1. Chapter 54 ~ Community Ecology

2. Community structure
Community = group of populations of different species living close enough to interact
Richness (number of different species) and Abundance (each species numbers in a community) determine the Species Diversity of a community

3. Interactions
Interspecific = interactions between populations of different species within a community
Intraspecific = interactions within the same species

4. Interactions
Competition = (-/-) interactions that occurs when individuals of different species compete for a resource that limits the growth and survival of each species

5. Competition
Competitive Exclusion Principle = 2 species with similar needs for the same limiting resources cannot coexist in the same place
Gause experiment

6. Competition evidence Resource partitioning Character displacement
sympatric (same location) species consume slightly different foods or use other resources in slightly different ways
Character displacement
sympatric species tend to diverge in those characteristics that overlap
Ex: 7 Anolis lizard species perching sites in the Dominican Republic
Ex: Darwin’s finch beak size on the Galapagos Islands

7. Niche
Ecological niche = the sum of an organism’s use of biotic and abiotic resources in its environment; its “ecological role”
Fundamental = the set of resources a population is theoretically capable of using under ideal conditions
Realized = the resources a population actually uses
Thus, 2 species cannot coexist in a community if their niches are identical
Ex: Barnacle sp. on the coast of Scotland

8. Interactions
Predation = (+/-) interaction between species in which one species, the predator, kills and eats the other, the prey
May involve a keystone species/predator

9. Predation defense Cryptic coloration - (camouflage)
Aposematic coloration - (warning)
Mimicry- superficial resemblance to another species

10. Mimicry
Batesian= palatable/ harmless species mimics an unpalatable/ harmful model
Mullerian= 2 or more unpalatable, aposematically colored species resemble each other

11. Interactions
Herbivory = (+/-) interaction in which an organism eats parts of a plant or algae.
Plants can’t run away to avoid being eaten, so they have adaptations that help: toxins, spines, thorns

12. Interactions Symbiotic Relationships
Parasitism = (+/-) interaction in which one organism, the parasite, derives it nourishment from another organism, its host, which is harmed in the process

13. Symbioitic Relationships
Mutualism = (+/+) interactions in which both species benefit
Commensalism

14. Symbioitic Relationships
Commensalism = (+/0) interaction between species that benefits one of the species but neither harms nor helps the other

15. Species Impact on Community Structure
Dominant species = highest amount of biomass (sum weight of all the members of a population) and most abundant
Keystone species = exert control on community structure; if removed, they have a large impact on food web and might even cause the collapse of the ecosystem
Effects on the ecosystem are disproportionate relative to their abundance
Examples: sea otter, dragonfly, gray wolf, elk, starfish

17. How the Wolves Changed Rivers Video

18. Species Impact on Community Structure
Species diversity – number of different species in a community and relative abundance of each
Trophic structure – feeding relationships of organisms
Food chains and webs

19. Evapotranspiration relates to the amount of water evaporation from soil and plants
What relationship can you conclude from this graph about the water availability in an area compared to species richness?

20. Species Impact on Community Structure
Invasive species = organisms (typically introduced by humans) that take hold outside their native range
May not face the natural predators and agents of disease that would otherwise hold their populations at check
Ex: Kudzu

21. Succession
Ecological succession = transition in species composition over ecological time
Process of predictable and sequential rebuilding of the ecosystem

22. Succession Primary = begun in lifeless area where soil is not present
Succession Video
Primary = begun in lifeless area where soil is not present
Ex: volcanic activity, retreating glacier, sand dune formation, forest on Stone Mountain
Secondary= an existing community has been cleared by some disturbance that leaves the soil intact
Forest fires, flooding

23. Succession Primary succession Secondary succession
Pioneer species – first organisms to inhabit a barren area
Ex: mosses and lichen
Climax community – final stable community
Secondary succession
Ex: fires in Yellowstone National Park in 1988

24. Blowout after a storm and dunes will be rebuilt

25. Biogeographic factors
Community diversity dependent on:
Latitude of community: plant and animal life generally more abundant in the tropics, becoming less so moving toward poles
Area of community: the larger the geographic area, the more species the community has
Islands – isolation and limited size contributes to community diversity
Rates of immigration and extinction influenced by size of island and distance from mainland