HERBIVORY
Why is the world green?
1. Self-regulation by herbivores
2. Predation controls herbivore abundance
3. Plants have defenses against herbivores
a. mechanical
b. masting
c. mutualisms
d. chemical defenses – quantitative, qualitative
e. defense associations
4. Herbivory can stimulate plant productivity
5. Herbivory can stimulate diversity
PREDATION
Five tenets of predation:
1. predators have adaptations for exploiting prey
2. prey have adaptations for escaping predators
3. predators can control prey populations size
4. predator and prey populations often increase and decrease in regular cycles
5. predators exhibit three types of functional responses to prey density
I.
Adaptations for exploiting prey
a. morphological
b. behavioral
II.
adaptations for escaping predators
a. avoidance
b. crypsis
c. chemical defenses
i. aposematism
1. batesian mimicry
2. mullerian mimicry
III.
predator controls on prey population size
-over- and under-exploitation
IV.
predator and prey population cycles
a. habitat heterogeneity allows coexistence
b. oscillations modeled by Lotka-Volterra
i. terms
P=predator N
R=prey N
C=capture efficiency
r=intrinsic growth rate
a=efficiency of prey conversion to predator growth
d=death rate of predator
ii. predicting prey response to predators
- dR/dt = rR – cRP
iii. predicting predator response to prey
-dP/dt = acRP – dP
iv. joint equilibrium
-equilibrium isoclines
V. Functional responses of predator to prey
1. predators consume constant proportion of prey regardless of prey density
2. predation rate decreases as predators become satiated
3. predators are depressed at low prey density because prey are hard to find
 oscillations in predator-prey models reduced by:
1. predator inefficiency
2. density dependent limitation
3. alternative food for predator
4. refuges from predation
5. time lags in response
 multiple steady state models