ch 15: predation

consumption of one living organism by another

what is predation

predator

an animal that naturally preys on others

prey

an animal that is hunted and killed by another for food

- true predators

- herbivores

- seed predators

- planktivores

- parasites

types of predation

true predators

typically kill their prey and consume most of what they kill

herbivore predators

feed on prey without killing

seed predators

animals that chew up or digest plant seeds

planktivores

aquatic animals that feed on planktonic food

parasites

an organism that lives in or on another organism, deriving nourishment at the expense of its host, usually without killing it

- predator and prey each function as a density dependent regulator of each other

- population sizes matter and will be regulated

describe predators and prey

through mortality

how do predators regulate prey populations

by influencing rates of reproduction

how do prey regulate predator populations

Lotka-Volterra predator-prey model

a modified form of the logistic equation used to model predator-prey interaction cycles

- the slope of line (c) increases

- as prey population increases, number of prey consumed (predation) increases

- as prey increase, predation increases

describe the relationship between prey population and number of prey consumed per unit time

efficiency of predation

what does c represent

efficiency of food conversion to offspring

what does b represent

- the slope of line (b) increases

- as the number of prey consumed increases, the number of predator offspring increases

- as predation increases, reproduction increases

describe the relationship between number of prey consumed per unit time and number of predator offspring produced per unit time

prey increase

what happens if the Npred is below r/c

prey decrease

what happens if the Npred is above r/c

predators decrease

what happens if the Nprey is below d/bc

predators increase

what happens if the Nprey is above d/bc

- the predator has no food, so it cannot survive

- the prey is not being eaten, so the prey numbers increase

- prey increase, predators decrease

what happens at low prey and low predator populations

- there are many predators which feed on the prey

- the predators have plenty of energy to reproduce

- predators increase, prey decreases

what happens at high prey and high predator populations

- the predators have plenty of prey to feed on, so they have energy for reproduction

- the prey are in high numbers and there are not many predators feeding on them

- predators increase, prey increase

what happens at high prey and low predator populations

- there are not many prey so the predators cannot increase

- the there are more predators than prey feeding on the prey

- rey decrease, predators decrease

what happens at low prey and high predator populations

- they are linked, and rise and fall in oscillations

- the predator follows the prey

describe the dynamics of predator and prey

- the lynx is the predator

- the hare is the prey

- there were records of buying fur each year

- as the prey (food source) rises and falls in numbers, the predator follows

- when the prey is low, the predators decrease, when prey is high, the predators increase

example of predator prey dynamics with the lynx and hare

- cover or refuges for the prey (prey must hide from predators)

- difficulty of locating prey as it becomes scarcer (less prey, less likely to find it)

- choice among multiple prey species

- coevolution (as predators get better at catching prey, prey get better as escaping predators)

what are factors other than mutual regulation that influence predator prey interactions

functional response

the relationship between the density of prey and an individual predator's rate of food consumption

the relationship between the per capita predation rate and prey population size

- predators response to increasing prey numbers

what is functional response

functional response type I

linear increase in consumption rate as food densities rise, until reaching a maximum consumption rate

- linear, constant predation

- prey increase, predators increase

- ex. passive predators, lay in wait predators, filter feeders

- OR prey is never abundant enough to fill predators

describe functional response type I

functional response type II

the rate of prey consumption by a predator rises as prey density increases, but eventually levels off at a plateau at which the rate of consumption remains constant regardless of increases in prey density

- most common

- as prey increase, predators increase up to a certain point

- prey number is so abundant that predators needs are met

describe functional response type II

functional response type III

number of prey taken is initially low, then increases in a sigmoid fashion approaching an asymptote

- as prey increases, initially predation rates are low, then increase in a sigmoid curve manner

- predation rates are low then increase until needs are met

describe functional response type III

- availability of cover

- search image

- prey switching

why might functional response type III occur

- susceptibility of prey individuals increases as prey population grows because hiding places become filled

- the more prey there are, the less hiding places, and the more likely they will be found

describe why availability of cover would cause type III response

- ability of predator to recognize prey will increase as prey population increases

- as prey increase, predators get better at recognizing them and knowing what to look for

describe why search image would cause type III response

- predators utilize a different prey in the area as it becomes more abundant

- predators may ignore one prey at low numbers, then switch when the prey are in higher numbers

describe why prey switching would cause type III response

prey switching

a predator may strongly prefer a certain prey but may switch to a more abundant species it can hunt more profitably

search image

as foragers (or predators) encounter potential food items (or prey), they develop an enhanced ability to recognize those items in the future when they are foraging (or hunting)

availability of cover

the susceptibility of prey individuals will increase as the population grows and hiding places become filled

expected rates of predation

- predation may not be linear

- predations rates start out low, then increase as prey increase

what can prey switching affect

the predator population should respond positively (increase)

- through reproduction by predators (predators have more energy for reproduction)

