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FUNDAMENTALS OF
ECOLOGY
Chapter Outline
THE STUDY OF ECOLOGY
ECOLOGY AND THE PHYSICAL
ENVIRONMENT
The Environment
Habitat: Where an Organism Lives
Maintaining Homeostasis
Homeostasis and the Distribution of
Marine Organisms
Characteristics of the Abiotic
Environment
Sunlight
Temperature
Salinity
Pressure
Metabolic Requirements
Metabolic Wastes
POPULATIONS
Population range and size
Distribution of Organisms in a
Population
Changes in Population Size
Survivorship
Life History
Population Growth
Population Regulation
Niche: An Organism’s Environmental
Role
Connell’s Barnacles
Biological Interactions
Competition
Predator-Prey Relationships
Symbiosis: Living Together
ECOSYSTEMS: BASIC UNITS OF THE
BIOSPHERE
Energy Flow through Ecosystems
Producers
Measuring Primary Productivity
Consumers
Food Chains and Food Webs
Other Energy Pathways
Trophic Levels
Ecological Efficiency
Trophic Pyramids
Biogeochemical Cycles
Hydrologic Cycle
Carbon Cycle
Nitrogen Cycle
THE BIOSPHERE
Distribution of Marine Communities
and Ecosystems
Pelagic Division
Benthic Division
KEY CONCEPTS
ARE YOU STILL WONDERING?
QUESTIONS FOR REVIEW
SUGGESTIONS FOR FURTHER READING
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Chapter Objectives
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Recognize the scope and scale of ecology as it pertains to marine environments.
Identify the abiotic factors that constrain marine organisms.
Define population.
Explain the different measurements of populations that scientists use and what
those measurements tell scientists.
Compare and contrast logistic and exponential growth.
Compare and contrast density-dependent and density-independent factors for
population regulation.
Define niche and recognize the difference between a fundamental and realized
niche.
Identify the various ways that organisms may interact in a marine community.
Diagram energy flow through an ecosystem.
Define food web, primary productivity, trophic level, and energy pyramid.
Describe the hydrologic, carbon, and nitrogen cycles, including how humans
have disrupted these cycles.
Key Terms
ecosystem
biosphere
environment
abiotic factors
biotic factors
habitat
microhabitat
homeostasis
optimal range
stress zone
zone of tolerance
phytoplankton
desiccant
ectotherms
endotherms
metabolism
salinity
solutes
osmosis
nutrients
limiting nutrients
anaerobic organisms
aerobic organisms
eutrophication
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Fundamentals of Ecology
algal bloom
population
geographic range
sampling methods
mark-recapture method
population density
dispersion
clumped pattern
uniform pattern
random pattern
generation time
survivorship
survivorship curve
Type I survivorship
curve
Type II survivorship
curve
Type III survivorship
curve
life history
clutch size
biological fitness
recruitment
larval settlement
exponential growth
logistic growth
carrying capacity
density-dependent
factor
density-independent
factor
r-strategist
K-strategist
community
niche
fundamental niche
realized niche
interspecific
competition
intraspecific
competition
competitive exclusion
resource partitioning
herbivores
carnivores
keystone species
symbiosis
mutualism
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commensalism
parasitism
parasite
host
photosynthesis
autotroph
primary productivity
light-dark-bottle
method
heterotroph
first-order (primary)
consumers
second-order
(secondary)
consumers
third-order (tertiary)
consumers
omnivores
detritivores
detritus
decomposers
food chain
food web
dissolved organic
matter (dom)
trophic level
ecological efficiency
ten percent rule
energy pyramid
pyramid of biomass
pyramid of numbers
biogeochemical cycle
precipitation nuclei
pelagic division
water column
benthic division
neritic province
oceanic province
photic zone
disphotic (twilight) zone
aphotic zone
plankton
nekton
neuston
intertidal zone
shelf zone
bathyal zone
abyssal zone
hadal zone
epifauna
infauna
Chapter Summary
1. An organism’s environment consists of all the external factors acting on that
organism. Organisms expend energy to maintain homeostasis, a relatively constant
environment for their cells. Characteristics of the physical environment determine
the amount of energy necessary to maintain homeostasis.
