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 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