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 Universe 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 which may also vary in size. • A habitat is the place where a population lives. • A population is a group of living organisms of the same kind living in the same place at the same time. • All of the populations interact and form a community.

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

14. 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 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 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. Predators and Prey Density • I represents abundant prey; II represents a leveling off as predators consume their fill; III shows prey levels dropping off and predator response slowing

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

25. Prey Defenses • Camouflage • Warning coloration • Mimicry

26. 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

27. 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

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

29. 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

30. 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

31. End for now! The exam will cover material to this point! 80% on material since the last exam 20% will include material from the beginning of the class - general principles which you should know

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

33. 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.

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

35. 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.

36. 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

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

38. 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…

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

40. 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

41. 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…

42. Kudzu in Georgia

43. 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

44. Caulerpa taxifolia

45. 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.

46. 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

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

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

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

50. Surtsey: Volcanic Island Primary succession