Chapter 15: Predation and Herbivory

what is the direct effect of predators on prey population

abundance

what is the indirect effect of prey predators on prey population

dynamics and evolution

what can prey populations influences

predator population dynamics and evolution

what is an example predators affecting prey populations

lizard predators and spider prey with lizards being introduced to some islands

introduced species

a species that is introduced to a region of the world where it has not historically existed

invasive species

an introduced species that spreads rapidly and has negative effects on other species, human recreation, or human economies

parasitoids

live within and consume the tissues of living host, eventually killing it

what can parasitoids also limit

the abundance of their prey

mesopredators

relatively small carnivores that consume herbivores

top predators

predators that typically consume both herbivores and mesopredators

when do mesopredators become more abundant

after a top predator declines

herbivores

organisms that consume part of all of a plant

what can herbivores affect

plant populations

predatory prey dynamics in oranges and mites in the lab

with no predators prey mites reached carrying capacity, with predators prey and predators went extinct, and with greater distance extinction took longer

when did populations cycle in the lab

with barriers to dispersal for predators and dispersal aids for prey populations cycled giving the prey a fighting chance

lotka volterra predator prey model

growth rate = birth rate - death rate

what does death rate of prey depend on

predators

what does birth rate of predators depend on

prey

growth of prey

dN/dt = rN - cNP (n = number or prey, P = number of predators, c = capture probability

growth of predator

dP/dt = acNP - mP (a = the efficiency of a predator converting consumer prey into predator offspring, m = per capita mortality rate of predators)

when is a prey population stable

when its rate of change is 0

stable prey population

r/c = P

what does prey population growth depend on

number of predators

when does the prey population increase

when the predator population is low

low predator population

P < r/c

when does the prey population decrease

when the predator population is high

high predator population prey

P > r/c

when a is a predator population stable

when its rate of change is 0

stable predator population

m/ac = N

what does predator population growth depend on

the number of prey

when does predator population increase

when there are enough prey

enough prey in predator population

N > m/ac

when does the predator population decrease

when there are not enough prey

not enough prey in predator population

N < m/ac

a decrease in the prey population

causes a decrease in the predator population

an increase in the predator population

causes a decline in the prey population

a decrease in the predator population

allows an increase in the prey population

an increase in the prey population

allows an increase in the predator population

when do prey populations decrease

when predators increase

when do predator populations increase

when prey increase

why do predator and prey populations cycle

cycles in pop growth

what does the lotka volterra model not incorporate

density dependence or realistic foraging behavior

functional response

the relationship between the density of prey and an individual predators rate of food consumption

type 1 functional response

linear increase in consumption until saturation

type 2 functional response

decreased consumption with increased prey density

why does type 2 functional response occur

because handling time increases

type 3 functional response

decreased consumption at low and high prey density

why might type 3 functional response happen

refuges, lack of search image, prey switching

numerical response

a change in the number of predators through population growth or population movement due to immigration or emigration, quick response/population regulation

defense against predators

predators cause mortality so there should be frequent natural selection for defense

defense

include behavioral, structural, mechanical, and chemical adaptations

behavioral defenses - alarm calls

warns relatives that predators are approaching

behavioral defenses - spatial avoidance

occurs when a prey moves away from a predator

behavioral defenses - activity reduction

avoid being detected by a predator

crypsis

camouflage that allows an individual to match its environment

structural defenses

reduce a predators ability to capture, attack, or handle prey

defenses against herbivores

induced, constitutive, structural, chemical

induced defense

plastic

constitutive defense

fixed

structural defenses

features such as sharp spines and hairs

chemical defenses

secondary compounds such as caffeine, nicotine, tannins, and glucosinolates

what have many species of insects evolved to chemical defenses

tolerance

warning coloration (aposematism)

chemical defenses evolve in association with conspicuous colors and patterns, aversions to aposematic colors can be innate or learned

batesian mimicry

palatable species evolve to resemble unpalatable species

mullerian mimicry

several unpalatable species evolve to resemble each other

a parasitoid

lives on and consumes its host

which is not true of predators

none of the above because they can influence prey behavior, defenses, population, and evolution

in the lotka volterra model, the death rate of prey depends on

the number of predators

in the classic experiments of C.F. Huffaker using mites and oranges, what mechanisms allowed the predator and prey populations to persist

a varied environment for the predators and prey