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CHAPTER 50
AN INTRODUCTION TO ECOLOGY
AND THE BIOSPHERE
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. Explain why the field of ecology is a multidisciplinary science.
2. Describe the relationship between ecology and evolution.
3. Explain the importance of temperature, water, light, soil, and wind to living organisms.
4. Describe how environmental changes may produce behavioral, physiological,
morphological, or adaptive responses in organisms.
5. Describe the characteristics of the major biomes: tropical forest, savanna, desert, temperate
grassland, temperate forest, taiga, tundra.
6. Using a diagram, identify the various zones found in the marine environment.
ANSWERS:
1. It involves abiotic factors as well as biotic ones. Thus Chemistry as well as physics enters into
the
picture. Living things are subject to changes in the geology and chemistry of the Earth as well
as
physical factors like the weather.
2. It was the geographical distribution of organisms and their exquisite adaptations to specific
environments that proved Charles Darwin with evidence for evolution. Thus, events that occur
in
the frame of what is sometimes called ecological time translate into effect over the longer scale
of
evolutionary time.
3. Temperature: is important because of the effects on the biological processes and the inability
of
most organisms to regulate body temperature precisely.
Water: is important because it is essential to life but its availability varies dramatically among
habitats.
Sunlight: provides the energy that drives nearly all ecosystems, although only Plants and
other
photosynthetic organisms use this energy source directly.
Soil: the composition limits the distribution of plants and the animals that feed upon them,
thus
contributing to the patchiness we see in terrestrial biomes.
Wind: amplifies the effects of environmental temperature on organisms by increasing heat
loss due
the evaporation and convection.
4. Behavioral: The quickest response of many animals to an unfavorable change in the
environment is
to move to a new location. Such movements may be fairly localized.
Physiological: generally slower than behavioral. Relatively small changes in the rate of
process, and
that do not require changes of morphology or biochemical pathways, can occur very rapidly. Ex:
when you go out on a very cold day and your blood vessels constrict within seconds ,
minimizing
the loss of body heat.
Morphological: organisms may react to some change in the environment with responses that
alter
the form of internal anatomy of the body. Ex: some birds grow a thicker coat in the winter than in
the summer.
Adaptation: behavioral, physiological, and morphological mechanisms we have examined are
responses of individual organisms operating on an ecological time scale. These responses
occur
within a framework of adaptations fashioned by natural selection acting over evolutionary time.
5. Tropical rain forest: High temperature and heavy rainfall. Vegetation consists of tall trees that
branch only at their tops, forming a spreading canopy that allows little light to reach the forest
floor. Epiphytes (plants that live on other trees) and vines commonly grow on trees, but due to
lack of light, little grows on forest floors.
Savannas: grasslands with scattered trees. Because savannas are tropical, they are subject
to high temperatures. However, they receive considerably less water than rain forests.
Temperate Grasslands: receive less water and are subject to lower temperatures than are
savannas. The North American prairie is an example.
Temperate deciduous forest: occupy regions that have warm summers, cold winters, and
moderate precipitation. Deciduous trees shed their leaves during the winter, an adaptation to
poor growing conditions.
Deserts: hot and dry. Growth of annual plants is limited to short periods following rains. Other
plants adapted to the hostile conditions, for example cacti. Many animals have thick skins,
conserve water by producing no urine or very concentrated urine, and restrict their activity to
nights.
Taiga: coniferous forests( pines, firs and other trees with needles for leaves). Winters are
cold, and precipitation is in the form of snow.
Tundras: winters so cold that the ground freezes. During the summer the upper topsoil thaws,
but the deeper soil, the permafrost, remains permanently frozen. During the summer the melted
topsoil supports a grassland type community consisting of grasses, sedges, and other
vegetation tolerant of soggy soils.
6. Figure 46.26
CHAPTER 52
POPULATION ECOLOGY
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. Define the scope of population ecology.
2. Distinguish between density and dispersion.
3. Explain how ecologists measure density of a species.
4. Explain how age structure, generation time, and sex structure of populations can affect
population growth.
5. Describe the characteristics of populations that exhibit Type I, Type II, and Type III
survivorship curves.
6. Explain how density-dependent factors affect population growth.
7. Describe how weather and climate can function as density-independent factors in controlling
population growth.
8. Explain how density-dependent and density-independent factors may work together to control
a population's growth.
