:
CO2 + H2O _ H2CO3
H2CO3 ↔ H+ + HCO3 - ↔ 2H+ + CO32❚ Calcium ions combine with carbonate
ions to form slightly insoluble calcium
carbonate, which precipitates: Ca2+ + CO3 2- ↔ CaCO3
Slow Release of Sedimentary Calcium and Carbon
❚ Calcium removed from the water column in the oceans is replaced by calcium dissolved from limestone
sediments on land by slightly acidic water of rivers and streams.
❚ Carbon is also slowly released from oceanic sediments as limestone is subducted beneath continental
plates, and CO2 is outgassed in volcanic eruptions.
Reef-Builders extract carbon from water.
❚ In neutral conditions of marine ecosystems, extraction of CO2 from water column drives precipitation of
CaCO3: CaCO3 + H2O + CO2 ↔ Ca2+ + 2HCO3❚ Reef-building algae and coralline algae incorporate calcium carbonate into their hard structures, forming
reefs.
Changes in the Carbon Cycle Over Time
❚ Atmospheric CO2 concentrations have varied considerably over earth’s history:
❙ during the early Paleozoic era (550-400 Mya), concentrations were 15-20 X those at present
❙ concentrations declined to ca. present level by 300 Mya, then increased again to 5 X present level
through the early Mesozoic era (250-150 Mya) and have declined gradually since
❙ early Paleozoic and early Mesozoic eras were extreme greenhouse times,unlikely to be equaled by effects
of current human enhancement of atmospheric CO2
Nitrogen - A Most Versatile Element!
❚ Ultimate source (largest reservoir) of this essential element is molecular N2 gas in the atmosphere, which
can also dissolve in water to some extent.
❚ Nitrogen is absent from native rock.
❚ Nitrogen enters biological pathways through nitrogen fixation:
❙ these pathways are more complicated than those of the carbon cycle because nitrogen has more oxidized
and reduced forms than carbon
Ammonification
❚ Plants assimilate inorganic nitrogen into proteins, which may be passed through various trophic levels.
❚ Ammonification (dissimilation of N) is carried out by all organisms:
❙ initial step is breakdown of proteins into constituent amino acids by hydrolysis
❙ carbon (not nitrogen) in amino acids is then oxidized, releasing ammonia (NH3)
Nitrification
❚ Nitrification is oxidation of ammonia:
❙ first step is oxidation of ammonia to nitrite (NO2 -), carried out by Nitrosomonas in soil and
Nitrosococcus in oceans
❙ nitrite is then oxidized to nitrate (NO3 -) by Nitrobacter in soil and Nitrococcus in ceans
❙ nitrification is an aerobic process; the nitrifying organisms involved are chemoautotrophic bacteria
62
Denitrification
❚ Denitrification is the reduction of nitrate to nitric oxide (NO), which escapes as a gas:
❙ occurs in waterlogged, anaerobic soils, oxygen-depleted sediments, and bottom waters in aquatic
ecosystems
❙ carried out by heterotrophic bacteria such as Pseudomonas denitrificans
❙ further N-reductions may lead to production of nitrous oxide (N2O) and molecular nitrogen (N2), both
gases
❙ denitrification may be one of the principal causes of low availability of nitrogen in marine systems
Nitrogen Fixation
❚ Loss of nitrogen to atmosphere by denitrification is offset by nitrogen fixation:
❙ fixation is carried out by:
❘ free-living bacteria such as Azotobacter
❘ symbiotic bacteria such as Rhizobium, living in root nodules of legumes and other plants
❘ cyanobacteria
❙ N-fixation is an energy-requiring process, with energy supplied by oxidation of organic detritus
(free-living bacteria), sugars supplied by plants (bacterial symbionts), or photosynthesis (cyanobacteria)
Significance of Nitrogen Fixation
❚ Nitrogen fixation balances denitrification on a global basis:
❙ these fluxes amount to about 2% of total cycling of nitrogen through ecosystems
❚ Nitrogen fixation is often very important on a local scale:
❙ N-fixers dominate early colonizers on nitrogen-poor substrates, such as lava flows or areas left bare by
receding glaciers
The Phosphorus Cycle
❚ Phosphorous is an essential element, constituent of nucleic acids, cell membranes, energy transfer
systems, bones, and teeth.