2. In ecological terms, a population is a group of the same species that occupies a
specific area. Factors that affect reproduction and mortality rate, such as
survivorship and life histories, have a significant effect on the size of populations.
Populations grow when more organisms are added through reproduction and
immigration than are lost through death and emigration. Characteristics of the
environment, such as space and available food, limit the number of organisms an
area can support. The carrying capacity is set by density-dependent or densityindependent factors.
3. A community is composed of populations of organisms that occupy the same habitat
at the same time. The role an organism plays in its environment, in a sense its
“profession,” is its niche. Interactions with other organisms and the physical
environment, however, limit it to a smaller part of the niche called its realized niche.
4. Although energy constantly flows through ecosystems, nutrients necessary for life
are constantly recycled. Producers capture the energy of sunlight in the chemical
bonds of organic molecules. Consumer organisms rely on these molecules as a
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source of food because they cannot synthesize their own. The complex feeding
networks that result are known as food webs. The energy that an organism receives
from photosynthesis or from feeding on other organisms is temporarily stored until
the organism is consumed by another or decomposed. Energy transfer from one
trophic level to the next is not efficient.
5.
The biosphere contains all of the Earth’s communities and ecosystems. Estuaries,
rocky coasts, sandy shores, salt marshes, mangrove swamps, kelp forests, and coral
reefs are some examples of marine communities and ecosystems. Ecologists divide
the marine environment into two major divisions: the pelagic division, composed of
the ocean’s water (the water column), and the benthic division, the ocean bottom. These
divisions can be subdivided into zones on the basis of distance from land, light availability,
and depth.
Chapter Outline
I.
Study of Ecology
A. Ecology, ecosystems, and biospheres.
1. Energy flows through the ecosystems in the biosphere.
2. Nutrients cycle through biosphere ecosystems.
II. Ecology and the Physical Environment
A. The environment.
1. Abiotic factors.
a. Temperature.
b. Salinity.
c. pH.
d. Sunlight.
e. Ocean currents.
f. Wave action.
g. Sediments.
2. Biotic factors.
B. Habitat: where an organism lives.
1. Marine habitats include (but are not limited to):
a. Rocky shores.
b. Sandy shores.
c. Mangrove swamps.
d. Coral reefs.
e. Deep-sea vents.
2. Marine habitats are unique and characterized by specific abiotic factors that define
their worldwide distribution.
3. Microhabitats: small subdivisions within a larger habitat.
C.
Maintaining homeostasis.
1. Homeostasis: internal balancing of factors in response to changing external
conditions.
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a. Changes in external environment such as temperature, salinity, and dissolved
oxygen require marine organisms to adapt in order to survive.
2. Physiological mechanisms and behavioral adaptations for maintaining
homeostasis.
3. Homeostasis and the distribution of marine organisms.
a. Optimal range.
b. Zones of stress.
c. Zones of intolerance.
D. Characteristics of the abiotic environment.
1. Physical environment: Physical parameters of marine ecosystems determine the
biological communities found in the ecosystem.
2. Sunlight: The amount of sunlight in an ecosystem determines how much
photosynthetic activity (food production) occurs in that ecosystem.
a. Phytoplankton.
b. Vision.
c. Desiccation.
3. Temperature: Surface water temperature varies less than ambient air
temperature; temperature variation impacts marine organisms living in intertidal
areas.
4. Salinity.
a. Solutes.
b. Osmosis.
c. Salt and water balance.
5. Water pressure: Water pressure increases one atmosphere (760 mm Hg) for every
10 meters of water depth.