9. List the three major characteristics of a life history and explain how each affects the:
a. Number of offspring produced by an individual
b. Population's growth
10. Explain how predation can affect life history through natural selection.
11. Distinguish between r-selected populations and K-selected populations.
ANSWERS:
1. The Key concepts of Population Ecology are basically:
density and the spacing of individuals
Demography the study of factors that affect birth and death rates.
Traits that affect schedules of reproduction and death; life history.
Mathematical mode for exponential growth describes an idealized population in an unlimited
environment.
A logistic model of population growth incorporates the concept of carrying capacity.
Both density-dependant and density-independent factors can affect population growth.
The human population has been growing exponentially for centuries but will not be able to do so
indefinitely.
2. Density is the number of individuals per unit area or volume, where as Dispersion,
Is the pattern of spacing among individuals within the geographical boundaries of the
population.
3. Ecologist often use a variety of sampling techniques to estimate densities and total population
sizes. Such estimates are more accurate when there are more numerous or larger sample plots,
and when the habitat is homogeneous. In some cases, population sizes are estimated by
indirect indicators, such as the number of nests or burrows or signs such as droppings or tracks.
Another one is the Mark-recapture method.
4. The age structure affects population growth because pretty much, a population with a large
percentage of individuals of prime reproductive age will grow proportionally faster than a
population that has an age structure skewed towards older individuals. When it comes to
generation time, a shorter generation time will result in faster population growth. This is simply
because the increase in population size attributed to births accumulate more rapidly when
individuals reach sexual maturity in a shorter period of time. Finally with sex ratio, the number of
females is usually directly related to the number of births that can be expected, but the number
of males may be less significant because in many species, a single male can mate with several
females.
5. A Type I curve is relatively flat at the start, reflecting low death rates during early and middle
life, dropping steeply as death rates increase among older age groups. Type II curves are
intermediate, with mortality more constant over the life span. Type III curve drops sharply at the
left of the graph, reflecting very high death rates for the young, but then flattens out as death
rates decline for those few individuals that have survived to a certain critical age.
6. Density-dependant factors reduce the population growth rate by decreasing reproduction or
by increasing mortality in a crowded population.
7. For example, a freeze in the fall may kill a certain percentage of the insects in a population.
Obviously, the timing of the first freeze, and just how cold it gets is not affected by the density
of the insect population.
8. In some cases density dependant and independent can work together to regulate a
population. For example, in very cold and snowy areas, many deer may starve to death during
the winter.
9. …
10. …
11. k-selected populations, also called equilibrial populations, are those that are likely to be
living at a density near the limit imposed by their resources. By contrast, r-selected populations,
also called opportunistic populations, are likely to be found in variable environment in which
population densities fluctuate, or in open habitats where individuals are likely to face little
compensation.
CHAPTER 53
COMMUNITY ECOLOGY
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. Explain the relationship between species richness, relative abundance, and diversity.
2. List four properties of a community, and explain the importance of each.
3. Explain how interspecific competition may affect community structure.
4. Distinguish between an organism's fundamental niche and realized niche.
5. Explain the role of predators in community structure.
6. Distinguish among parasitism, mutualism, and commensalism.
7. Distinguish between primary succession and secondary succession.
ANSWERS:
1. Species richness is the number of species the community contains. Relative abundance is
basically the fact that some communities consist of a few common species and many rare ones,
whereas others contain an equivalent number of species that are all about equally common.
Finally, Species diversity considers both components of diversity: species richness and relative
abundance.
2. Stability: is the tendency of a community to reach and maintain an equilibrium, or relatively
constant condition, in the face of disturbance.
Community Resilience: the ability of a community to persist in the face of disturbance, is related
to stability but does not imply stability on the individual populations that compose the
community.
Competition: major factor limiting the diversity of species that could occupy a community.
Predation: predators always reduce the diversity of species in communities.
3. Interspecific competition is when two or more species in a community rely on similar limiting
resources. The density-dependant effects of interspecific competition are, as population
densities increase, every individual has access to a small share of limiting resources; as a
result, mortality rates increase, birth rates decrease and population growth is curtailed.
4. The term fundamental niche refers to the set of resources a population is theoretically
capable of using under ideal circumstances. While, the resources a population actually uses are
collectively called its realized niche.
5. Predators moderate competition among its prey species.
6. In parasitism, one organism, the parasite harms the host; in commensalism, one partner
benefits without significantly affecting the other; and in mutualism, both partners benefit from the
relationship.
7. The process of primary succession begins in an essentially lifeless area where soil has not
yet formed, such as on a volcanic island, or on the rubble left behind by a retreating glacier.
Then, over a process of 200 years, plants start growing.
