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

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

Review – Consumer-Resource Interactions consumer-resource systems can have more than one stable state: consumer-imposed equilibrium resource-imposed equilibrium K

Facilitation commensalism, mutualism & symbiosis

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

Mutualism Obligate: one or both partners require mutualistic relationship for survival Facultative: species can live without their mutualistic partner

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

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

Refuge from physical stress: mussels, spartina, marsh elder and black rush

Facilitation – refuge from predation One species can protect another species from predators physical or chemical shelter (or both) camouflage

Facilitation – refuge from predation

Facilitation – refuge from competition One species can lessen the effects of competition for another species

Refuge from competition – Oculina and Mithrax

Facilitation – improved nutrient / energy availability One species can provide another species with improved access to energy or essential nutrients

Interaction Case Studies