Community Interactions

1. Community Interactions Chapter 29

2. 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

3. Community • All the populations that live together in a habitat • Habitat is the type of place where individuals of a species typically live • Type of habitat shapes a community’s structure

4. 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

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

6. 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

7. 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

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

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

10. Mutualism • Both species benefit • Many examples in nature • Some mutualisms are obligatory; partners depend upon each other

11. 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

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

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

14. Forms of Competition • Competitors may have equal access to a resource; compete to exploit resource more effectively • One competitor may be able to control access to a resource, to exclude others

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

16. Competitive Exclusion Expt Paramecium caudatum Paramecium aurelia

17. 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

18. Lubchenco Experiment Periwinkles promote or limit diversity in different habitats Tidepools Rocks exposed at high tide

19. Resource Partitioning • Apparent competitors may actually have slightly different niches • Species may use resources in a different way or time • Minimizes competition and allows coexistence

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

21. Coevolution • Natural selection promotes traits that help prey escape predation • It also promotes traits that make predators more successful at capturing prey

22. Predator-Prey Cycles • Predator and prey populations may show an apparent correspondence PREY POPULATION PREDATOR POPULATION

23. Variation in Cycles • An association in predator and prey abundance does not always indicate a cause and effect relationship • Variations in food supply and additional predators may also influence changes in prey abundance

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

25. 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

26. 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

27. Types of Parasites • Microparasites • Macroparasites • Social parasites • Parasitoids

28. Succession Change in the composition of species over time

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

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

31. 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

32. Cyclic Changes • Cyclic, nondirectional changes also shape community structure • Tree falls cause local patchiness in tropical forests • Fires periodically destroy underbrush in sequoia forests

33. Restoration Ecology • Natural restoration of a damaged community can take a very long time • Active restoration is an attempt to reestablish biodiversity in an area • Ecologists are actively working to restore reefs, grasslands, and wetlands

34. Community Instability • Disturbances can cause a community to change in ways that persist even if the change is reversed

35. Species Introductions • Introduction of a nonindigenous species can decimate a community • No natural enemies or controls • Can outcompete native species

36. 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

37. Endangered Species • A species that is extremely vulnerable to extinction • Close to 70 percent of endangered species have been negatively affected by exotic competitors

38. Nile Perch in East Africa • Nile perch were introduced into Lake Victoria as a food source • This predator ate native cichlids; drove many species to extinction • Now Nile perch species is close to crashing

39. Rabbits in Australia • Rabbits were introduced for food and hunting • Without predators, their numbers soared • Attempts at control using fences or viruses have thus far been unsuccessful

40. Kudzu in Georgia • Imported for erosion control • No natural herbivores, pathogens, or competitors • Grows over landscapes and cannot be dug up or burned out • May turn out to have some commercial use

41. Diversity by Latitude • Diversity of most groups is greatest in tropics; declines toward poles Ant diversity

42. Why Are Tropical Species Rich? • Resources are plentiful and reliable • Species diversity is self-reinforcing • Rates of speciation are highest in the tropics

43. 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

44. Distance Effect