❚ Phosphorus may limit productivity:
❙ in aquatic systems, sediments act as a phosphorus sink unless oxygendepleted
❙ in soils, phosphorus is only readily available between pH of 6 and 7
Phosphorus Transformations
❚ Phosphorus undergoes relatively few transformations:
❙ plants assimilate P as phosphate (PO4 3-) and incorporate this into organic compounds
❙ animals and phosphatizing bacteria break down organic forms of phosphorus and release the phosphorus
as phosphate
❙ phosphorus does not:
❘ undergo oxidation-reduction reactions in the ecosystem
❘ circulate through the atmosphere, except as dust
The Sulfur Cycle 1
❚ Sulfur is an essential element and, like nitrogen, has many oxidation states and follows complex
chemical pathways.
❚ Sulfur reduction reactions include:
❙ assimilatory sulfate reduction to organic forms and dissimilatory oxidation back to sulfate by many
organisms
❙ reduction of sulfate when used as an oxidizer for respiration by heterotrophic bacteria in anaerobic
environments
63
The Sulfur Cycle 2
❚ Sulfur oxidation reactions include:
❙ oxidation of reduced sulfur when used as an electron donor (in place of oxygen in water) by
photosynthetic bacteria
❙ oxidation of sulfur by chemoautotrophic bacteria that use the energy thus obtained for assimilation of
CO2
Sulfur in Coal and Oil Deposits
❚ Iron sulfide (FeS) commonly associated with coal and oil deposits can result in environmental problems:
❙ oxidation of sulfides in mine wastes to sulfate, which combines with water to form sulfuric acid,
associated with acid mine drainage
❙ oxidation of sulfides in coal and oil releases sulfates into atmosphere, which then form sulfuric acid, a
component of acid rain
Microorganisms assume diverse roles in element cycles.
❚ Decomposition in anaerobic organic sediments is dependent on certain specialized microbes, the
denitrifiers:
❘ these heterotrophic organisms use oxidized forms of N, S, and Fe as electron acceptors (oxidizers) in the
absence of oxygen
❘ for example, some anaerobic bacteria utilize nitrate as an alternative electron acceptor for the oxidation
of glucose: glucose + NO3 - _ CO2 + H2O + OH- + N2 + energy
Biological Nitrogen Fixation
❚ Biological nitrogen fixation (by bacteria and cyanobacteria) is essential to counterbalancing N losses
associated with denitrification.
❚ Nitrogen is often implicated as a limiting nutrient in terrestrial and aquatic systems.
❚ Nitrogen fixation is critical to ecosystem development in primary succession.
❚ Continued nitrogen input is essential for long-term health of natural ecosystems.
Autotrophic Diversity
❚ All autotrophs are capable of assimilating (reducing) carbon in CO2 into organic forms (initially
glucose):
❙ photoautotrophs accomplish this by capturing energy from sun through photosynthesis:
❘ green plants, algae, and cyanobacteria use water as an electron donor (reducing agent) and are aerobic
❘ purple and green bacteria use H2S or organic compounds as electron donors and are anaerobic
Chemoautotrophs
❚ Chemoautrophs are not photosynthetic, reducing inorganic carbon (from CO2), but using energy
obtained from aerobic oxidation of inorganic substrates:
❙ methane - Methanosomonas, Methylomonas
❙ hydrogen - Hydrogenomonas, Micrococcus
❙ ammonia - nitrifying bacteria Nitrosomonas, Nitrococcus
❙ nitrite - nitrifying bacteria Nitrobacter, Nitrococcus
❙ hydrogen sulfide, sulfur, sulfate - Thiobacillus
❙ ferrous iron salts - Ferrobacillus, Gallionella
Deep-Sea Vent Ecosystems
64
❚ Deep-sea vent ecosystems are far below the penetration of any light,
dependent on chemoautotrophic production:
❙ hot water coming from vents is charged with hydrogen sulfide, H2S
❙ chemoautrophic bacteria use oxygen from seawater to oxidize H2S, then use the energy thus obtained for
assimilatory carbon reduction
❙ other members of vent communities (clams, worms, crabs, fish) ultimately depend on primary production
of these bacteria
Living things are intimately involved in elemental cycles.