6. Metabolic requirements: All organisms require nutrients to survive and grow.
a. Nutrients.
b. Limiting nutrients.
c. Anaerobic organisms (anaerobes).
d. Aerobic organisms (aerobes).
e. Eutrophication.
7. Metabolic wastes: All organisms produce waste as a result of metabolism.
III. Populations
A. Population range and size.
1. Geographical range.
2. Sampling method.
B. Population density.
1. Dispersion.
a. Uniform distribution.
b. Random distribution.
c. Clumped distribution.
C. Changes in population size.
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1.
IV.
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Population size increases as a result of births (natality) and immigration (new
organisms joining the population from other populations).
2. Population size decreases due to deaths (mortality) and emigration (organisms
leaving the population to join different populations).
3. Survivorship: the relationship between age and mortality; this relationship is
frequently illustrated using a graph in which age is the independent variable (xaxis) and population size is the dependent variable (y-axis).
a. Type I survivorship curve: Mortality is greatest at the end of the life span of the
species.
b. Type II survivorship curve: Mortality is constant throughout the life span of
the species.
c. Type III survivorship curve: Mortality is greatest early in the life span of the
species.
4. Life history is divided into three phases: birth, reproduction, and death;
population size is a function of:
a. Age of first reproduction.
b. Clutch size.
c. Number of reproductive events.
d. Biological fitness.
D. Population growth.
1. Continuous population growth without environmental limitations produces an
exponential growth curve.
2. Initial population growth rate is exponential until population size reaches a level
at which the environment cannot support additional growth and the population
size becomes relatively constant.
3. Recruitment.
4. Carrying capacity.
5. Population regulation.
a. Density-independent limiting factors.
b. Density-dependent limiting factors.
c. r-strategists.
d. k-strategists.
Communities
A. Niche.
1. Fundamental niche.
2. Realized niche.
3. Connell’s barnacles.
B. Biological interactions.
1. Competition.
a. Interspecific competition.
b. Intraspecific competition.
c. Competitive exclusion.
d. Resource partitioning.
C. Predator-prey relationships.
1. Herbivore.
2. Carnivore.
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3. Keystone species.
D. Symbiosis.
1. Mutualism.
2. Commensalism.
3. Parasitism.
V. Ecosystems: Basic Units of the Biosphere
A. Energy flows through an ecosystem.
1. Producers/autotrophs.
2. Photosynthesis.
3. Primary productivity.
4. Consumers.
5. Heterotroph.
6. First-order (primary) consumers.
7. Second-order (secondary) consumers.
8. Third-order (tertiary) consumers.
9. Omnivores.
10. Detritivores.
11. Food chain and web.
12. Dissolved organic matter (DOM).
13. Trophic level.
a. 10% rule.
14. Trophic pyramids.
a. Pyramid of energy.
b. Pyramid of biomass.
c. Pyramid of numbers.
B. Biogeochemical cycles: cycling of nutrients through trophic structures.
1. Hydrological cycle (water cycle).
2. Carbon cycle.
3. Nitrogen cycle.
VI. The Biosphere
A. Distribution of marine communities in the biosphere (refer to Figure 2-24).
B. Pelagic division.
1. Neritic zone.
2. Oceanic zone.
3. Photic zone.
4. Disphotic zone.
5. Aphotic zone.
6. Plankton.
7. Nekton.
8. Neuston.
C. Benthic division.
1. Intertidal zone.
2. Bathyal zone.
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3.
4.
5.
6.
Abyssal zone.
Hadal zone.
Epifauna.
Infauna.
Suggestions for Presenting the Material
1. This chapter is about interactions of organisms with one another and their
environment. Try handing out a list of challenge questions, such as a list of the
adaptations necessary to survive in the intertidal zone or challenges to life in the
photic zone, and let students brainstorm using the think-pair-share strategy for
about 10 minutes. At the end of the 10 minutes, each group of students should
present their list. Use these student-generated points as a springboard for the lecture.
