ZOL 355 Study Guide - Midterm Guide: Snowy Owl, Switch, Arctic Fox
Prey Lecture 21: Predator Prey Interactions
I. Predation and periodicity
A. The population cycle of the lynx and hare: Charles Elton
1. About a 10 year cycle
B. Periodicity varies
1. Short Cycles
a) Predators feed on small herbivores
(1) arctic fox, snowy owl, rough-legged hawk (KNOW
EXAMPLES FOR EXAM)
b) small herbivores
(1) voles, lemmings (KNOW EXAMPLES FOR EXAM)
2. Long Cycles
a) Predators feeding on large herbivores
(1) red fox, lynx, goshawk, horned owl (KNOW EXAMPLES
FOR EXAM)
b) large herbivores
(1) hare, muskrat, ruffed grouse, ptarmigan (KNOW
EXAMPLES FOR EXAM)
II. Modeling Predator-prey interactions- Lotka-Volterra Model
What do we need to know for these guys?
Important questions regarding influences of predators
Do they reduce prey populations below K?
Do they cause oscillations?
III. Predator (Sharks) -prey (squid) interactions-Lotka-Volterra Model
A. exponential growth rate equation: dN/dt = rN
B. Growth rate of prey (squid) population is dR/dt
1. R = prey population
Growth rate = Exponential Growth - Removal of prey
Of Prey Pop Rate of Prey by predators
Exponential growth of prey = rR
Removal of prey by predators: cRP
c = capture efficiency
C. Comments on growth rate of prey (squid): dR/dt
dR/dt = rR - cRP
1. In absence of predators describe the growth rate of the prey population.
If P = 0 then dR/dt = exponential (It keeps growing)
dR/dt = rR - cRP
2. Predation varies in proportion to the chance that predators and prey come
in contact with one another (R*P)
3. What factors would cause the growth rate of the prey population to
increase?
a) Number of prey
b) Number of predators
c) Growth rate efficiency
d) Many more
D. Growth rate of predator population: dP/dt
Growth rate Birth Rate Death Rate
Of Predator = of predators - of predators
Population
Birth rate: acRP
a = assimilation efficiency
(ability to convert food into biomass)
c = Capture Efficiency
R = Prey Population Size
P = Predator Population Size
dP/dt = acRP – dP
Death term: dP (NEED TO KNOW EQUATION BUT NOT
GOING TO GET STORY PROBLEMS)
d = Per Capita death rate
P = Predator Population Size
E. What factors would cause the growth rate of predators to increase based on
dP/dt?
1. Assimilation efficiency (I think i missed something in the first one)
2. Increase capture efficiency
3. Increase prey population
4. Decrease the death term
dP/dt = acRP - dP
Document Summary
Predation and periodicity: the population cycle of the lynx and hare: charles elton, about a 10 year cycle, periodicity varies, short cycles, predators feed on small herbivores. Examples for exam) (1) arctic fox, snowy owl, rough-legged hawk (know: small herbivores (1) voles, lemmings (know examples for exam, long cycles, predators feeding on large herbivores (1) red fox, lynx, goshawk, horned owl (know examples. For exam) b) large herbivores (1) hare, muskrat, ruffed grouse, ptarmigan (know. Predator (sharks) -prey (squid) interactions- lotka-volterra model: exponential growth rate equation: dn/dt = rn, growth rate of prey (squid) population is dr/dt, r = prey population. Of prey pop rate of prey by predators. Removal of prey by predators: crp c = capture efficiency: comments on growth rate of prey (squid): dr/dt dr/dt = rr - crp. In absence of predators describe the growth rate of the prey population. Of predator = of predators - of predators.
