Lecture 10: Predation and Herbivory

How does predation work?

predators obtain energy and nutrients by killing and eating prey

What do herbivores consume?

producers, such as plants and/or algae

Generalists

select and eat a wide variety of food items

specialists

feeding upon a single species or a restricted range of closely related species

predators and herbivores can limit what?

the abundance of species

Explain this graph: spider densities on the Caribbean islands with and without lizards

The islands with lizards seem to have less number of spiders than the islands without lizards

Explain what this chart mean

snowshoe hares and Canada lynx predators exhibit population cycles of 9-10 years, with lynx cycles lagging about 2 years behind the hare cycles

the synchrony of population cycles between predators and prey suggests that?

oscillations are the result of interactions between them

Predator-prey cycles: Decline of predators

—> increase of prey

Predator-prey cycles: Increase of prey

—> more food for predators —> increase of predators

Predator-prey cycles: more predators

—> decline of prey

Predator-prey cycles: decline of prey

—> lower survival and reproduction of the predator

what does this figure illustrate

predator population size lagging behind prey abundance

What are some predator hunting strategies

Active hunting strategies and Ambush hunting strategies

Active hunting strategies

predators spend most of the time moving around looking for prey

Ambush (sit-and-wait) hunting strategies

wait for a potential prey to pass by

What are some behavioral defenses?

• alarm calling

• spatial avoidance

• reduction of activity

• mobbing

Alarm calling

warning relatives: predators are approaching

spatial avoidance

potential prey moves away from predator

reduction of activity

to avoid being detected by a predator

Mobbing

surround and attack predator

Explain this graph.

• the tadpoles and activity levels

What is crypsis? (behavioral defense)

camouflage that either allows an individual to match its environment or breaks up the outline of an individual to blend in better with the background

Chemical defenses can what?

deter a predator

Explain how bombadier beetles use chemical defenses.

bombadier beetle mixes two chemicals from separate glands to make a boiling-hot liquid that it sprays to either kill or injure predators

Chemical defenses are often more effective at deterring predators if??

the prey can convey the dense before an attack occurs

what is warning coloration (aposematism)?

distastefulness evolves in association with very conspicuous colors and patterns

What is batesian mimicry?

• mimicry of chemical defenses

• palatable species evolve warning coloration that resembles unpalatable species

what is Müllerian mimicry?

• mimicry of chemical defenses

• several unpalatable species evolve a similar pattern of warning coloration

What is an example of Müllerian mimicry?

several species of poison dart frogs have evolved similar warning coloration

Herbivores can have substantial effects on what?

the species they consume

Explain this graph.

The klamath weed abundance in comparison to the beetle abundance. More beetles= less weeds

What is an example of herbivores having a substantial effect on the species they consume?

a beetle has eliminated 99% of the Klamath weed population in North America

what is one example of herbivores regulating populations (deers and plants)?

long term fencing to prevent deer herbivory, resulted in much greater amount of plant growth in Canadian National Park

what is one example of herbivores regulating populations (sea urchins and algae)?

removal of sea urchin from a rocky shore habitat, resulted in biomass of different algae increase

Pressures from herbivores equals what?

evolution of plant defenses

What is an example of structural defenses?

sharp spines, “hairs”

What is an example of chemical defenses?

sticky resin and latex compounds and alkaloids (e.g., caffeine, nicotine, morphine) with a wide range of toxins

Are parasitoids predators or parasites?

they have characteristics of both

What does a parasitoid do?

parasitoids larva lives on or in the host (usually another insect) slowly consuming or killing it

unique type of predation, can limit what?

abundance of prey

explain this illustration

parasitoid uses host (caterpillar) to inject eggs and larva begins to eat host