-0+ - competitionamensalismpredation, parasitism 0 amensalismcommensalism + predation, parasitism...
Post on 19-Dec-2015
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- 0 +
- Competition
Amensalism Predation, parasitism
0 Amensalism
Commensalism
+ Predation, parasitism
Commensalism
Mutualism
Types of interactions
Consumer-Resource Interactions
• All life forms are both consumers and victims of consumers.
• Consumer-resource interactions organize biological communities into consumer chains (food chains):– consumers benefit at the expense of their
resources– populations are controlled from below by
resources and from above by consumers– The relative importance of top-down
versus bottom up control of populations is an important focus of ecological research
Some Definitions
• Predators catch individuals and consume them, removing them from the prey population.
• Parasites consume parts of a living prey organism, or host:– parasites may be external or internal– a parasite may negatively affect the
host but does not directly remove it from the population
More Definitions
Parasitoids consume the living tissues of their hosts, eventually killing them:– parasitoids combine traits of parasites and
predators
Herbivores eat whole plants or parts of plants:– may act as predators (eating whole plants) or as
parasites (eating parts of plants):•grazers eat grasses and herbaceous
vegetation•browsers eat woody vegetation
Theory: Lotka-Volterra Equations.
P = Predator population sizeV = Prey resource
dV/dt = rV – σPV
dV/dt = 0 P=r/σGeometric increase of prey (resource) in absence of predator; subtract predation, where σ is catching efficiency.
dP/dt = βVP – qP
dP/dt = 0 V=q/βGeometric decrease of predators in absence of prey;Predation loss of prey corrected for assimilation efficiency, or " β ".
Solution:Limit cycles (periodic solutions) such that
• Species can coexist, but• Random walk to extinction, • No interaction of prey with food supply
(& no time lags),• Predator mortality independent of prey density.
Cactoblastis chronology• 1839 Opuntia stricta in pot to Australia f/Texas or
Florida• 1900 10,000,000 acres• 1925 60,000,000 acres (i.e. area twice size NC)
increasing at 1,000,000 acres per year. Too dense to walk, 3-6' high. Sheep would not eat, horses could not traverse.
• Cactoblastis - northern Argentina2750 eggs in 1925; 2x106 eggs out in 19 locations
• 1930-31 Opuntia ravaged, mostly back to grass• 1932-33 Opuntia recovered some• 1935-40 Cactoblastis recovered and expanded• >1940 Only scattered Opuntia plants remained
L-V Assumptions
• Growth of victim population is limited only by predation (exponential growth)
• Predator is a specialist on victim (starves in absence of victims)
• Individual predators can consume an infinite number of victims
• Predator and victim encounter one other randomly in a homogeneous environment