❚ Elements are cycled through ecosystems primarily because metabolic activities result in chemical
transformations.
❚ Each type of habitat presents a different chemical environment, especially with respect to:
❙ presence/absence of oxygen
❙ possible sources of energy
❚ Numerous adaptations have arisen to meet these challenges.
Summary 1
❚ Unlike energy, nutrients are retained in ecosystems and may cycle indefinitely.
❚ The movements of energy and elements, especially carbon, parallel one another in ecosystems.
❚ Energy transformations result from the coupled oxidation and reduction reactions of various elements.
Summary 2
❚ The water cycle is a physical analogy for element cycling in ecosystems; many elements are also
transported by the water cycle.
❚ The carbon cycle involves both biological and nonbiological processes fundamental to functioning of the
biosphere.
❚ The nitrogen cycle involves many transformations and oxidation states. Microorganisms play essential
roles throughout.
作业布置
课后小结
65
课
题
Lecture 8: Nutrient Regeneration in Terrestrial and Aquatic Ecosystems
学
时
4
教学目标
与要求
8.1 Weathering makes nutrients available in terrestrial ecosystems
8.2 Nutrient regeneration in terrestrial ecosystems occurs in the soil
8.3 Nutrient regeneration can follow many paths
8.4 Mycorrhizal associations of fungi and plant roots promote nutrient uptake
8.5 Climate affects pathways and rates of nutrient regeneration
8.6 In aquatic ecosystems, nutrients are regenerated slowly in deep water and sediments
8.7 Stratification hinders nutrient cycling in aquatic ecosystems • Oxygen depletion
facilitates regeneration of nutrients in deep waters
8.8 Nutrient inputs control production in freshwater and shallow- water marine
ecosystems
8.9 Nutrients limit production in the oceans
重
点
Nutrient regeneration in terrestrial ecosystems occurs in the soil
Nutrient regeneration can follow many paths
Mycorrhizal associations of fungi and plant roots promote nutrient uptake
In aquatic ecosystems, nutrients are regenerated slowly in deep water and sediments
Nutrient inputs control production in freshwater and shallow- water marine ecosystems
Nutrients limit production in the oceans
点
Weathering makes nutrients available in terrestrial ecosystems
Nutrient regeneration in terrestrial ecosystems occurs in the soil
Mycorrhizal associations of fungi and plant roots promote nutrient uptake
Nutrient inputs control production in freshwater and shallow- water marine ecosystems
难
讲授、讨论、多媒体
教学方法
与手段
1、The economy of nature，6 th ed，Robert E. Ricklefs，2008 by W. H. Freeman and
Company；
2. General
Ecology, 2th ed., David T. Krohne. Thomson Learning, Inc.
ISBN
0-534-37528-6;
3. Ecology : Concepts and Applications 4th ed McGraw-Hill Companies, Inc. ;
参考资料
4. Ecology :From Individuals to Ecosystems,4th ed published 2006, Blackwell
Publishing;；
5.孙儒泳，李庆芬，牛翠娟，娄安如. 2002. 基础生态学. 高等教育出版社；
6.孙儒泳，李博，诸葛阳，尚玉昌编. 1992. 普通生态学. 高等教育出版社；
7. 李博主编. 1999. 生态学. 高等教育出版社；
8. 盛连喜主编，2005，
《环境生态学导论》，高等教育出版社。
66
教学内容及过程
Acid Rain and Forest Growth
❚ Decline in forests, noted in northeastern US and central Europe in the 1960s, appeared correlated with
acid rain.
❚ The Clean Air Act of 1970 reduced emissions of sulfur oxides and particulates in the US.
❚ Forests did not show signs of recovery. Why?
