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• Chapter 53 – Community Ecology
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What is a community?What is a community?
• A community is a group of populations of various species living close enough for potential interaction
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Community InteractionsCommunity Interactions
• Interspecific – interactions between different species within a community
• Competition
• Predation
• Herbivory
• Symbiosis
• Disease
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CompetitionCompetition
• Interspecific competition occurs when species compete for a resource that is in limited supply
• Competitive exclusion principle: one species will use the limiting resources more efficiently thereby eliminating the local competitor.
• Example: barnacle species in Scotland
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Competitive Exclusion Principle Competitive Exclusion Principle and the Concept of Nicheand the Concept of Niche
• Relates to concept of Niche: the sum total of the biotic and abiotic resources used by a species’
• Fundamental niche = potential• Realized niche = actual
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NicheNiche
• Two species cannot occupy the same niche = leads to competition
• Resource partitioning: altering ones niche to avoid competition; lizard example
• Character displacement: characteristics become more divergent; finch beak example
Resource Partitioning
Character Displacement
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PredationPredation
• Predator kills and eats prey; a +/- interaction• Predator mechanisms: acute senses, claws,
teeth, fangs, stingers, poison, speed, agility, coloration, and camouflage
• Defense mechanisms: alarm calls, maternal/paternal protection, mechanical defenses (spikes, spines, and hard shells), chemical defenses (toxins, poisons, and bad taste), coloration (aposematic coloration) and mimicry (Batesian and Mullerian).
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Coloration and MimicryColoration and Mimicry
Cryptic Coloration Aposematic Coloration
Batesian Mimicry
Mullerian Mimicry
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HerbivoryHerbivory
• Herbivory: a +/- interaction in which an herbivore eats parts of a plant or alga
• Predator mechanisms include specialized teeth or digestive systems, enhanced senses, and selective eating (leaving part of plant behind)
• Similar defense mechanisms as with predation, but chemical defenses and coloration are most common
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SymbiosisSymbiosis• Mutualism: an interaction that
benefits both species; a +/+ interaction, example = acacia trees and ants
• Commensalism: an interaction between species where one benefits while the other is neither harmed nor helped; a +/0 interaction, example = egrets and water buffalo
• Parasitism: a +/- interaction in which one organism (parasite) derives nourishment from another (host); pathogen = lethal
• Can you think of any additional examples (at least 1 of each)?
Mutualism
Commensalism
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MutualismMutualism
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Which forest is more diverse?Which forest is more diverse?
• Species diversity has 2 components:
• Species richness: total number of different species
• Relative abundance: proportion each species represents
• Answer = Ecologists would say community 1 has greater species diversity
Species Diversity
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Trophic StructureTrophic Structure
• Feeding relationships• Transfer of energy up
trophic levels– Primary producers– Primary consumers– Secondary consumers– Tertiary consumers– Quaternary consumers
• Food Chains, food webs
Trophic Levels
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Dominant and Keystone Dominant and Keystone SpeciesSpecies
• Dominant species: most abundant and have the most biomass, impact on a community can vary
• Keystone species: not abundant, but play critical role because of the niche they occupy within the community; examples include sea stars and sea otters
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Examples of Keystone SpeciesExamples of Keystone Species
Sea Star
Sea Otters
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DisturbanceDisturbance• An event that changes a community by
removing organisms and altering resources• Examples include a storm, fire, flood,
drought, overgrazing, or human activity• Can have long-term, positive effects
Prairie Disturbance Recovery
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SuccessionSuccession
• Transition in the species composition of a community overtime
• Primary succession: begins in a lifeless area with no soil, example – a new volcanic island
• Secondary succession: when an existing community has been cleared by some disturbance, leaves soil intact
Ecological Succession