1. Chapter 46 Community Structure and Biodiversity

2. Impacts, Issues: Fire Ants in the Pants Argentine fire ants first entered the US in the 1930s, probably on cargo ships Fire ants are more dangerous and competitive than native ants Their invasion disturbs ground-nesting birds and animals that feed on native ants

3. Impacts, Issues: Fire Ants in the Pants Ecologists enlist the aid of two fly species that attack fire ants in their native habitat Another option is fungi or protists that infect fire ants but not native ants Knowledge of community structure is vital to understanding the effects of invading species

4. Forest of New Guinea Community includes nine species of pigeons that partition the food supply Pigeons disperse seeds of the trees that provide their food (fruit) These are just a few of the many interactions that shape this community

5. Community All the populations that live together in a habitat Type of habitat shapes a community’s structure

6. Factors Shaping Community Structure Climate and topography Available foods and resources Adaptations of species in community Species interactions Arrival and disappearance of species Physical disturbances

7. Niche Sum of activities and relationships in which a species engages to secure and use resources necessary for survival and reproduction

8. Realized & Fundamental Niches Fundamental niche ◦ Theoretical niche occupied in the absence of any competing species Realized niche ◦ Niche a species actually occupies Realized niche is some fraction of the fundamental niche

9. Species Interactions Most interactions are neutral; have no effect on either species Commensalism helps one species and has no effect on the other Mutualism helps both species

10. Species Interactions Interspecific competition has a negative effect on both species Predation and parasitism both benefit one species at a cost to another

11. Symbiosis Living together for at least some part of the life cycle Commensalism, mutualism, and parasitism are forms of symbiosis

12. Mutualism Both species benefit Some are obligatory; partners depend upon each other ◦ Yucca plants and yucca moth ◦ Mycorrhizal fungi and plants

13. Yucca and Yucca Moth Example of an obligatory mutualism Each species of yucca is pollinated only by one species of moth Moth larvae can grow only in that one species of yucca

14. Fig. 46-3a, p.823

15. Fig. 46-2b, p.822

16. Mycorrhizae Obligatory mutualism between fungus and plant root Fungus supplies mineral ions to root Root supplies sugars to fungus

17. Competition Interspecific - between species Intraspecific - between members of the same species Intraspecific competition is most intense

18. Interference Competition Least chipmunk is excluded from piñon pine habitat by the competitive behavior of yellow pine chipmunks Yellow Pine Chipmunk Least Chipmunk

19. Competitive Exclusion Principle When two species compete for identical resources, one will be more successful and will eventually eliminate the other

20. Resource Partitioning Apparent competitors may have slightly different niches May use resources in a different way or time Minimizes competition and allows coexistence Figure 47.8 Page 825

21. Fig. 46-8b, p.825 bristly foxtail Indian mallow smartweed

22. Predation Predators are animals that feed on other living organisms Predators are free-living; they do not take up residence on their prey

23. Coevolution Joint evolution of two or more species that exert selection pressure on each other as an outcome of close ecological interaction As snail shells have thickened, claws of snail-eating crabs have become more massive

24. Predator-Prey Models Type I model: Each individual predator will consume a constant number of prey individuals over time Type II model: Consumption of prey by each predator increases, but not as fast as increases in prey density Type III model: Predator response is lowest when prey density is lowest

25. Canadian Lynx and Snowshoe Hare Show cyclic oscillations Krebs studied populations for ten years Fencing plots delayed cyclic declines but didn’t eliminate them Aerial predators, plant abundance also involved Three-level model

26. Fig. 46-10b, p.827

27. Fig. 46-10a, p.827

28. Prey Defenses Camouflage Warning coloration Mimicry Moment-of-truth defenses

29. Predator Responses Any adaptation that protects prey may select for predators that can overcome that adaptation Prey adaptations include stealth, camouflage, and ways to avoid chemical repellents

30. Parasitism Parasites drain nutrients from their hosts and live on or in their bodies Natural selection favors parasites that do not kill their host too quickly

31. Ecological Succession Change in the composition of species over time Classical model describes a predictable sequence with a stable climax community

32. Types of Succession Primary succession - new environments Secondary succession - communities were destroyed or displaced

33. Pioneer Species Species that colonize barren habitats Lichens, small plants with brief life cycles Improve conditions for other species who then replace them

34. Climax Community Stable array of species that persists relatively unchanged over time Succession does not always move predictably toward a specific climax community; other stable communities may persist

35. Fig. 46-19d, p.832

36. Keystone Species A species that can dictate community structure Removal of a keystone species can cause drastic changes in a community; can increase or decrease diversity

37. Exotic Species Species that has left its home range and become established elsewhere Becomes part of its new community Can have beneficial, neutral, or harmful effects on a community

38. Distance Effect The farther an island is from a mainland, the fewer species Closer islands receive more immigrants Species that reach islands far from mainland are adapted for long-distance dispersal and can move on

39. Distance Effect

40. Area Effect Larger islands tend to support more species than smaller islands More habitats Bigger targets Larger populations decrease extinction risks

41. Fig. 46-26, p.839