Slow Recovery of Forests from Effects of Acid Rain
❚ Studies at Hubbard Brook Experimental Forest in New Hampshire showed why forests did not recover
after passage of Clean Air Act:
❙ acidity of rain declined slowly
❙ emissions of particulates declined, reducing an important source of calcium at Hubbard Brook
❙ leaching of calcium and other nutrients by acid rain left lasting effects on soil fertility
Lessons from Hubbard Brook
❚ Acidity itself is not the cause of tree death:
❙ long-term leaching of nutrients kills trees
❚ Natural recovery will be slow on nutrient-poor soils:
❙ restoration of nutrients will require weathering
❙ weathering is a slow process
More Lessons from Hubbard Brook
❚ Effects of acid rain on soils may remain for years, even if causes of the problem are addressed.
❚ Understanding nutrient cycling and regeneration is crucial to understanding ecosystem function.
Nutrient regeneration occurs in soils.
❚ Nutrients are added to the soil through weathering of bedrock or other parent material.
❚ How fast does such weathering occur?
❙ estimates can be made for positive ions such as Ca2+, K+, Na+, and Mg2+
❙ at equilibrium, net losses must be balanced by replenishment from weathering
Weathering of Ca2+ at Hubbard Brook
❚ Watershed budgets:
❙ precipitation inputs = 2 kg ha-1 yr-1
❙ streamflow losses = 14 kg ha-1 yr-1
❙ assimilation by vegetation = 9 kg ha-1 yr-1
❙ net removal thus = 21 kg ha-1 yr-1
❚ Total weathering of bedrock to offset Ca+2 losses is 1,500 kg ha-1 yr-1 or 1 mm depth.
❚ Later analyses showed this to be an overestimate; the system was not in equilibrium.
Quality of detritus influences the rate of nutrient regeneration.
❚ Weathering is insufficient to supply plants with essential elements (Ca, Mg, K, Na, N, P, S, etc.) at the
rates required.
❚ Rapid regeneration of these elements from detritus is essential for ecosystem function.
❚ In forests, detritus is abundant:
❙ includes plant debris, animal excreta, etc.
❙ >90% of plant biomass enters detritus pool
67
Breakdown of Leaf Litter
❚ Breakdown is a complex process:
❙ leaching of soluble minerals:
❘ 10-30% of substances in leaves are water-soluble
❙ consumption by large detritivores:
❘ assimilate 3-40% of energy
❘ macerate detritus, speeding microbial activity
❙ breakdown of woody components by fungi
❙ decomposition of residue by bacteria
Quality of Plant Detritus
❚ Litter of various species decays at different rates:
❙ weight loss in 1 yr for broadleaved species varied from 21% for beech to 64% for mulberry
❙ needles of pines and other conifers decompose slowly
❙ resistance to decay is largely a function of composition, especially lignins, which resist decay
❚ Fungi play special roles in degrading resistant materials:
❙ fungi especially capable of degrading cellulose, lignins Mycorrhizae
❚ Mycorrhizae are mutualistic associations of fungi and plant roots:
❙ endomycorrhizae - fungus penetrates into root tissue
❙ ectomycorrhizae - fungus forms sheath around root
❚ Mycorrhizae facilitate nutrient extraction from nutrient-poor soils, enhancing plant
production.
Function of Mycorrhizae
❚ Mycorrhizae are effective at extracting nutrients:
❙ penetrate larger volume of soil than roots alone
❙ secrete enzymes and acids, which extract nutrients
❚ Endomycorrhizae are associated with most plants:
❙ apparently an ancient association
❙ fungi are specialists at extracting phosphorus
❚ Ectomycorrhizae are also widespread:
❙ sheath stores nutrients and carbon compounds
❙ fungi consume substantial amount of net production
Climate and Nutrient Regeneration
❚ Nutrient cycling is affected by climate:
❙ temperate and tropical ecosystems differ because of effects of climate on:
❘ weathering
❘ soil properties
❘ decomposition of detritus
❚ In temperate soils, organic matter provides a persistent supply of mineral elements released slowly by
decomposition.