Secondary succession occurs where an existing community has been cleared by some
disturbance that leaves the soil intact. Often the area begins a return to something like its
original state.
CHAPTER 54
ECOSYSTEMS
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. Explain the importance of autotrophic organisms with respect to energy flow and nutrient
cycling in ecosystems.
2. List and describe the importance of the four consumer levels found in an ecosystem.
3. Explain how gross primary productivity is allocated by the plants in an ecosystem.
4. Explain why productivity declines at each trophic level.
5. Distinguish between energy pyramids and biomass pyramids.
6. Describe the carbon cycle, and explain why it is said to result from the reciprocal processes
of photosynthesis and cellular respiration.
7. Describe the nitrogen cycle, and explain the importance of nitrogen fixation to all living
organisms.
8. Explain how phosphorus is recycled locally in most ecosystems.
9. Describe how increased atmospheric concentrations of carbon dioxide could affect the Earth.
10. Describe how human interference might alter the biosphere.
ANSWERS:
1. Each ecosystem has a trophic structure of feeding relationships that determines the pathways
of energy flow and chemical cycling. The trophic level that ultimately supports all others consists
of autotrophs, or the primary producers of the ecosystem most producers are photosynthetic
organisms that use light energy to synthesize sugars and other organic compounds, which they
then use as fuel for cellular respiration and as building material for growth.
2. Herbivores, which eat plants or algae, are the primary consumers. The next trophic level
consists of secondary consumers, carnivores that eat herbivores. These carnivores may in turn
be eaten by other carnivores that are tertiary consumers, and some ecosystems have
carnivores of an even higher level called Quaternary consumers.
3. The amount of light energy converted to chemical energy by autotrophs of an ecosystem
during a given time is called primary productivity. Total primary productivity is known as gross
primary productivity. Gross primary productivity results from photosynthesis; net primary
productivity is the difference between the yeild of photosynthesis and the consumption of
organic fuel in respiration.
4. Gross Primary productivity is a result of photosynthesis.
5. The multiplicative loss of energy from a food chain can be represented diagrammatically by a
pyramid of productivity, in which the trophic levels are stacked in blocks, with primary producers
forming the foundation of the pyramid. One important ecological consequence of decreasing
energy transfers through a food web can be represented in a biomass pyramid, in which each
tier represents the standing crop biomass (the total dry weight of all organisms) in a trophic
level.
6. Carbon is a basic constituent of all organic compounds. Is in: atmosphere as carbon dioxide,
fossil fuels (coal and oil), peat, durable organic material (cellose). Assimilation: plants use CO2
in photosynthesis; animals consume plants or other animals. Release: plants and animals
release CO2 through respiration and decomposition; CO2 is released when organic materials
such as wood and fossil fuels are burned.
7. Nitrogen is required for the manufacture of all amino acids and nucleic acids. Reservoirs:
atmosphere (N2); soil (NH4+ or ammonium, NH3 or ammonia, NO2- or nitrite, NO3- or nitrate).
Assimilation: plants absorb nitrogen either as NO3- or as NH4+; animals obtain nitrogen by
eating plants or other animals. The stages in the assimilation of Nitrogen are as follows:
Nitrogen Fixation: N2 to NH4+ by prokaryotes (in soil and root nodules); N2 to NO3- by lightning
and UV radiation.
Nitrification: NH4+ to NO2- and NO2- to NO3- by various nitrifying bacteria. NH4+ or NH3- to
organic compounds by plant metabolism.
Release: denitrifying bacteria convert NO3- back to N2 (denitrification); detrivorous bacteria
convert organic compounds back to NH4+ (ammonification); animals excrete NH4+ (or NH3),
urea, or uric acid.
8. Well, plants absorb inorganic PO4 3- (phosphate) from soils, and they release phosphorus
when they decompose. On the other hand, animals obtain phosphorus when they eat plants or
other animals and they release it when they excrete their wastes or decompose.
9. Increased productivity by vegetation is one predictable consequence of increasing CO2
levels. Another consequence would be the long-term effects of rising atmospheric CO2
concentration in the atmosphere which influences the Earth’s heat budget, this would increase
the temperature level causing ice at the poles to melt and raise the sea level an estimate of
100m, gradually flooding coastal areas 150 km from the current coastline inward.
10. Humans interference might alter the biosphere by the moving of certain nutrients. They
could in turn affect the balance of these nutrients in the certain biospheres in which they are
found. Such as taking away to much from one and adding in to much to another leaving it
unbalanced as I stated before.