Population Cycles - Predation

do predators reduce prey populations below K?

yes, prey N is lower than K in the presence vs in the absence of predators

do predator prey interactions cause populations to oscilate?

ex. hudson bay company

• yearly data on number of lynx and hare furs exploited by trappers

• showed large, regular cycles every 10 yrs

• N of predator and prey species are highly synchronized - predator N trail prey N

lotka volterra models

foundation for understanding predator prey population oscillations

P

predator population size

H

prey population size

underlying principle of lotka volterra model

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

• prey - ____ rates influenced by size of predator pop

• predator - ____ rates influenced by size of prey pop

death, birth

what is it

effects of prey density on predator consumption rate

• functional response= relationship between prey density and predator consumption rate

• predator consumption rate increases with prey density

• p

p

efficiency of predator to capture prey (predator efficiency)

• (effects of prey density on predator consumption rates)

what is it

effects of prey density on predator population size

• numerical response

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

a

efficiency of the predator to convert the prey consumed into offspring

• (effects of prey density on predator population size)

numerical response

relationship between predator consumption rate and predator offspring production rate

LV model prey population equation has 2 components

1. exponential growth model (unlimited growth)

2. mortality of prey pop inflicted by predator only

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

grow faster

LV model assumes

predation varies in direct proportion to H and P

as H and P increase, encounter rates of predators and prey increase (s decreases)

LV predator population equation has 2 components

1. birth rate of predator

   • assume b of predators is +vely related to # of prey captured

   • # of prey captured =pHP

   • predators do not use 100% of energy consumed to produce offspring

   • predator pop will increase by apHP

2. mortality rate of predator

   • predators die at a constant rate = dP

   • independent of prey pop size

   • dependent on prey pop (intraspecific comp)

dH/dt=rH-pHP

prey pop

dP/dt=apHP-dP

predator pop

how do predator and prey pops oscillate

predator-prey interactions result in a stabilization of population growth for both pops

what is happening at dN/dt=0

r=0, b=d, stable equilibrium around which a population size is regulated

here instead of K, we assume that

• the prey population size (H) will be regulated around an equilibrium predator pop size (where dH/dt=0)

• the predator population size (P) will be regulated around an equilibrium prey pop size (where dP/dt=0)

explain this equation dH/dt=rH-pHp

prey population, rH=how prey pop increases, pHP=mortality rate

explain the equation dP/dt=apHP-dP

a=energy consumed that’s converted to predator offspring, p=efficiency of prey capture, dP=death rate of predators

what do predators acts as on prey species and vice versa

selective pressures

prey traits that reduce chances of being detected and captured by predators will increase what. and what are some examples

fitness. cryptic colouration, chemical defenses, protective armour, behavioural strategies (schooling, flocking)

natural selection will result in what for prey

smarter, more evasive prey

failure to capture prey results in what

reduced fitness of predators

natural selection will result in what for predators

smarter, more skilled predators

explain how predator and prey populations are in arms race

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

predators (can or cannot) reduce prey populations and predator prey interactions cause both populations to oscillate

can

______ models are an extension of the _____ equation and are the basis for understanding predator prey population oscillations

lotka volterra, logistic

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

density dependent

predator prey interactions act as selective pressures, resulting in the ________ of predator and prey species through natural selection

co evolution