Community Ecology

1. Community Ecology

2. Community Characteristics • Interactions among species • Species diversity • Trophic structure

3. Species Diversity • Species richness • The total number of different species • Species abundance • The proportion each species represents of the total individuals in the community

4. Species Diversity

6. Species Diversity

7. Species Richness • Heterogeneous vs homogeneous distribution

9. Figure 48.3

10. Trophic Structure • Feeding relationships between organisms • Transfer of food energy through food web • Influences community dynamics • Producers vs Consumers • Primary energy source is sunlight • Conversion of this energy source through trophic structure • Energy conversion is inefficient • Energy enters system as sunlight “lost” as heat • Food chain vs food web • Illustrates trophic interactions

11. Trophic Structure • Producer • autotrophic • Converts sunlight energy into chemical energy • Sun to sugars • Consumer • Primary consumer • Trophic level that feeds on producers • herbivores • Secondary consumer • Trophic level that feeds primarily on primary consumers • Typically smaller carnivores • Tertiary consumer • Trophic level that feeds primarily on secondary consumers • Quaternary Consumer • Trophic level that feeds primarily on teriary consumers

12. Trophic Structure • Detritivores • In soil • Feed on detritus (dead material) • Soil scavengers • Earthworms, soil nematodes • Decomposers • Recycle nutrients • Fungus, bacteria

13. Food chain • Detritivore • Decomposers • Omnivores?

14. Food Web

15. Food Web • Linkage based on trophic levels • Species can occupy more than 1 trophic level • Diagram complex relationships

17. Limitations of food chain • 4-5 levels (9) • Energetic Hypothesis • Inefficiency of E transfer • 10 % rule • Dynamic stability hypothesis • Long chains lack stability • Magnification of fluctuations in variable environments

18. Figure 48.4

20. Pyramid of Net Production

21. Energetic Hypothesis

23. All species are not created equally….

25. Dominant species • Species found in highest abundance or biomass in a community • Biomass • The sum weight of all individuals in a population • Important in interspecific interactions • Influence abiotic factors • Exploit competitive advantage or predator avoidance • Ex Invasive species • Absence impacts environment • Ex chestnut blight (40% of canopy cover) • Impacted insect diversity (7 extinct out of 56) • Redundancy model of community structure • Other tree spp (resources) remained • Focus on biotic impact

26. Competitive Advantage

27. Invasive Species

28. Keystone Species • Not necessarily dominant species in a community • Occupy a critical niche occupation that controls the community structure • Pisaster vs Mytilus (keystone vs dominant) • Offset competitive advantage • 15-20 ---5 • Sea Otter • Dynamic stability hypothesis??

29. Dominant Species

33. Keystone Species

39. Foundation Species • ecosystem engineers • Influence environment by causing physical changes to the structure of the community • Use behavior or biomass

43. Community Stability • Ability to resist disturbance • Natural disturbances • Storm • Fire • Flood • Results in patterns of ecological succession • Unnatural • Human induced disturbance

44. Disturbance • Any event that that changes a community, removes organisms, alters resources • Stability • Ability of a community to recover from sisturbance • Natural disturbance • Unnatural disturbance

45. Natural disturbance

47. Natural Fire

48. Crown Fire

49. Ponderosa Pine Forest Recovery

50. Natural disturbance