2. Video clips of species interactions from the Blue Planet and Planet Earth series
highlight more interesting adaptations to marine environments. Nothing captures
student interest as quickly as amazing underwater video sequences.
Classroom Discussion Ideas
1.
In what ways do humans disrupt the nitrogen cycle? What are the impacts of these
disruptions?
2. How are the concepts of carrying capacity and competition related?
3. After looking at the food pyramid, what inferences can be made about the
population sizes of top consumers as opposed to primary producers?
Videos, Animations, and Websites
Videos
Ocean Adventures with Cousteau. (DVD, PBS, 2006)
This series of five videos covers a range of habitats and animals.
http://www.pbs.org/kqed/oceanadventures/series/
The Blue Planet.
Well known for its stunning photography, this series also helps showcase the wide
range of aquatic habitats.
http://dsc.discovery.com/tv/blue-planet/blue-planet.html
Planet Earth.
The epitome of natural history documentaries, the episodes “Shallow Seas” and “Ocean
Deep” both cover marine life exclusively.
http://dsc.discovery.com/tv/planet-earth/
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http://dsc.discovery.com/videos/planet-earth-deep-oceans/
http://dsc.discovery.com/convergence/planet-earth/guide/seas.html
Animations
The Hydrologic Cycle.
This animation details the hydrologic cycle.
http://polaris.umuc.edu/cvu/envm/hydro/hydrologic-flash.html
Nitrogen Cycle.
This animation details the nitrogen cycle.
http://uccpbank.k12hsn.org/courses/APEnvironmentalScience/course%20files/multimedi
a/lesson09/animations/2b_nitrogen_cycle.html
The Carbon Cycle.
This animation details the carbon cycle.
http://uccpbank.k12hsn.org/courses/APEnvironmentalScience/course%20files/multimedi
a/lesson08/animations/2b_carbon_cycle.html
Websites
EPA Marine Ecosystems.
An introduction to marine ecosystems with links to other sites.
http://www.epa.gov/bioiweb1/aquatic/marine.html
University of California Museum of Paleontology.
An introduction to the major marine biomes.
http://www.ucmp.berkeley.edu/exhibits/biomes/marine.php
United Nations Atlas of the Oceans.
An overview of the physical and chemical properties of the ocean.
http://www.oceansatlas.org/unatlas/about/physicalandchemicalproperties/background/s
eemore2.html
United Nations Atlas of the Oceans.
An overview of the ecology of the ocean.
http://www.oceansatlas.org/servlet/CDSServlet?status=ND0xODkzJjY9ZW4mMzM9KiY
zNz1rb3M~
Chapter 2
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Suggested Answers to End of Chapter Questions
Multiple Choice
1. e. higher salinity, coarse sediments, and smaller food
2. a. mutualism
3. d. 1,000 kilograms
4. b. the sun
5. c. phytoplankton
6. c. a type III curve
7. c. 250 tuna
8. b. uniform
9. c. How many of its offspring survive to produce offspring?
Matching
1. b.
2. d.
3. a.
4. e.
5. c.
6. c.
7. e.
8. a.
9. b.
10. d.
11. c.
12. e.
13. b.
14. d.
15. a.
Short Answer
1. What are six abiotic factors that affect the distribution of organisms in an ecosystem?
The abiotic factors that affect the distribution of marine organisms in an ecosystem
are: sunlight, temperature, salinity, pressure, nutrients, and wastes.
2. What would probably happen to the natural balance in a community if the population
of predators dramatically decreased or was wiped out?
If the population of predators dramatically decreased or disappeared, the
population of prey would explode until the resources supporting the prey
population were depleted.
3. What is the difference between a community and an ecosystem?
The community is a group of organisms of differing species living together in a
habitat. An ecosystem is the biological community and the abiotic factors (physical
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Fundamentals of Ecology
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and chemical parameters), such a temperature and salinity.
