Community Ecology

1. Community Ecology Chapter 47 Mader: Biology 8th Ed.

2. Outline • Diversity and Composition Models • Island Biogeography • Habitat and Ecological Niche • Competition Between Populations • Predator-Prey Interactions • Symbiotic Relationships • Community Development • Community Diversity Mader: Biology 8th Ed.

3. Community Concept • A community is an assemblage of populations interacting with one another within the same environment. • Composition is a listing of various species in the community. • Diversity includes both species richness and species diversity. Mader: Biology 8th Ed.

4. Diversity and Composition Models • Gleason - Individualistic Model • Each population in community is there because its own particular abiotic requirements are met by a particular habitat. • Clements - Interactive Model • Community is the highest level of organization. • Dependent on biotic interactions. Mader: Biology 8th Ed.

5. Island Biogeography • MacArthur and Wilson developed a general model of island biogeography to explain and predict the effects of distance from the mainland and size of an island on community diversity. • Island size and distance from population source affects species diversity. Mader: Biology 8th Ed.

6. Model of Island Biogeography Mader: Biology 8th Ed.

7. Community Structure • Competition for limited resources between two species has a negative effect on the abundance of both species. • Predation and parasitism are expected to increase the abundance of the predator and parasite at the expense of the abundance of the prey and its host. Mader: Biology 8th Ed.

8. Habitat and Ecological Niche • Habitat is the area an organism lives and reproduces in. • Ecological niche is the role an organism plays in its community, including its habitat and its interactions with other organisms. • Fundamental niche - All conditions under which the organism can survive. • Realized niche - Set of conditions under which it exists in nature. Mader: Biology 8th Ed.

9. Feeding Niches for Wading Birds Mader: Biology 8th Ed.

10. Competition Between Populations • Interspecific competition occurs when members of different species try to utilize a resource in limited supply. • Competitive Exclusion Principle - No two species can occupy the same niche at the same time. • Resource Partitioning decreases competition. • Can lead to character displacement. Mader: Biology 8th Ed.

11. Competition Between Barnacle Species Mader: Biology 8th Ed.

12. Character Displacement in Galápagos Finches Mader: Biology 8th Ed.

13. Predator-Prey Interactions • Predation occurs when one living organism, the predator, feeds on another, the prey. • Presence of predators can decrease prey densities, and vice-versa. Mader: Biology 8th Ed.

14. Lynx-Snowshoe Hare Interactions Mader: Biology 8th Ed.

15. Prey Defenses • Prey defenses are mechanisms that thwart the possibility of being eaten by a predator. • Spines • Tough Epidermis • Poisonous Chemicals • Camouflage • Bright Coloration • Flocking Behavior Mader: Biology 8th Ed.

16. Camouflage in the Anglerfish Mader: Biology 8th Ed.

17. Mimicry • Mimicry occurs when one species resembles another that possesses an overt antipredator defense. • Batesian - Mimic lacks defense of the organism it resembles. • Müllerian - Mimic shares same protective defense. Mader: Biology 8th Ed.

18. Symbiotic Relationships • Symbiosis refers to interactions in which there is a close relationship between members of two populations. • Parasitism • Parasite derives nourishment from a host, and may use host as habitat and mode of transmission. • Endoparasites • Ectoparasites Mader: Biology 8th Ed.

19. Commensalism • Commensalism is a symbiotic relationship in which one species is benefited and the other is neither benefited nor harmed. • Remoras and Sharks • Many examples may turn out to be mutualism or parasitism. • Amount of harm or benefit two species do to one another is partially determined by the investigator. Mader: Biology 8th Ed.

20. Mutualism • Mutualism is a symbiotic relationship in which both members of the association benefit. • Often help organisms obtain food or avoid predation. • Bacteria in human intestinal tact. • Need not be equally beneficial to both species. • Cleaning Symbiosis Mader: Biology 8th Ed.

21. Mutualism Between Bullhorn Acacia and Ants Mader: Biology 8th Ed.

22. Cleaning Symbiosis Mader: Biology 8th Ed.

23. Community Development • Ecological Succession • A change involving a series of species replacements in a community following a disturbance. • Primary Succession occurs in areas where there is no soil formation. • Secondary Succession begins in areas where soil is present. • Pioneer Species Mader: Biology 8th Ed.

24. Secondary Succession in a Forest Mader: Biology 8th Ed.

25. Succession Models • Facilitation Model • Succession in a particular area will always lead to the same type of community. • Climax Community • Each stage facilitates invasion and replacement by organisms of the next stage. Mader: Biology 8th Ed.

26. Succession Models • Inhibition Model • Colonists hold onto their space and inhibit growth of other plants until the colonists are damaged or die. • Tolerance Model • Different types of plants can colonize an area at the same time. • Chance determine which seeds arrive first. Mader: Biology 8th Ed.

27. Community Diversity • Community stability can be recognized in three ways. • Persistence through time. • Resistance to change. • Recovery once a disturbance has occurred. Mader: Biology 8th Ed.

28. Intermediate Disturbance Hypothesis • Moderate amounts of disturbances at moderate frequency are required for a high degree of community diversity. • If widespread disturbances occur frequently, diversity will be limited. Mader: Biology 8th Ed.

29. Intermediate Disturbance Hypothesis Mader: Biology 8th Ed.

30. Predation, Competition, and Biodiversity • In certain communities, predation by a particular species reduces competition and increases diversity. • Predators that regulate competition and maintain community diversity are referred to as keystone predators. • Introduction of exotic species into a new area may lead to unbridled competition and resultant reduction in biodiversity. Mader: Biology 8th Ed.

31. Review • Diversity and Composition Models • Island Biogeography • Habitat and Ecological Niche • Competition Between Populations • Predator-Prey Interactions • Symbiotic Relationships • Community Development • Community Diversity Mader: Biology 8th Ed.

32. Mader: Biology 8th Ed.