Slide Set 7 Predation

What is predation?

Members of one species consume all or part of another species or each other

How do species interact through predation?

Species interact (+, −) directly by predation

How can predation affect prey populations?

It can reduce prey abundance or alter distribution

What question is asked about predators and prey dynamics?

What role do predators have in driving the dynamics of their prey populations?

What are the five basic types of predation?

Carnivory, parasitism, parasitoids, cannibalism (intraspecific predation), herbivory

What model describes predator-prey interactions?

Lotka–Volterra Predator–Prey Model

What assumption is made about prey in the absence of predators?

Prey populations grow exponentially

What is the prey population growth equation without predators?

dN/dt = rN

What is the prey population growth equation with predators?

dN/dt = rN − (C P N)

What does P represent in the prey equation?

Number of predators

What does N represent in the prey equation?

Number of prey

What does C represent in the prey equation?

Search and attack efficiency of the predator

What determines the number of prey consumed?

The encounter rate and predator efficiency

What is the consumption rate of prey?

C P N

What counteracts prey consumption in predators?

Predator birth rates

What determines predator birth rates?

Rate of prey consumption and conversion efficiency

What is predator conversion efficiency (g)?

Efficiency of turning food into offspring

What assumption is made about predators in the absence of food?

Predator populations decline exponentially

What is the predator decline equation without prey?

dP/dt = −d2P

What does d2 represent?

Mortality rate

What is the predator population growth equation?

dP/dt = g C P N − d2P

What characterizes predator-prey equations?

Populations oscillate

Are predator-prey oscillations stable?

Neutrally stable

What determines oscillation amplitude?

Starting conditions

Why don’t populations cycle indefinitely in nature?

Environmental conditions continually change

Why do predator-prey oscillations occur?

Time delays in predator and prey responses

What is the total population size of toads at the start of year 2?

0

How many new recruits were added to the toad population?

−100

What prey species is used in the practice problem?

Arroyo toads

What predator species is used in the practice problem?

Red-sided garter snakes

What is the initial toad population size?

100

What is the initial snake population size?

6

What is the per capita growth rate of toads (r)?

0.2

What is the predator attack efficiency (C)?

0.2

What is the prey population growth equation used?

dN/dt = rN − (C P N)

What is the population size of snakes at the start of year 2?

28.8

What is the snake mortality rate (d2)?

0.2

What is the predator conversion efficiency (g)?

0.2

What is the predator population growth equation used?

dP/dt = g C P N − d2P

How many snake recruits were added at the end of year 1?

22.8

What laboratory experiment first tested the predator-prey model?

Gause (1934)

What organisms were used in Gause’s experiment?

Didinium (predator) and Paramecium (prey)

What happened in Gause’s experiment?

Predator exterminated prey and then died

What was the result of Utida’s 1957 experiment?

Population cycles occurred

What organisms were used in Utida’s experiment?

Azuki bean weevils and parasitic wasps

How long did the oscillations last in Utida’s experiment?

112 generations

How many oscillations occurred in Utida’s experiment?

14

What happened to host and parasite populations?

Host increased and parasite decreased

What outcomes are predicted with model modifications?

Equilibrium, oscillations, extinctions

What predator introduction affected the Great Lakes?

Sea lamprey (Petromyzon marinus)

What type of parasite is the sea lamprey?

Anadromous marine ectoparasite

What event allowed lamprey into the Great Lakes?

Construction of the Welland Canal

What fishery was decimated by lamprey?

Lake trout

When did lamprey control efforts begin?

1951

When did lake trout populations recover?

2004

Do predators influence prey abundance in nature?

Yes

Are clear predator-prey cycles common in nature?

No

What is a classic natural predator-prey cycle example?

Snowshoe hare and lynx

What is the period of the hare-lynx cycle?

Approximately 10 years

Where is the hare-lynx cycle observed?

From Alaska to Newfoundland

Why do hare populations decline?

Lower birth rates and increased predation

How does plant availability affect hare populations?

Reduced food increases exposure to predators

What generates the hare-lynx cycle?

Hare-plant and hare-predator interactions

How do prey populations persist?

Refuges, predator behavior, and adaptations

What are chemical defenses?

Toxins often paired with warning coloration

What is camouflage?

Cryptic coloration and mimicry

What other antipredator strategies exist?

Intimidation, agility, armor, altered reproduction

What is masting?

Altered reproductive patterns to overwhelm predators

What is a prey refuge?

Spatial or temporal protection from predators

What is optimal foraging?

Predators switch prey when prey become scarce

What determines population abundance?

Intrinsic and extrinsic factors

What intrinsic factors affect population size?

Natality, mortality, dispersal

What extrinsic factors affect population size?

Abiotic and biotic factors

What abiotic factors affect populations?

Physical and chemical conditions

What biotic factors affect populations?

Predation, competition, herbivory, symbiosis

What resources affect populations?

Nutrients and space

What individual-level factors affect populations?

Physiological and behavioral traits

What ultimately changes population numbers?

Density