4. Describe the three main types of symbiotic relationships found in nature.
The three types of symbiotic relationships that occur in nature are mutualism,
commensalism, and parasitism. In mutualism, both species benefit from the
symbiotic relationship. Commensalistic relationships have one species that benefits
from the symbiotic relationship while the other species is unaffected. In parasitism,
one species (the host) is harmed while the other species (the parasite) benefits.
5. Describe the marine nitrogen cycle.
Nitrogen enters the marine environment in one of two ways, as terrestrial run-off
and as nitrogen gas dissolving from the atmosphere. Nitrogen-fixing bacteria
convert nitrogen gas to ammonia, and other bacteria convert ammonia to nitrites
and nitrates. Nitrates are the form in which nitrogen is used by phytoplankton for
growth. Nitrogen enters the food chain and moves from one trophic level to the
next. When organisms die, nitrogen is released back into the marine environment.
6. Why are there fewer marine organisms in the ocean’s depths?
There are fewer organisms in the deep ocean because the biomass of the deep
ocean is limited by food supply. All food (organic matter) must fall from the photic
zone into the deep ocean.
7. Why are so many marine organisms ectotherms?
Since water has a high heat capacity, the temperature of the surface ocean varies
far less than that of the atmosphere. Further, below the photic zone and the
thermocline, the ocean temperature is constant. Since the temperature of the ocean
varies very little in the majority of the ocean, most organisms are adapted to the
environmental temperature of the ecosystem in which they evolved.
8. Why is energy transfer between trophic levels inefficient?
Trophic transfer of energy is inefficient because the majority of caloric intake
(energy) is expended in doing the work of life: foraging for food, hiding from
predators, metabolizing food, etc. Therefore, a very small amount of the energy is
incorporated into the organism’s biomass and available to the next trophic level.
9. How can groups of similar species avoid competition?
Groups of similar species can avoid competition by resource partitioning—this
partitioning can be physical (e.g., using a different part of the intertidal zone) or
temporal (e.g., feeding at night instead of during the day).
10. How can primary production be measured?
Primary production is estimated using the light and dark bottle method, and
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19
estimating carbon fixation is done by measuring dissolved oxygen. Since oxygen is
an end-product of photosynthesis, dissolved oxygen concentrations can be used to
estimate photosynthetic rate. The dark bottle is used to estimate the amount of
organic carbon lost to cellular respiration as a function of dissolved oxygen used,
and the light bottle estimates the net amount of organic carbon fixed
(photosynthesis minus respiration) as estimated by an increase in dissolved
oxygen concentration. By adding the organic carbon estimates of the light and dark
bottles together, the total (gross) amount of primary production can be estimated.
11. Why can’t most populations continually grow at an exponential rate?
Populations will exhibit exponential growth rates only when resources are
unlimited. This rarely occurs in nature.
12. Describe a detritus-based food chain.
Detritus is dead, decaying organic matter. In the majority of deep ocean
ecosystems, detritus from the ocean surface that falls into the deep ocean forms the
base of the food chain. In the absence of sunlight, all organic matter must come
from either eating live organisms (predation) or consuming detritus.
13. Describe two methods that could be used to determine the size of a population in the
wild.
Population size can be estimated in one of two ways. The first method is to divide
the habitat into smaller subdivisions or plots and count all the organisms in a
subset of plots. Multiply the average of the number of individuals per plot by the
total number of plots to estimate population size. A second method is called mark
and recapture. In this method of estimating population size, an initial sample is
taken and all organisms in the sample are marked or tagged in some way so they
can be identified later. A second sample is taken at a later time, and the number of
marked (tagged) individuals is counted. The portion of marked individuals in the
second sample is used to estimate the total population size. The accuracy of
population size estimates increases as the number of samples used to estimate
population size increases.
14. What characteristics do you associate with an opportunistic species?
Opportunistic species tend to have relatively short life spans, reproduce early in
the life cycle, produce large numbers of offspring, and do not invest energy in
parental care of offspring.
