1. Dynamics of Ecosystems: Community Ecology
Chapter 45
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2. Realized Niche
A organism’s niche is the total of all ways it utilizes the resources of its environment.
Fundamental - Entire niche potentially available to an organism.
Realized - Actual niche utilized by an organism.
Habitat is the place where an organism lives.

3. Realized Niche
Interspecific competition - Occurs when different species attempt to utilize the same resource.
Interference - Individuals fighting over the same resource.
Exploitative - Individuals utilizing shared resources.
Competition and Niche Use in Barnacles

4. Principle of Competitive Exclusion
The Principle of competitive exclusion states that no two species utilizing the same niche can coexist indefinitely.
One will eventually eliminate the other.

5. Resource Partitioning
Resource Partitioning occurs when species living in the same area partition available resources to avoid direct competition.
Sympatric species are similar species that live in the same geographical area.
Tend to exhibit greater differences in morphology than allopatric species (species that live apart from each other).
Character Displacement

6. Character Displacement
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7. Detecting Interspecific Competition
Negative effects of one species on another do not automatically indicate competition.
Presence of one species may attract a predator that consumes both, causing one species to have a lower population size than the other.
Must always look at underlying ecological mechanisms.

8. Predation and Prey Populations
Predation occurs when one organism consumes another.
Provides strong selective pressure on prey populations.
Any physiologic characteristic or behavior that would decrease the probability of capture should be strongly favored.
Increased fitness
Includes camouflage

9. Plant Defenses Against Herbivores
Morphological
Thorns, spines, etc.
Chemical
Secondary Chemical Compounds
Evolutionary Response of Herbivores
Certain groups of herbivores are associated with each group of plants protected by a particular secondary compound.
Coevolution

10. Animal Defenses Against Predators
Some animals that feed on plants rich in secondary compounds receive an extra benefit.
Caterpillars that feed on members of the milkweed family.
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11. Animal Defenses Against Predators
Defensive Coloration
Aposematic Coloration (warning coloration)
Individuals advertise poisonous nature.
Cryptic Coloration
Camouflage (Blending coloration)
Chemical Defenses
Poisons and stings
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12. Mimicry Batesian Non-venomous snake resembles a venomous snake
Palatable insects resemble brightly colored, distasteful species.
Mullerian
Unrelated protected species resemble one another.
Predators learn more quickly.

13. Coevolution and Symbiosis
Coevolution involves long-term mutual evolutionary character adjustments of two or more species.
Predator-prey interactions
Symbiotic Relationships
Two or more kinds of organisms live together in permanent relationships.
Commensalism, Mutualism and Parasitism.

14. Commensalism
One species of symbiotic relationship benefits while the other is neither helped or hurt.
Tropical fish and sea anemones
No clear distinction between mutualism as it is difficult to determine if the second member of the relationship gains benefit.
Can easily grade into parasitism.

15. Mutualism Both species of relationship gain benefit.
Mutual cooperation
Ants and Acacias
Ant has a place to live, protects tree from harmful insects
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16. Parasitism Bird lice on feather
Parasite is much smaller than the host and gains benefit while inflecting some form of harm to the host. Do not kill immediately.
Ectoparasites
External parasites - Lice
Parasitoids - Lay eggs on living hosts.
Endoparasites
Internal parasites
Extreme specialization
Bird lice on feather

17. Birds lay their eggs in the nests of other species. Cowbirds
Parasitism
Brood Parasites
Birds lay their eggs in the nests of other species.
Cowbirds
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18. Interactions Among Ecological Processes
Predation Reduces Competition
Reduce numbers of competitive species.
Parasitism Can Counter Competition
Parasite may effect sympatric species and thus influence interspecific interactions.
Keystone Species
Species that have a particularly strong effect on community composition.
Top predators
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19. Interactions Among Ecological Processes
Indirect Effects
Presence of one species may affect a second species through interactions with a third species.
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20. Succession
Succession is the process of ecosystems changing from a simple to a more complex structure.
Primary Succession - Occurs in bare or open areas.
Eutrophication of oligotrophic lakes.
Secondary Succession - Occurs following a disturbance (fire, flood, etc)
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21. Succession
Climax Community - Eventual stable point of succession. Concept is now tempered by several realizations:
Climate is dynamic.
Succession is often slow.
Region’s vegetation is determined to an extent by human activities.

22. Succession
Succession occurs because species alter the habitat and available resources in ways that favor other species.
Key Concepts
Tolerance
Facilitation
Inhibition

23. The Role of Disturbance
Disturbances interrupt and potentially alter the succession of plant communities.
Intermediate Disturbance Theory
Communities experiencing moderate levels of disturbance will have greater species richness than communities experiencing either smaller or larger levels of disturbance.
Simultaneous successional stages.
Dominant competitors kept at bay.

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