- through aggregative response (predators move to where prey are abundant)

what happens as Nprey increases

aggregative response

movement of predators into areas of high prey density

movement of predators into areas of high prey density

what is aggregative response

- as prey numbers increase, the number of nesting pairs increase

- there are more predators raising offspring

what is the relationship between number of larvae (prey) of budworms per unit and number of nesting pairs by the predators (warblers)

- as prey numbers increase, the mortality due to predators decreases

- there are more prey, so more are likely to survive

what is the relationship between number of larvae (prey) of budworms per unit and mortality due to predators (warblers)

- considers the trade offs between conflicting demands

- natural selection should favor "efficient" foragers who maximize their energy or nutrient uptake per unit of effort (animals should be efficient at taking in food sources)

what is the optimal foraging theory

- feeding (what to eat, where to find it, how to get it)

- reproduction (gamete production, mate selection, parental care)

- survival (avoiding injury and predation, being vigilant)

what might be some trade offs and demands for time

- out of different prey (bird) lengths, there were the most available of 8 mm

- the 7 mm prey were selected much more frequently

- when predators eat the 7 mm prey, it is most efficient at intaking more calories per second

- although there are more larger prey available that might be more total calories, the smaller ones are more efficient

example of trade offs with birds

- function to preserve smarter and more evasive prey

- produce smarter more skilled predators

what should natural selection do

coevolution

process in which two or more species evolve in response to changes in each other

as prey species evolve ways to avoid being caught, predators evolve more effective means to capture them (better prey = better predators)

what is coevolution

- chemical defense

- cryptic coloration

- object resemblance

- warning coloration

- mimicry

- protective armor and weapons

- behavioral defenses

examples of coevolution of prey

chemical defense

compounds released by prey to defend themselves from predators

- bees stings produce alarm pheromones

- skunks release odorous secretions

- butterflies and plants have toxins or poisons

examples of chemical defense

cryptic coloration

camouflage that makes a potential prey difficult to spot against its background

colors and patterns that allow prey to blend into the background to try to avoid predators completely

what is cryptic coloration

object resemblance

an organism resembles an object in the environment to avoid detection from predators

- a type of cryptic coloration

- organism blends into environment by looking like an object in the environment

- ex. stick bug, leaf bug

describe object resemblance

warning coloration (aposematism)

conspicuous coloration or markings of an animal serving to warn off predators

- prey send a warning signal to predators

- aka aposematism

- can also be scent or sound

- ex. rattlesnake sound, brightly colored poisonous organisms

describe warning coloration

batesian mimicry

a type of mimicry in which a harmless species looks like a species that is poisonous or otherwise harmful to predators

- an edible species mimics an inedible species to ward off predators

- predators ignore both species, but both species must be present for this to work

- ex. coral snake (inedible) and king snake (edible) have similar coloration; rat snakes and king snakes mimic the rattling sound of rattlesnakes

- can be coloration, sound, smell, behavior

describe batesian mimicry

mullerian mimicry

two or more unpalatable species resemble each other

- similar color pattern shared by many unpalatable or venomous species

- all carry threat and have similar color patterns

- ex. black and yellow repeating stripes of harmful arthropods, different species of millipedes share the same coloration

describe mullerian mimicry

- exoskeletons of insects

- shells in molluscs, turtles, armadillos, pangolins

- horns, antlers, tusks, claws

- spines, quills, thorns

examples of protective armor and weapons

behavioral defense

organisms have developed behaviors that attract less attention, such as reduced movement or hiding

- warning signals (bird chirps)

- vigilance

- distracting predators

- mobbing (smaller birds harass birds of prey while resting)

- defensive grouping (muskox grouped, facing predators with young or injured in back)

examples of behavioral defense

constitutive defenses and induced defenses

two classes of predator defenses

constitutive defenses

defensive traits by plants or prey that are expressed even when there are no predators

induced defenses

responses that are directly stimulated by an attack from predators

fixed features (defenses) of the organism that are always present regardless of whether a predator is around

- ex. warning coloration

describe constitutive defenses

defenses or features brought about by the presence or action of predators

- ex. alarm pheromones, cacti spines

describe induced defenses

- ambush hunting

- stalking

- pursuit hunting

- venom/antivenom

examples of coevolution of predators

ambush hunting

lying in wait for prey to come along

- lying in wait for prey to come

- low frequency of success

- low energy cost

describe ambush hunting

- deliberate form of hunting with a quick attack

- search time is great but pursuit time is minimal

- spend long times getting close to prey but attack quick

- ex. wading birds, lions/ antelope

describe stalking

- involves minimal searhc time (the predator usually knows the location of the prey) but considerable pursuit time

- ex. wolfs/deer

describe pursuit hunting

- coevolution

- predators with venom (ex. snakes)

- prey develop antivenom in response (ex. rodent)

describe venom/antivenom