Community Ecology
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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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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


Community concept
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



Diversity and composition models
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



Island biogeography
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



Community structure1
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)


Habitat and ecological niche
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



Competition between populations
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


Competition between two laboratory populations of paramecium
Competition BetweenTwo Laboratory Populations of Paramecium


Character displacement in finches on the gal pagos islands
Character Displacement in Fincheson the Galápagos Islands


Niche specialization among five species of coexisting warblers
Niche Specialization AmongFive Species of Coexisting Warblers


Competition between two species of barnacles
Competition BetweenTwo Species of Barnacles


Predator prey interactions
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


Predator prey interaction between paramecium caudatum and didinium nasutum
Predator-prey Interaction BetweenParamecium caudatum and Didinium nasutum


Predator prey interaction between a lynx and a snowshoe hare
Predator-prey InteractionBetween a Lynx and a Snowshoe Hare


Prey defenses
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




Mimicry
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


Mimicry among insects with yellow and black stripes
Mimicry Among Insects withYellow and Black Stripes


Symbiotic relationships
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



Commensalism
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


Clownfish among sea anemone s tentacles
Clownfish AmongSea Anemone’s Tentacles


Mutualism
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


Mutualism between the bullhorn acacia tree and ants
Mutualism Betweenthe Bullhorn Acacia Tree and Ants



Community development
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




Succession models
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


Succession models1
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


Community diversity
Community Diversity

  • Community stability can be recognized in three ways

    • Persistence through time

    • Resistance to change

    • Recovery once a disturbance has occurred


Intermediate disturbance hypothesis
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



Predation competition and biodiversity
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



Review
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



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