15. What is the difference between an organism’s fundamental niche and its realized
niche?
The fundamental niche is the broadest definition of the species niche, the resources
and habitats it could potentially utilize. The realized niche is what the organism
20
Fundamentals of Ecology
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actually uses given the available resources and the other species in the habitat.
Thinking Critically
1. Does the area of overlap in Figure 2-12 indicate that species A and species B have
overlapping niches and will be in direct competition under those conditions? Why or
why not?
Figure 2-12 does indicate that species A and species B will be in direct competition
at intermediate salinities, smaller sediment particle sizes, and intermediate food
size (some of the overlap is green in color).
2. Why does it make good ecological sense for whales to feed on plankton?
Because only 10 percent of the total energy available at one trophic level is
available at the next trophic level; by consuming either primary producers or
primary consumers, the great whales are eating low on the food chain and
garnering far more energy for their feeding effort when compared to top-end
predators (such as the toothed whales).
3. Although the open ocean receives plenty of radiant energy and has a larger area, it is
not nearly as productive as the shallow coastal seas. Why?
Open ocean productivity is nutrient-limited; limiting nutrients such as nitrogen
and phosphorus are more plentiful in coastal seas because of terrestrial run-off and
coastal upwelling of cold nutrient-rich water. The only portions of the open ocean
that are productive are upwelling zones, because of higher concentrations of
limiting nutrients.
4. Why do organisms that live in tide pools have to be more tolerant of changes in
salinity than organisms that live in the open sea?
Organisms that live in tidal pools must be tolerant of changing salinities because
the increased evaporation in tidal pools at low tide increases salinity. When the
tide goes out and a fixed volume of seawater remains, water is lost to evaporation
during the day until the tide rises and floods the tidal pool. Wide fluctuations in
salinity, water temperature, and dissolved oxygen levels mean that organisms
inhabiting tidal pools have to be far more tolerant of environmental fluctuations
than open-ocean species.
5. Which type of competition do you think would be more intense, interspecific or
intraspecific? Why?
Intraspecific competition (competition between two or more organisms of the same
species) would be more intense because organisms of the same species would have
identical niches and would utilize the same resources in the same way.
Chapter 2
21
6. Would it be possible to have a pyramid of numbers where the trophic level above is
larger than the trophic level below? Explain using an example with marine
organisms.
Examination of Figure 2-18 would suggest that there are fewer great whales than
benthic organisms, yet benthic organisms feed on whale carcasses when they fall to
the ocean bottom and decompose. This would be one example of an ecosystem in
which a pyramid of numbers would be smaller for the trophic level in which the
whales belong as compared to the next trophic level of benthic detritivores (larger
numbers of smaller organisms).
7. Under what conditions would it be advantageous for a female to delay reproduction
until later in life?
All things being equal, larger females produce either more eggs (which equals
more offspring) or larger offspring that are more likely to survive and reproduce.
Delaying reproduction means that the female will be larger when it reproduces.
Suggested InfoTrac® Articles
“In Ocean's Teeming Top Layer, Scientists Find a Microbe Haven.” (Science
Desk.) Zimmer, C. The New York Times, (July 28, 2009).
“Marine Ecoregions of the World: a Bioregionalization of Coastal and Shelf
Areas.” (Marine Biogeography.) Spalding, M.D., H.E. Fo,; G.R. Allen, N. Davidson, Z.A.
Ferdana, M. Finlayson, B.S. Halpern, M.A. Jorge, A. Lombana, S.A. Lourie, K.D. Martin,
E. McManus, J. Molnar, C.A. Recchia, and J. Robertson. BioScience, (July–August 2007).
“Whaling Endangers More than Whales.” (Meeting: American Association for the
Advancement of Science). Ferber, D. Science, (Feb 25, 2005).
“Study Finds Shark Overfishing May Lower Scallop Population.” (National
Desk) Fountain, H. The New York Times, (March 30, 2007).
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Fundamentals of Ecology