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
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)
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