1. The Nature of Communities and Ecosystems

2. Stability A stable community or ecosystem is one that has the ability to replace itself – exist in place for more than one generation

3. Components of Stability 2 major components: 1) resistance - the ability of a community or ecosystem to avoid disturbance - how most people think of stability 2) resilience - the speed with which a community or ecosystem returns to its former state following a disturbance that has displaced it from its initial condition

4. Ecosystems and Stability Grassland – South AfricaRainforest – Puerto Rico

5. Additional Components of Stability Local stability describes the tendency of a community to return to its original state following a small disturbance Global stability describes the tendency of a community to return to its original state following a large disturbance

6. Adaptive Capacity of an Ecosystem

8. Adaptive Capacity of an Ecosystem - Chesapeake Bay

9. Adaptive Capacity in 3D

10. Current Adaptive Capacity

11. From Local vs. Global Stability dynamically fragile - a community which is stable only within a narrow range of environmental conditions dynamically robust - a community which is stable within a wide range of environmental conditions

12. Complexity and Stability

15. Current understanding - no clear relation between complexity and stability 1) complex, fragile communities of relatively constant environments (the tropical rainforests) are more susceptible to outside, unnatural disturbances than are simpler, more robust communities which experience regular climatic fluctuations (most temperate communities) 2) In stable environments you would expect to find K selected species (high competitive ability, high survivorship, low reproductive output) and such species will resist disturbance 3) In unstable environments you would expect to find r selected species (low competitive ability, low survivorship, but high reproductive output) that have little resistance but high resilience

16. Why is the World Green? Boreal Forest Outlined in Green

17. Spiny Water Flea

18. Spiny Water Flea Invasion

19. Spiny Water Flea Current Distribution

20. Spiny Water Flea Food Web

21. Mary Power

23. Eel River with steelheadEel River without steelhead

24. Direct and Indirect Effects Direct effects - effect of 1 species on another resulting from physical interaction between the two – interference competition, inadvertant interference, mutualisms, parasitism, predator- prey Indirect effects - an effect of one species on another that is not caused by a physical interaction between the two - these can only happen when more than two species are present

25. Pisaster starfish

27. Pisaster and Mytilus californianus

28. Food web with Pisaster Yellow – predator; red – filter feeder; blue – grazer; green - algae

29. Mytilus californianus

30. Food web without Pisaster Yellow – predator; red – filter feeder; blue – grazer; green - algae

31. Strong vs. Weak Interactors 1) Non-interactors - species does not affect population of those species with which it interacts 2) weak interactors - species only influences those species with which it interacts directly - effects may be large 3) strong interactors - species that directly and indirectly effects other species - these species are the most important in the community or ecosystem because a change in their numbers may cause changes in the entire ecosystem – keystone species

33. Aerial view Of 1989 Yellowstone Fire

34. Disturbance and Succession

35. Disturbance Disturbance - any agent which causes complete or partial destruction of the community resulting in the creation of bare space Disturbance agents: both physical and biological processes may cause disturbances, though we usually focus on physical processes - Physical - fires, ice storms, floods, drought, high winds, landslides, large waves Biological - severe grazing, predation, disease, things that inadvertently kill organisms - digging and burrowing

36. Wind Damage – July 4, 1999 Derecho

37. Wildfire – Southern California October 22, 2007