1. Pedro Ribeiro de Andrade Gilberto Câmara
Predator-Prey Models
Pedro Ribeiro de Andrade
Gilberto Câmara

2. Acknowledgments and thanks
Many thanks to the following professors for making slides available on the internet that were reused by us
Abdessamad Tridane (ASU)
Gleen Ledder (Univ of Nebraska)
Roger Day (Illinois State University)

3. “nature red in tooth and claw”

4. One species uses another as a food resource: lynx and hare.

5. The Hudson’s Bay Company

6. hare and lynx populations (Canada)
Note regular periodicity, and lag by lynx population peaks just after hare peaks

7. Predator-prey systems
The principal cause of death among the prey is being eaten by a predator.
The birth and survival rates of the predators depend on their available food supply—namely, the prey.

8. Predator-prey systems
Two species encounter each other at a rate that is proportional to both populations

9. predator population decreases predator population increases
Predator-prey cycles
normal prey population
prey population
increases
prey population
increases
predator population decreases
as less food
predator population increases
as more food
prey population decreases
because of more predators

10. Generic Model f(x) prey growth term g(y) predator mortality term
h(x,y) predation term
e - prey into predator biomass conversion coefficient
MTBI summer 2008

11. Lotka-Volterra Model r - prey growth rate : Malthus law
m - predator mortality rate : natural mortality
a and b predation coefficients : b=ea
e prey into predator biomass conversion coefficient
MTBI summer 2008

12. Predator-prey population fluctuations in Lotka-Volterra model

13. Predator-prey systems
Suppose that populations of rabbits and wolves are described by the Lotka-Volterra equations with: k = 0.08, a = 0.001, r = 0.02, b =
The time t is measured in months.
There are 40 wolfes and 1000 rabbits

14. Phase plane
Variation of one species in relation to the other

15. Phase trajectories: solution curve
A phase trajectory is a path traced out by solutions (R, W) as time goes by.

16. Equilibrium point
The point (1000, 80) is inside all the solution curves. It corresponds to the equilibrium solution R = 1000, W = 80.

17. Hare-lynx data

18. Hare-lynx data