A Tropical Paradox
❚ Tropical forests are highly productive in spite of infertile soils:
❙ tropical soils are typically:
68
❘ deeply weathered
❘ have little clay
❘ do not retain nutrients well
❙ high productivity is supported by:
❘ rapid regeneration of nutrients form detritus
❘ rapid uptake of nutrients
❘ efficient retention of nutrients by plants/mycorrhizae
Slash-and-Burn Agriculture
❚ Cutting and burning of vegetation initiates the cycle:
❙ nutrients are released from felled and burned vegetation
❙ 2-3 years of crop growth possible
❙ fertility rapidly declines as nutrients are leached
❙ upward movement of water draws iron and aluminum oxides upward, resulting in laterite
Is Slash-and-burn sustainable?
❚ Traditional agriculture is sustainable:
❙ 2-3 years of cropping depletes soil
❙ 50-100 years of forest regeneration rebuilds soil quality
❚ Population pressures lead to acceleration of the cycle:
❙ soils are insufficiently replenished
❙ soils deteriorate rapidly, requiring expensive fertilizer subsidies
Vegetation and Soil Fertility
❚ Vegetation is critical to development and maintenance of soil fertility:
❙ clear-cutting of an experimental watershed at Hubbard Brook, NH resulted in:
❘ several-fold increase in stream flow
❘ 3- to 20-fold increase in cation losses
❘ shift from nitrogen storage to massive nitrogen loss:
• uncut system gained 1-3 kg N ha-1 yr-1
• clear-cut system lost 54 kg N ha-1 yr-1
Soil versus Vegetation Stocks of Nutrients
❚ Litter and other detritus do not form a large reserve of nutrients in the tropics:
❙ forest floor litter as percentage of vegetation plus detritus:
❘ 20% in temperate needle-leaved forests
❘ 5% in temperate hardwood forests
❘ 1-2% in tropical forests
❙ soil to biomass ratio for phosphorus in forests is 23.1 in Belgium, 0.1 in Ghana
Eutrophic and Oligotrophic Soils
❚ Tropics have both rich and poor soils:
❙ eutrophic (rich) soils develop in geologically active areas with young soils where:
❘ erosion is high
❘ rapid weathering of bedrock adds nutrients
❙ oligotrophic (poor) soils develop in old, geologically stable areas with old soils where:
❘ intense weathering of soils removes clay and reduces storage capacity for nutrients
69
Nutrient Retention by Vegetation
❚ Retention of nutrients by vegetation is crucial to sustained productivity in tropics.
❚ Plants retain nutrients by:
❙ retaining leaves
❙ withdrawing nutrients before leaves are dropped
❙ developing dense root mats near soil surface
Nutrients are regenerated from aquatic sediments.
❚ Soils and aquatic sediments share similar regenerative processes (both processes occur in aqueous
medium).
❚ Soils and aquatic sediments differ in two profound ways:
❙ release of nutrients in soils occurs near plant roots in soils, far from roots in sediments
❙ release of nutrients is aerobic in soils, anaerobic in aquatic sediments
Nutrients and Aquatic Productivity
❚ Productivity in aquatic systems is stimulated when nutrients are in the photic zone, resulting from
❙ proximity to bottom sediments
❙ upwelling of nutrient-rich water
❚ Regeneration of nutrients by excretion and decomposition may take place within the water column.
❚ Sedimentation represents a continual drain on nutrients within the water column.
Thermal stratification hinders vertical mixing.
❚ Vertical mixing is critical to replenishment of surface waters with nutrients from below:
❙ results from turbulent mixing driven by wind
❙ impeded by vertical density stratification:
❘ may be caused by thermal stratification
❘ also occurs when fresh water floats over denser salt water
❚ Vertical mixing has positive and negative effects on productivity:
❙ nutrients brought from depths stimulate productivity
❙ phytoplankton may be carried below photic zone
Stratification inhibits production.
