Predation, Parasites, and Consumer–Resource Interactions (3)

What is exploitation?

A (+/–) interaction where one species benefits and the other is harmed.

What is predation?

A trophic interaction in which a predator kills or consumes prey.

What is carnivory?

A form of predation where both predator and prey are animals.

Why are carnivores usually generalists?

Animal prey are nutritious but rare, so predators benefit from broad diets.

What is herbivory?

A form of exploitation where predators are animals and prey are plants or algae.

Why are herbivores often specialists?

Plants have structural and chemical defenses requiring specialized adaptations.

Why are plants low-quality food?

Plants are low in protein and high in fiber.

What is a physical defense?

A structural trait that reduces capture or kill probability.

Example of physical defense: size

Large animals deter predators by being difficult to attack.

Example of physical defense: speed

Some prey have morphology specialized for rapid escape.

Example of physical defense: armor or spines

Prey use shells or spines for protection.

What is a chemical defense?

Use of toxins or distasteful compounds to deter predators.

What is warning coloration?

Bright coloration that signals toxicity (aposematism).

What is Batesian mimicry?

A harmless species mimics a toxic one.

What is crypsis?

Camouflage used to avoid detection by predators.

What is compensatory growth?

Herbivory stimulates increased plant growth or flowering.

What is a structural plant defense?

Physical plant traits such as thorns, spines, hairs, or tough leaves.

What are inducible defenses?

Plant defenses that increase after herbivore attack.

What are secondary metabolites?

Plant chemicals used for defense but not required for basic metabolism.

Example of a secondary metabolite

Capsaicin.

Example of a secondary metabolite

Caffeine.

Example of a secondary metabolite

Tannins.

How can herbivores overcome secondary metabolites?

By evolving detoxification or tolerance mechanisms.

What is the growth-defense tradeoff?

Plants cannot simultaneously maximize growth and defense.

What is parasitism?

A (+/–) symbiotic interaction where a parasite feeds on a host without necessarily killing it.

What is a pathogen?

A parasite that causes disease.

What is an ectoparasite?

A parasite living on the surface of its host.

What is an endoparasite?

A parasite living inside the host’s body.

Advantage of ectoparasitism: dispersal

Easier dispersal between hosts.

Advantage of ectoparasitism: immune avoidance

Less exposure to host immune defenses.

Disadvantage of ectoparasitism: feeding

Feeding on the host surface is difficult.

Disadvantage of ectoparasitism: environment

High exposure to environmental conditions.

Disadvantage of ectoparasitism: predators

Increased vulnerability to natural enemies.

Advantage of endoparasitism: feeding

Easy access to host tissues for feeding.

Advantage of endoparasitism: protection

Protection from external environment.

Disadvantage of endoparasitism: dispersal

Difficult to move to a new host.

Disadvantage of endoparasitism: immunity

High exposure to host immune system.

Why do parasites evolve lower virulence?

Killing the host reduces transmission; moderate virulence increases fitness.

What virus was used to control rabbits in Australia?

Myxoma virus.

Why did the myxoma virus become less lethal?

Host resistance increased and the virus evolved optimal, not maximal, virulence.

How can parasites alter host behavior?

They can manipulate feeding, movement, boldness, or predator avoidance.

How can parasites influence communities?

They change host fitness, abundance, or species interactions.

Why do parasites have complex life cycles?

To maximize transmission through multiple hosts and environments.

What is top-down control?

Higher trophic levels regulate the abundance of lower trophic levels.

What is bottom-up control?

Primary producers regulate higher trophic levels through resource availability.

Why is the world green?

Predators limit herbivores, preventing overgrazing.

What effect do plants have on herbivores?

Positive; they provide energy and biomass.

What effect do carnivores have on herbivores?

Negative; they consume herbivores.

Do ecosystems operate strictly top-down or bottom-up?

Neither; both control types operate together.

What is a trophic cascade?

An indirect predator effect transmitted through herbivores to plants.

Classic trophic cascade effect

Predators decrease herbivores, leading to increased plant biomass.

If predators are removed, what happens?

Herbivore populations increase and plant biomass decreases.

If predators are added, what happens?

Herbivore populations decrease and plant biomass increases.

What is a green world?

A system with abundant vegetation because predators strongly limit herbivores.

What is a brown world?

A system with low vegetation because herbivores are released from predation.

How does disturbance affect cascades?

Disturbance often reduces predators, shifting systems toward brown-world states.

What determines food chain length?

Productivity, ecosystem size, and disturbance.

How does high productivity affect food chain length?

High productivity supports more trophic levels.

How does ecosystem size affect food chain length?

Larger ecosystems can support more species and more trophic levels.

How does disturbance affect food chain length?

Disturbance eliminates top predators and shortens food chains.

Why is food chain length shorter in brown-world systems?

Top predators decline or disappear.

What happened to wolf populations after reintroduction?

Wolf populations increased.

What happened to elk populations after wolves returned?

Elk populations decreased.

What happened to willow populations after wolves returned?

Willow abundance increased.

Why did vegetation increase after wolf reintroduction?

Reduced grazing and elk avoidance of high-risk areas.

What is the landscape of fear?

Behavioral changes in prey caused by fear of predators.

How did elk behavior change after wolf reintroduction?

Elk avoided riverbanks and open areas.

How did behavior changes affect vegetation?

Reduced browsing allowed woody plants to regenerate.

Why is Yellowstone a trophic cascade example?

Wolf reintroduction altered herbivore behavior, plant communities, and ecosystem structure.

What are two lessons from Yellowstone?

Species interactions shape whole communities, and effects can be trophic or behavioral.

In the LV predation model, what does P represent?

Predator population density.

In the LV predation model, what does V represent?

Prey (victim) population density.

In the LV predation model, what does m represent?

Predator per-capita death rate.

In the LV predation model, what does r represent?

Prey per-capita birth rate.

In the LV predation model, what does α represent?

Prey death rate due to predation.

In the LV predation model, what does β represent?

Predator reproduction per prey consumed.

Write the LV predator equation.

dP/dt = -mP + βVP

Write the LV prey equation.

dV/dt = rV - αVP

What does the term -mP represent?

Predator mortality independent of prey density.

What does the term +βVP represent?

Predator birth rate based on prey consumption.

What does the term rV represent?

Exponential prey growth.

What does the term -αVP represent?

Prey losses from predation.

Do predators self-regulate in LV predation?

No; there is no density-dependent term.

Do prey self-regulate in LV predation?

No; prey grow exponentially without predators.

What shape do LV predator-prey dynamics produce?

Stable limit cycles.

Why do predator-prey cycles occur?

Time lags between prey growth and predator response.

What happens if predators temporarily decline?

Prey increase until predator population rebounds.

What happens if prey temporarily decline but do not reach zero?

Predators decline and the system returns to oscillation.

What happens if prey reach zero?

Both prey and predators go extinct.

Equilibrium prey abundance in LV predation

V* = m / β

Equilibrium predator abundance in LV predation

P* = r / α

Why does prey abundance determine predator abundance?

Predators depend entirely on prey for reproduction.

How can predators affect prey besides killing them?

They cause behavioral and habitat-use changes.

What is a non-trophic predator effect?

Any predator effect not involving consumption, such as fear.

How can parasites interact with predation?

They alter host vulnerability or predator efficiency.

How can parasites increase community diversity?

By suppressing dominant competitors.

Why can parasites change competitive outcomes?

They reduce fitness of competitively superior species.