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Chapter 47 Community Ecology Community Ecology 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 2 Community Ecology 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 3 Community Structure 4 Community Ecology 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 5 Species Richness of Communities 6 Community Ecology 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 7 Model of Island Biogeography 8 Community Ecology 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) 9 Community Ecology 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 Feeding niches for Wading Birds 11 Community Ecology 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 Competition Between 13 Two Laboratory Populations of Paramecium Character Displacement in Finches on the Galápagos Islands 14 Niche Specialization Among Five Species of Coexisting Warblers 15 Competition Between Two Species of Barnacles 16 Community Ecology 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 17 Predator-prey Interaction Between 18 Paramecium caudatum and Didinium nasutum Predator-prey Interaction Between a Lynx and a Snowshoe Hare 19 Community Ecology 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 20 Camouflage in the Anglerfish 21 Anti-predator Defenses 22 Community Ecology 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 Mimicry Among Insects with Yellow and Black Stripes 24 Community Ecology 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 The Life Cycle of a Deer Tick 26 Community Ecology 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 Clownfish Among Sea Anemone’s Tentacles 28 Community Ecology 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 Mutualism Between the Bullhorn Acacia Tree and Ants 30 Cleaning Symbiosis 31 Community Ecology 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 Secondary Succession 33 Secondary Succession in a Forest 34 Community Ecology 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 Community Ecology 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 Community Ecology Community Diversity Community stability can be recognized in three ways Persistence through time Resistance to change Recovery once a disturbance has occurred 37 Community Ecology 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 38 The Intermediate Disturbance Hypothesis 39 Community Ecology 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 40 Effect of a Keystone Species 41 Community Ecology 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 42 Ending Slide Chapter 47 Community Ecology