Lecture 15 Notes

Consumer-Resource Interactions: Predation, Herbivory, Parasitism

Predation: lethal
Herbivory: Eat while plants or parts of plants, usually non-lethal
Parasitism: Parasites consume parts of a living prey organism (host). May increase probability of death.
Parasitoids: consume hosts and cause its death; certain wasps and flies (wasps lay eggs in caterpillars)

Predators respond to prey abundance
Numerical response: more pray, predator population grows (lynx and hares)
Functional response: Predators eat more (Indiv. response)
Predator and prey can evolve in response to selection pressure of eating to survive and surviving to live another day.

Prey defenses:
chemical, fighting crypsis, escape, mimicry, aposematic, display of intimidation, dilution, mutualism, armor, acoustic, feigning death

Predation provides examples of adaptation by natural selection. Predator and prey can get involved in an arms race where each species evolves to increase mechanisms against the other.

Aposomatic coloration (warning): toxic prey offer bright colors or bold patterns to warn predators.
Mimicry: Prey not equipped with defenses resemble toxic prey. The toxic prey must outnumber defenseless prey or will lose its advantage.
- Batesian: model is toxic, mimic is not, requires learning by predator, destabilized by high abundance of mimics.
- Mullerian
Several unpalatable species adopt single pattern of warning coloration.
Likely to enhance learning among predators.

Predator-Prey Cycle:
Abundant prey is resource for predator so predator should increase in numbers
Once predators abundant, prey should decline
Predator will decline in absence of food supply
As long as some prey survive, numbers should increase

Lotka-Volterra Predator-prey model
dN/dt=rN-cNP (dN/dt zero at equilibrium) Prey
dP/dt=acNP-dp
Lotka volterra model follows type I functional response.
It exhibits neutral stability and structural instability.
There is a lag in the response of the predators to the prey and therefore the cycle is 1/4 cycle out of phase.
the oscillations increase in speed with increase in r - exponential growth rate of prey and d - death rate of predators.

Predator-Prey cycle:
The point where the equilibrium isoclines for predator and prey cross is the joint equilibrium point.
-In lab, predator and prey will cycle if prey are provided with a refuge.
- lynx and hare show cycling of pred. prey
- a spacial mosaic of habitats allows predator and prey to coexist and cycle.
- complexity of environment allows predators not to kill off prey
- prey evolve defenses
- other species offer alternative food source

When current food source or prey is limiting, a new species will be selected for primary food source.
- after escape from predation, prey population will rebound.

Keystone species concept:
- There are little players and big players. Keystone species that srongly affects the other species in the community. Removal of the keystone species can collapse structure of community.
ex: starfish and mussels

Predation causes large changes in the ecosystems because they affect a cascade or consumer-resource interaction. Invasive species are disastrous in the ability to become all consuming when they lack a predator to control their population.

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