Community Structure and Biodiversity

1. Community Structure and Biodiversity Chapter 40

2. Ecosystems • Ecosystems vary in size. • They can be as small as a puddle or as large as the Earth itself. • Any group of living and nonliving things interacting with each other can be considered as an ecosystem.

3. Within each ecosystem, there are habitats • These may also vary in size. • A habitat is the place where a population lives. - Turlock habitat • A population is a group of living organisms of the same kind living in the same place at the same time. Turlock humans • All the different populations interact and form a community. City of Turlock

4. The community of living things interacts with the non-living world around it to form the ecosystem. • The habitat must supply the needs of organisms, such as food, water, temperature, oxygen, and minerals. • If the population's needs are not met, it will move to a better habitat. • Two different populations can not occupy the same niche at the same time, however.

5. 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

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 - What??? • 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 • Many examples in nature • Some mutualisms are obligatory; partners depend upon each other

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

14. Example: 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

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

16. 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

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

18. Competitive Exclusion Expt.Protists - living together Paramecium caudatum Paramecium aurelia

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 areanimals 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. 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

23. Species Interactions • Canadian lynx (dashed lines) versus snowshoe hares (solid line)

24. Prey Defenses • Camouflage • Warning coloration • Mimicry

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. Biological Controls • Parasites and parasitoids are commercially raised and release in target areas as biological controls • An alternative to pesticides • Must be carefully managed to not upset natural balances

29. Study: Cowbirds • Brown-headed cowbirds evolved in the Great Plains region of the U.S., living as commensalists with bison • As they migrated along with the bison, the cowbirds learned to lay eggs in the nests of other birds • Cowbird hatchlings push the “host” bird eggs out of the nest • Today, cowbirds parasitize some 15 species of birds

30. End

31. Succession Change in the composition of different of species over time

32. Pioneer Species • Species that colonize barren habitats - first come, first served! • Lichens, small plants with brief life cycles • Improve conditions for other species who then replace them • lose out to better adapted species • who themselves lost out to even better adapted species.

33. Types of Succession • Primary succession - new environments • Secondary succession - communities were destroyed or displaced • Following hurricanes • After the tsunami

34. Climax Community Eventually we arrive at the 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 • Multiple outcomes.

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

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

37. 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…

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

39. Species Introductions • Introduction of a nonindigenous species can decimate a community • Just recently Hawaii has introduces Sea Stars to control sea weed • WHY? There are; • No natural enemies or controls • Can outcompete native species

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

41. Kudzu in Georgia

42. 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 for humans

43. Caulerpa taxifolia

44. Caulerpa taxifolia • Researchers developed a hybrid, sterile strain of this green alga - for fish tanks. • Somehow it was released into the wild, where it reproduces asexually - down the drain!!! • Thrives in varying conditions and emits a toxin that poisons invertebrates and fishes • Illegal to import the “aquarium” strain into the U.S.

45. 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

46. Biodiversity • The sum of all species occupying a specified area during a specified interval, past and present

47. Diversity by Latitude • Diversity of most groups is greatest in tropics; declines toward poles • a) ant species • b) breeding birds

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

49. Surtsey: Volcanic Island Primary succession

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