1. Biology Sylvia S. Mader Michael Windelspecht
Chapter 45
Community and Ecosystem Ecology
Lecture Outline
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2. Outline 45.1 Ecology of Communities 45.2 Community Development
45.3 Dynamics of an Ecosystem 2

3. 45.1 Ecology of Communities
Community Structure
A community is an assemblage of populations interacting with one another within the same environment.
The species composition (also called species richness) of a community is a listing of various species in the community.
Species diversity includes both species richness and the abundance of different species.

4. Ecology of Communities
Habitat and Ecological Niche
Habitat
The area where an organism lives and reproduces
Ecological niche
The role a species plays in its community
Includes its habitat and its interactions with other organisms
Fundamental niche - All conditions under which the organism can survive
Realized niche - Set of conditions under which it exists in nature

5. Ecology of Communities
Competition Between Populations
Competition occurs when members of different species try to utilize a limited resource
When two species compete, the abundance of both species is negatively impacted

6. Competition Between Two Laboratory Populations of Paramecium
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P. aurelia grown
separately
Population Density
P. caudatum grown
separately
Population Density
Both species
grown together
Population Density
Time

7. Ecology of Communities
Competition Between Populations
Competitive Exclusion Principle
No two species can indefinitely occupy the same niche at the same time
Resource partitioning decreases competition between species
Resource partitioning leads to niche specialization and less niche overlap between species
Character Displacement
Characteristics tend to become more divergent when populations belong to the same community than when they are isolated
Competition and resource partitioning may lead to character displacement 7

8. Character Displacement in Finches on the Galápagos Islands
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Species coexist on Abingdon,
Bindloe, James, and Jervis Islands 50
Percent of Sample 30 10
small
medium
Beak Depth
large
G. fortis exists alone
on Daphne Island 50
Percent of Sample 30 10
small
medium
Beak Depth
large
G. fuliginosa exists alone
on Crossman Island 50
Percent of Sample 30 10
small
medium
Beak Depth
large
G. fuliginosa
G. fortis
G. magnirostris

9. Niche Specialization Among Five Species of Coexisting Warblers
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Cape May
warbler
Black-throated
green warbler
Bay-breasted
warbler
Blackburnian
warbler
Yellow-rumped
warbler

10. Competition Between Two Species of Barnacles
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high tide
Chthamalus
area of
competition
Balanus
low tide

11. Ecology of Communities
Predator-Prey Interactions
Predation
One living organism, the predator, feeds on another, the prey
Predator is larger
Predator has lower reproductive rate
Prey usually entirely consumed
Presence of predators can decrease prey densities, and vice-versa
Population density of the predator can be affected by the prevalence of the prey, and vice versa

12. Island Biogeography Pertains to Biodiversity
MacArthur and Wilson
Developed a general model of island biogeography
Explains and predicts how the community diversity of an island is affected by
Distance from the mainland, and
Size of the island
The model of island biogeography suggests that the larger the conserved area, the better the chance of preserving more species.

13. Predator-prey Interaction Between a Lynx and a Snowshoe Hare
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140
hare
lynx
120
100 80
Number (thousands) 60 40 20
1845
1855
1865
1875
1885
1895
1905
1915
1925
1935 b.
(a): © Creatas/Punch-Stock RF; (b): Data from D.A. MacLulich, Fluctuations in the Numbers of the Varying Hare (Lepus americanus), University of Toronto Press, Toronto, 1937, reprinted 1974

14. Ecology of Communities
Prey defenses
Mechanisms that thwart the possibility of being eaten by a predator
Heightened senses
Speed
Protective armor
Protective spines or thorns
Tails or appendages that break off
Poisonous chemicals
Camouflage
Warning coloration
Flocking behavior

15. Antipredator Defenses
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eye
false head
a. Camouflage
b. Warning colorization
c. Fright
a: © Gustav Verderber/Visuals Unlimited; b: © Zig Leszczynski/Animals Animals/Earth Scenes; c: © National Audubon Society/A. Cosmos Blank/Photo Researchers, Inc.

16. Ecology of Communities
Mimicry
One species resembles another species that possesses an overt antipredator defense
Batesian Mimicry - Mimic lacks defense of the organism it resembles
Müllerian Mimicry - Mimic shares a protective defense with other species

17. Mimicry Among Insects a. Flower fly b. Longhorn beetle c. Bumblebee
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a. Flower fly
b. Longhorn beetle
c. Bumblebee
d. Yellow jacket
a: © Edward S. Ross; b: © Edward S. Ross; c: © James H. Robinson/Photo Researchers, Inc.; d: © Edward S. Ross

18. Ecology of Communities
Symbiotic Relationships
Symbiosis
An association between species in which at least one of the species is dependent on the other

19. Ecology of Communities
Symbiotic Relationships (continued)
Parasitism
Parasite derives nourishment from a host, and may use host as habitat and mode of transmission
Small parasites tend to be endoparasites
Ex: heartworms
Larger parasites tend to be ectoparasites
Ex: leeches
Effect of parasites on the health of the host can range from slightly weakening them to killing them over time 19

20. Ecology of Communities
Symbiotic Relationships (continued)
Commensalism
A symbiotic relationship in which one species benefits and the other is neither benefited nor harmed
Clownfish living within tentacles of sea anemones
Many supposed examples may turn out to be mutualism or parasitism

21. Clownfish Among Sea Anemone’s Tentacles
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Dave B. Fleetham/Visuals Unlimited

22. Ecology of Communities
Symbiotic Relationships (continued)
Mutualism
A symbiotic relationship in which both members of the association benefit
Need not be equally beneficial to both species
Cleaning symbiosis
Often help each other obtain food or avoid predation
Bacteria in human intestinal tract

23. © Bill Wood/Bruce Coleman, Inc.
Cleaning Symbiosis
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© Bill Wood/Bruce Coleman, Inc.

24. 45.2 Community Development
Ecological Succession
A change involving a series of species replacements following a disturbance
Primary succession occurs in areas where there is no soil formation
Secondary succession begins in areas where soil is present
The first species to begin secondary succession are called pioneer species

25. Secondary Succession in a Forest
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grass
low shrub
high shrub
shrub-tree
low tree
high tree

26. Community Development
Models About Succession
Facilitation Model
Each stage facilitates invasion and replacement by organisms of the next stage
Succession in a particular area will always lead to the same type of community, a climax community

27. Community Development
Models About Succession
Inhibition Model
Colonists remain and inhibit growth of other plants until the colonists are damaged or die
Tolerance Model
Different types of plants can colonize an area at the same time
Chance determines which seeds arrive first

28. 45.3 Dynamics of an Ecosystem
In an ecosystem,
Populations interact among themselves
Populations interact with the physical environment
The abiotic components of an ecosystem are the nonliving components:
Atmosphere
Water
Soil 28

29. Dynamics of an Ecosystem
The biotic components of an ecosystem are living things that can be categorized according to their food source:
Autotrophs
Heterotrophs 29

30. Dynamics of an Ecosystem
Autotrophs
Require only energy and inorganic nutrients
Generate the food necessary for the ecosystem
Require only inorganic nutrients and an outside energy source to produce organic nutrients
Photoautotrophs
Land plants and algae
Chemoautotrophs
Some bacteria 30