Topic 16 - Population Cycles Predation (BIOL 2300)

Lotka-Volterra models

foundation for understanding predator-prey population oscillations

• differential equations (dN/dt) express the rate of non-linear growth of both predator and prey populations:

P = predator population size

H = prey population size

underlying principle

population sizes of predators & prey are linked through density-dependent influences each species has on the other’s birth and death rates

• prey-death rates influenced by size of predator pop.s

• predator-birth rates influenced by size of prey pop

functional response

relationship between prey density and predator consumption rate

• predator consumption rate increases with prey density

• remember 3 types f functional responses (prey density ~ search & handling time)

p =

efficiency of predator to capture prey (predator efficiency)

numerical response

relationship between predator consumption rate and predator offspring production rate

• predators produces offspring at a higher rate as their consumption rate of prey increases

*as consumption rate increases, rate of offspring production also increases

a =

efficiency of the predator to convert the prey consumed into offspring

*this is different for each predator

L-V models: prey population (H) - equation has 2 components

1st: exponential growth model (unlimited growth)

2nd: mortality of prey pop inflicted by predator only

assumption of Lotka-Volterra model

predation varies in direct proportion to H & P

• as H and P increase -|> encounter rates of predators and prey increases (s decreases)

growth of prey population will ______ ______ as p, H and P increase

decline faster

co-evolution

predators act as a selective pressure on prey species and vice versa

• prey traits that reduce changes of being detected and captured by predators will increase fitness

• e.g. cryptic coloration, chemical defenses, protective armor, behavioral strategies

• natural selection will result in more evasive prey/ less able to capture

failure to capture prey results in reduced _____ of predators

fitness

• predator traits that increase the chances of capturing prey will increase fitness

• natural selection will result in more skilled predators

T/F: predator and prey populations are in an “arms race|

true

• predators and prey coevolve, with the prey one step ahead of the predators to avoid going extinct