-0+ - CompetitionAmensalismPredation, parasitism 0 AmensalismCommensalism + Predation, parasitism CommensalismMutualism 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

Predation

Theory: Lotka-Volterra Equations. P = Predator population size V = Prey resource dV/dt = rV – σPV dV/dt = 0  P=r/σ Geometric increase of prey (resource) in absence of predator; subtract predation, where σ is catching efficiency. dP/dt = βVP – qP dP/dt = 0  V=q/β Geometric 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.

Testing the theory -- Gause’s Paramecia

Testing the theory -- Huffaker’s oranges

Case studies – Opuntia and Cactoblastis

Cactoblastis chronology 1839 Opuntia stricta in pot to Australia f/Texas or Florida ,000,000 acres ,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 Argentina 2750 eggs in 1925; 2x10 6 eggs out in 19 locations Opuntia ravaged, mostly back to grass Opuntia recovered some Cactoblastis recovered and expanded >1940 Only scattered Opuntia plants remained

Klamath weed and Chrysolina quadrigemina

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

Carrying capacity

Functional response

Keystone predators – Piaster and Mytillus