1. -0+ - CompetitionAmensalismPredation, parasitism 0 AmensalismCommensalism + Predation, parasitism CommensalismMutualism Types of interactions

2. 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

4. 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

5. 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

6. Predation

8. 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 ".

14. 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.

15. Testing the theory -- Gause’s Paramecia

17. Testing the theory -- Huffaker’s oranges

21. Case studies – Opuntia and Cactoblastis

22. 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 Argentina 2750 eggs in 1925; 2x10 6 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

24. Klamath weed and Chrysolina quadrigemina

25. 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

26. Carrying capacity

27. Functional response

34. Keystone predators – Piaster and Mytillus