Community Ecology

1. Community Ecology

2. Communities • A community is a group of organisms of different species that live in a particular area

3. Individualistic Hypothesis vs. Interactive Hypothesis • Individualistic Hypothesis: • A community is a chance group of species found in the same area because they have similar abiotic requirements • Interactive Hypothesis: • A community is a group of closely linked species locked together in mandatory biotic interactions that cause the community to function as an integrated unit

4. Interspecific Interactions • Interspecific interactions are interactions that occur between populations of different species living together in a community • There are 4 major interspecific interactions: • Predation (and parasitism) • Competition • Commensalism • Mutualism

5. Predation (and Parasitism) • (+ -) • The interaction is beneficial to one species and detrimental to the other • Predation: • When a predator eats its prey • Example in picture:

6. Predation (and Parasitism) • Parasitism: • Predators that live on or in their hosts, usually feeding off their body tissues or fluids • Usually do not kill their hosts • Examples:

7. Plant Defenses Against Herbivores • “Plants Fight Back!” • Plants have 2 major mechanisms by which they defend themselves against being eaten • Mechanical Defenses • Thorns, hooks, etc.

8. Plant Defenses Against Herbivores • Chemical Defenses • Produce chemicals that are distasteful or harmful to an herbivore • Morphine (opium poppy) • Nicotine (tobacco)

9. Animal Defenses Against Predators • Animals defend themselves against predators passively (hiding) or actively (fleeing) • Cryptic coloration (camouflage) makes prey difficult to spot • Aposematic coloration (warning coloration)warns predators not to each animals that may be toxic or may sting.

10. Animal Defenses Against Predation • Mimicry • When one species “imitates” or “mimics” another • Batesian mimicry • When one edible or harmless species mimics an bad-tasting (unpalatable) or harmful species • Example: hawkmoth mimics a snake

11. Animal Defenses Against Predation • Mimicry • Mullerian mimicry • Two species, both of which are unpalatable (taste bad) or harmful, resemble each other • Example: monarch butterfly (unpalatable) and queen butterfly (unpalatable) resemble each other

12. Symbiosis- close relationship between two organisms. • Parasitism (+,-) • Commensalism (+,neutral) • Mutualism (+,+)

13. Parasitism • One organism (the parasite) gets its nourishment from another organism (the host), which is harmed in the process • Endoparasites: • Live within host tissues (tapeworms) • Ectoparasites: • Feed on external surfaces (mosquitoes)

14. Interspecific Competition • Competition between organisms of different species • The Competitive Exclusion Principle: • Two species with similar needs for the same limiting resources cannot coexist in the same place • Niches may overlap but they may not be identical.

16. Ecological Niches • An organism’s niche is the specific role it plays in its environment • All of its uses of biotic and abiotic resources in its environment • Example: oak tree in a deciduous forest • Provides oxygen to plants, animals, etc. • Home for squirrels • Nesting ground for blue jays • Takes water out of the soil • Etc., etc.

17. Fundamental v. Realized Niche • Fundamental Niche includes resources an organism could theoretically use (if no competition) • Realized Niche includes resources it actually does use given competition from other species.

18. Resource Partitioning • Similar species develop ways to partition/divide resources in order to coexist.

19. Commensalism • (+0) relationship • One partner benefits, the other is not affected • Examples: • Cattle and cattle egret (birds) • Sea anemone and clownfish • Clownfish gets a place to live, sea anemone is not affected

20. Mutualism (++) relationship Both partners benefit from the relationship “You scratch my back, I’ll scratch yours” Examples: Ants & acacia tree tree provides high protein food in beltian bodies & habitat for nests inside thorns; ant protects against predators Mycorrhizae-fungal extentions on plant roots Plant gets increased water/nutrition, fungi gets food Hummingbirds & flowers Hummingbirds get food, flowers can reproduce

21. Dominant & Keystone Species • Dominant Species: • Species in a community that have the highest abundance or highest biomass • Sugar maple in eastern North America • Keystone Species: • Important to a community because of their ecological roles (niches), not by numbers • Sea otters control sea urchin population, which controls kelp population • Sea stars are keystone predators in many aquatic environments.

22. Ecological Succession • Ecological succession is a change in the species that live in a given area over a period of time • One community replaces another • Primary succession = occurs in places where soil is not yet formed (bare bedrock) • Secondary succession = occurs in places where there is soil, but where some disturbance has eliminated the previous community

23. Ecological Succession

24. Ecological Succession • The first organisms to inhabit an area undergoing succession are known as pioneer organisms • These are usually small organisms (bacteria, lichens, algae, etc.) • The ecosystem goes through a number of stages, with each new stage usually consisting of larger organisms than the last one • Once a community has become stable and is not changing much, it is known as a climax community

25. Causes of Ecological Succession • There are 3 major causes of ecological succession: • Human Activities - logging, mining, development, etc. • Natural Disasters/Disturbances - fires, volcanic eruptions, etc. 3. Natural Competition Among Species - Fictitious example: - turtles and frogs both eat crickets - frogs are faster, turtles are slower - frogs eat more crickets, turtles starve - turtle population dies out, frog population gets bigger