Community ecology examines the interactions between populations of different species living in the same area. Species compete for limited resources but can coexist through mechanisms like resource partitioning, where species differentiate their use of resources to reduce competition. Disturbances can alter communities, initiating primary or secondary succession as the community reestablishes itself over time. Keystone species play an outsized role in community structure and ecosystem function.

1. Community Ecology Chapter 54 Jeff Jewett American College of Sofia Version 1.0 May 20 th , 2010

2. Community A group of populations (each population is one species) living close enough together to interact

3. Interspecific Interactions Occur between individuals of DIFFERENT species Competition - /- Predation / Herbivory +/ - Symbiosis Parasitism +/- Commensalism +/0 Mutualism +/+

4. Interspecific Competition (- / - ) Russian Ecologist G.F. Gause 1934 (Image from: http://www.biologycorner.com/bio4/ecology/communities.html 2 or more different species competing for same resource (food, habitat, water, protection, etc.) Ecological Niche : “sum of a species use of the biotic and abiotic resources in its environment” Habitat = “address,” niche = “profession” Competitive Exclusion Virtual Lab

5. Competitive Exclusion Principle 2 species cannot occupy the same niche in same community at the same time One will win, the other will die, migrate, or adapt C.E.P. leads to Resource Partitioning

6. Resource Partitioning “Peace treaties”

7. Interspecific Competition, Continued Resource Partitioning – differentiation of niches to allow similar species to coexist in a community (space, behavior, temporal) Fundamental niche – the niche a species could theoretically occupy, without competitors Realized niche – the niche a species actually occupies, with competitors

8. http://terrystuff.wordpress.com/2008/03/19/keratoses-barnacles-young-pretty-doctors/

11. Body changes as a result of resource partitioning Character Displacement

12. Galapagos Finches http://www.galapagoscruises.be/darwins-finches.jpg These birds show character displacement due to resource partitioning.

13. Predation Includes herbivory plants have defense chemicals, spines, thorns Predators: binocular vision, prey: monocular vision Camouflage Mimicry Warning (“aposematic”) coloration Predator-Prey Animation (NortonBooks) http://www.biologycorner.com/bio4/ecology/communities.html DANGER!

14. Photo: Dr. Shannon Savage, 2007 Count the toads….

15. http://www.alaska-in-pictures.com/data/media/4/bald-eagle-face_850.jpg http://commons.wikimedia.org/wiki/File:Muso_di_cavallo_%28horse_head%29.jpg Predator? Prey? Look at the eyes! (Well, and that beak…)

16. Symbiosis “ living together” Parasitism (+/-) Commensalism (+/o) – rare Mutualism (+/+) win-win! (Lichen, Coral, digestive bacteria, mycorrhizae on plant roots) http://www.saburchill.com/ans02/chapters/chap010.html лишей http://www.nearctica.com/ecology/pops/mutual.htm#coral

17. Commensal Interactions (+/0) Epiphytes (?) Whales/barnacles (?) Clownfish/Anemone (?) http://tolweb.org/treehouses/?treehouse_id=3390

18. 54.2 Species Diversity What makes a healthy ecosystem? Species richness (# species) Relative abundance (proportion)

19. Food Webs

20. Species with a large impact Dominant Species – most abundant, or most biomass Keystone Species – important niches (pollinators, top predators) Ecosystem Engineers – change the environment (humans, beavers, elephants)

21. Keystone Species – Seastars ( Pisaster ochraceus )

22. Keystone Species – Sea Otter

23. Regulates snowmelt runoff Reduces soil erosion Facilitates other plant growth FOOD! – squirrels, birds, bears Pinus Albicaulis : Subalpine keystone species

24. 54.3 Disturbance & Succession Disturbance – an event that changes a community by removing organisms or altering resource availability Fire, storm, human activity, drought, overgrazing, flood

25. Disturbance & Succession Primary Succession Secondary Succession (ACS Campus) Climax Community Non-equilibrium model (everything’s always changing!) Intermediate disturbance hypothesis

26. Primary Succession Mosses and lichens create soils in this example of primary succession from Yosemite National Park, CA. The valley emerged ~10,000 years ago after being scraped clean by a glacier Grasses, shrubs and even trees appear where soil has slowly developed.

27. The steep hillsides show early stages of primary succession (little or no soil), but the low, flat places accumulate soil and support grasses/trees. (Yosemite National Park, CA.)

28. Secondary Succession Yosemite National Park, CA . After a wildfire, grasses and tree seedlings grow up to replace the burned forest.

29. Secondary Succession Yosemite National Park, CA . Later after a wildfire, shrubs and short trees grow up to replace the burned forest. A few gray snags of the old burned forest are still visible.

30. Pond Succession http://www.biog1105-1106.org/demos/106/unit10/media/pondsucc.jpg

31. Biogeography & Community Diversity Hot & wet = more species (rainforests!) Equatorial regions – more than polar or temperate (older, friendlier climate) Larger area – support a higher number of species