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Outline

Outline. The Concept of the Community Diversity and Composition Models The Structure of Communities Island Biogeography Habitat and Ecological Niche Competition Between Populations Predator-Prey Interactions Symbiotic Relationships Community Development Community Biodiversity.

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  1. Community Ecology

  2. Outline • The Concept of the Community • Diversity and Composition Models • The Structure of Communities • Island Biogeography • Habitat and Ecological Niche • Competition Between Populations • Predator-Prey Interactions • Symbiotic Relationships • Community Development • Community Biodiversity

  3. Community Concept • 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

  4. Community Structure

  5. Diversity and Composition Models • Gleason - Individualistic Model • Each population is there because its abiotic requirements are met • Clements - Interactive Model • Community is the highest level of organization • Dependent on biotic interactions

  6. Species Richness of Communities

  7. Island Biogeography • MacArthur and Wilson • Developed a general model of island biogeography • Explains and predicts how the community diversity of an island is affected by • Distance from the mainland, and • Size of the island

  8. Model of Island Biogeography

  9. Community Structure • Competition • When two species compete, the abundance of both species is negatively impacted • Predation (or parasitism) • Expected to increase the abundance of the predator (or parasite) • And reduce the abundance of the prey (or host)

  10. Habitat and Ecological Niche • Habitat • The area an organism lives and reproduces in • Ecological niche • The role a species plays in its community • Includes 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

  11. Feeding niches for Wading Birds

  12. Competition Between Populations • Interspecific competition • Members of different species require the same resource • The supply of the resource is limited • Competitive Exclusion Principle • No two species can occupy the same niche at the same time • Resource Partitioning decreases competition • Can lead to character displacement

  13. Competition BetweenTwo Laboratory Populations of Paramecium

  14. Character Displacement in Fincheson the Galápagos Islands

  15. Niche Specialization AmongFive Species of Coexisting Warblers

  16. Competition BetweenTwo Species of Barnacles

  17. Predator-Prey Interactions • Predation • One living organism, the predator, feeds on another, the prey • Predator is larger • Predator has lower reproductive rate • Prey usually entirely consumed • Presence of predators can decrease prey densities, and vice-versa

  18. Predator-prey Interaction BetweenParamecium caudatum and Didinium nasutum

  19. Predator-prey InteractionBetween a Lynx and a Snowshoe Hare

  20. Prey Defenses • Prey defenses • Mechanisms that thwart the possibility of being eaten by a predator • Spines • Tough Epidermis • Poisonous Chemicals • Camouflage • Bright Coloration • Flocking Behavior

  21. Camouflage in the Anglerfish

  22. Anti-predator Defenses

  23. Mimicry • Mimicry • One species resembles another species • Mimicked species possesses an overt antipredator defense • Batesian Mimicry - Mimic lacks defense of the organism it resembles • Müllerian Mimicry - Mimic shares same protective defense

  24. Mimicry Among Insects withYellow and Black Stripes

  25. Symbiotic Relationships • Symbiosis • Interactions in which there is a close relationship between members of two species • Parasitism • Parasite derives nourishment from a host, and may use host as habitat and mode of transmission • Endoparasites • Ectoparasites

  26. The Life Cycle of a Deer Tick

  27. Commensalism • Symbiosis, cont. • Commensalism • A symbiotic relationship in which one species benefits and the other is indifferent • Remoras and Sharks • Many supposed examples may turn out to be mutualism or parasitism • Inferred amount of harm or benefit two species do to one another is subject to investigator bias

  28. Clownfish AmongSea Anemone’s Tentacles

  29. Mutualism • Symbiosis, cont. • Mutualism • A symbiotic relationship in which both members of the association benefit • Need not be equally beneficial to both species • Cleaning Symbiosis • Often help each other obtain food or avoid predation • Bacteria in human intestinal tract

  30. Mutualism Betweenthe Bullhorn Acacia Tree and Ants

  31. Cleaning Symbiosis

  32. Community Development • Ecological Succession • A predictable pattern of change in species replacements 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

  33. Secondary Succession

  34. Secondary Successionin a Forest

  35. Succession Models • Facilitation Model • Each stage facilitates invasion and replacement by organisms of the next stage • Succession in a particular area will always lead to the same type of community • Climax Community

  36. Succession Models • Inhibition Model • Colonists remain 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

  37. Community Diversity • Community stability can be recognized in three ways • Persistence through time • Resistance to change • Recovery once a disturbance has occurred

  38. Intermediate Disturbance Hypothesis • If widespread disturbances occur frequently, diversity will be limited • If diversity is high, only moderate disturbances have been occurring with moderate frequency

  39. The Intermediate Disturbance Hypothesis

  40. Predation, Competition, and Biodiversity • Predation by a particular species may reduce competition and increases diversity • Such predators are referred to as keystone predators • Exotic species • May lead to unbridled competition • Resultant reduction in biodiversity

  41. Effect of a Keystone Species

  42. Review • The Concept of the Community • Diversity and Composition Models • The Structure of Communities • Island Biogeography • Habitat and Ecological Niche • Competition Between Populations • Predator-Prey Interactions • Symbiotic Relationships • Community Development • Community Biodiversity

  43. Community Ecology

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