Download lecture.11 - Cal State LA

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