❚ Thermal stratification in temperate lakes:
❙ nutrients regenerated in deeper waters cannot reach the surface
❙ vertical mixing in fall brings nutrient-rich water to the surface
❚ Stratification in other aquatic systems:
❙ arctic/subarctic and tropical lakes are not thermally stratified and mix freely
❙ in marine systems, stratified and non-stratified water bodies may meet, stimulating production
Nutrients limit production in the oceans.
❚ Primary production of marine ecosystems is tied closely to nutrient supplies:
❙ nitrogen is especially limiting
❙ shallow seas and areas of upwelling are especially productive
❙ some areas of open ocean are unproductive, despite adequate nitrogen and phosphorus:
❘ iron may be limiting in some areas of open ocean
❘ silicon may also be limiting, especially for diatoms
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Oxygen depletion facilitates nutrient regeneration.
❚ Nutrient regeneration is facilitated as anoxic conditions develop in hypolimnion and
sediments of stratified temperate lakes:
❙ nitrification ceases, leading to accumulation of ammonia
❙ iron is reduced from Fe3+ to Fe2+
❙ insoluble iron-phosphorus complexes are solubilized, releasing iron and phosphorus
❚ These processes reverse when oxidizing conditions return during fall overturn.
Phosphorus and Trophic Status in Lakes
❚ Phosphorus typically limits productivity in freshwater systems:
❙ P is especially scarce in well-oxygenated surface waters
❚ Natural lakes exhibit a wide range of fertilities:
❙ productivity depends on:
❘ external nutrient inputs
❘ internal regeneration of nutrients
Temperate lakes exhibit varied degrees of mixing.
❚ Productivity depends in part on degree of mixing of surface and deeper waters:
❙ shallow lakes may lack hypolimnion and circulate continuously
❙ somewhat deeper lakes stratify sporadically, with periods of mixing caused by:
❘ strong winds
❘ occasional cold weather in summer
❙ deepest lakes rarely mix completely, so productivity depends on external nutrient sources
Productivity varies in temperate lakes.
❚ Lakes may be classified on a continuum from oligotrophic to eutrophic.
❙ oligotrophic lakes are nutrient-limited and unproductive
❙ naturally eutrophic lakes exist in a well-nourished and productive dynamic steady-state
❙ human activities can lead to inappropriate nutrient loading resulting from:
❘ inputs of sewage
❘ drainage from fertilized agricultural lands
Cultural eutrophication of lakes is harmful.
❚ Nutrients stimulate primary production.
❚ Production is not inherently harmful, but:
❙ biomass accumulates, overwhelming natural regenerative processes
❙ untreated sewage also increases the amount of organic material in water
❙ increased biological oxygen demand depletes oxygen, killing fish and other obligate aerobes
Estuaries and marshes are highly productive.
❚ Shallow estuaries and salt marshes are among the most productive ecosystems on earth.
❚ High production in these systems results from:
❙ rapid and local regeneration of nutrients
❙ external loading of nutrients
Marshes and estuaries export their production.
❚ Adjacent marine ecosystems benefit from export of production from marshes and estuaries. For example,
❙ a Georgia salt marsh exported nearly 50% of its net primary production to surrounding marine systems in
the form of:
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❘ organisms
❘ particulate detritus
❘ dissolved organic material
Marshes and estuaries are critical to functioning of marine ecosystems.
❚ Marshes and estuaries are important feeding areas for larval and immature stages of fish and
invertebrates, providing:
❙ hiding places
❙ high productivity
❚ These organisms later complete their life cycles in the sea.
Summary
❚ Chemical and biochemical transformations are modified by physical and chemical conditions in each
type of ecosystem.
❚ Pathways of elements in ecosystems reflect patterns of nutrient cycling.
Summary: Terrestrial and Aquatic Systems
❚ In terrestrial systems:
❙ ecosystem metabolism is mostly aerobic
❙ production is limited by regeneration of nutrients from soils
❚ In aquatic systems:
❙ anaerobic respiration and regeneration of nutrients occurs in sediments, far from producers
❙ local regeneration of nutrients occurs in water column
❙ productivity is ultimately limited by regeneration of nutrients from deeper waters
作业布置
课后小结
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