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Review – Consumer-Resource Interactions Exploitative interactions (+,-) occur when a consumer species benefits at the expense of a resource species – e.g., herbivory, parasitism, predation Consumers can set limits on the distribution and abundance of resource populations Consumer-resource interactions produce cyclical growth and decline in population sizes of the interacting species: predator-prey cycles
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Review – Consumer-Resource Interactions predator-prey cycles generally stable, but environmental changes can act to change intensity, periodicity of cycles Lotka-Volterra model can reproduce predator prey cycles mathematically, but lacks some important aspects of the real process: time lag in predator-prey cycling due to time required to convert energy into actual offspring limits set on growth by carrying capacity limits set on predators by functional response
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Review – Consumer-Resource Interactions consumer-resource systems can have more than one stable state: consumer-imposed equilibrium resource-imposed equilibrium K
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Facilitation commensalism, mutualism & symbiosis
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Facilitation Interaction in which one or both parties benefits, and neither is negatively affected Commensalism (+,0): one individual benefits from interaction, the other is unaffected Mutualism (+,+): both individuals benefit from their interaction Symbiosis: a long-term, close mutualistic association between two organisms
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Mutualism Obligate: one or both partners require mutualistic relationship for survival Facultative: species can live without their mutualistic partner
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Facilitation The beneficial effects of facilitation can be realized in several different ways: reduced environmental stress reduced predation reduced competition increased access to resources transport / dispersal
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Facilitation – refuge from physical stress One species can provide another species with protection from a stressful environment nature of interaction can shift with time or changes in environment
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Refuge from physical stress: mussels, spartina, marsh elder and black rush
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Facilitation – refuge from predation One species can protect another species from predators physical or chemical shelter (or both) camouflage
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Facilitation – refuge from predation
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Facilitation – refuge from competition One species can lessen the effects of competition for another species
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Refuge from competition – Oculina and Mithrax
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Facilitation – improved nutrient / energy availability One species can provide another species with improved access to energy or essential nutrients
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Interaction Case Studies
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