1. Chapter 21
Community Ecology

2. Species Interactions
Communities contain populations that interact in many ways
There are five major types of interactions (symbioses): predation, parasitism, competition, mutualism, and commensalism

3. Predation A predator captures, kills, and consumes the prey
Predation determines where and how a species lives
Regulates population size

4. Predators and Natural Selection
Natural selection favors adaptations that improve the efficiency of predators (the better the hunter, the more food to survive)
Examples: predator adaptations such as coat color, sharp teeth or claws, able to find prey (sense of smell, accurate vision)

5. Prey and Natural Selection
The survival of prey animals depend on their ability to avoid being eaten
Examples: camouflage, poison, behavior, ability to hide, able to outrun predator

6. Mimicry A harmless species resembles a poisonous one
The mimic is protected since it is avoided

7. Mullerian Mimicry
When several dangerous/poisonous species have similar warning coloration
Example: the black and yellow striped pattern on bees and wasps

8. Batesian Mimicry
When a harmless species mimics the warning coloration of a dangerous species
Example: coral snakes and scarlet king snakes

9. Plant-Herbivore Interactions
Plants have evolved adaptations that protect them from being eaten by herbivores
examples: thorns, spines, stinging hairs, tough leaves, chemical defenses

10. Secondary Compounds
Some chemicals in plants are poisonous, irritating, or bad-tasting
Many plant chemicals are used for medicines
There are many medicinal cures in rainforest plants, but they are being destroyed due to habitat destruction!

11. Parasitism One individual is harmed while the other benefits
The parasite feeds on the host
Ectoparasites (external)
Endoparasites (internal)

12. Parasitism and Evolution
Parasitism has caused an evolution of a variety of host defenses
Natural selection favors adaptations that allow a parasite to exploit its host (very specialized bodies and lifestyles)

13. Competition
The use of the same limited resource by two or more species
Competitive exclusion: one species can be eliminated from a community because of competition

14. Competition in Paramecia
G.F. Gause studied competition between two species of paramecia in the lab

15. Character Displacement
Competitors may evolve niche differences or anatomical differences that lessen the competition
Example: Darwin’s finches

16. Resource Partitioning
When similar species coexist, each species uses only part of the available resources
Example: warblers forage in different types of trees

17. Mutualism A cooperative relationship in which both species benefit
example: pollination (pollinators are attracted to a food source and transfer pollen to other flowers while feeding)

18. Commensalism One species benefits while the other is not affected
Example: cattle egrets feed on insects that fly out of the grass when the Cape buffalo is walking

19. 21.2 Properties of Communities
Species richness: the number of species a community contains
Species diversity: relates the number of species to the relative abundance of each species

20. Patterns of Species Richness
Varies with latitude
The closer to the equator, the more species (greatest in tropical rainforests)
E.O. Wilson found more ant species in a single tree in Peru than there are in the entire British Isles

21. Tropical Rainforests Climate is more stable than a temperate area
Plants can photosynthesize year-round
Tropical rainforests have the highest biodiversity on Earth

22. The Species-Area Effect
Larger areas usually contain more species than smaller areas (more habitats)
Most often applied to islands
Reducing the size of a habitat reduces the number of species

23. Community Stability
Stability refers to a community’s resistance to change and is directly related to species richness
The more species, the more interactions and the better a habitat can withstand a disturbance

24. 21.3 Succession
A gradual process of change and replacement of the types of species in a community
Ecosystems are constantly changing

25. Primary Succession
Occurs on a surface where no ecosystem existed before
Example: rocks, volcanic islands, cliffs, sand dunes

26. Primary Succession Happens very slowly
Bare rock  lichens  moss  grasses  shrubs  trees
Example: Galapagos Islands

27. Secondary Succession Most common type of succession
Occurs on a surface where an ecosystem previously existed
Occurs after an ecosystem is disturbed by humans or by storms, floods, earthquakes, or volcanoes

28. Secondary Succession
Pioneer species- the first organisms to colonize any newly available area
Grasses and weeds  shrubs  shade intolerant trees  shade tolerant trees 
climax community
Example: eruption of Mt. St. Helens destroyed
44,460 acres of forest

29. Old-field Succession
When farmland is abandoned, it will start to turn back into a forest ecosystem
Pioneer plants such as grasses and weeds will start to grow
After about 100 years, the field will return to a climax community

30. Old-field Succession