Predation

Snowshoe hares and Canada lynx predators

Snowshoe hares constitute a major portion of lynx diet

Historical trapping data from the Hudson’s Bay Company indicate that numbers of both hares and lynx fluctuated in a 10-year cycle

Hare survival rates are highest several year before hare density peaks and fall and do not rise again until several years after hare density peaks —> change in food supplies

Main concern…predation

Chronic stress: response is maintained for long periods; can affect growth and reproduction and susceptibility to

Trophic vs Non-trophic

Interactions of evolutionary change can be based on feeding (trophic) or on space/resources (non-trophic, like competition).

Symbiosis

A specific type of interaction where species live in close physical or physiological contact. This can be positive (mutualism), negative (parasitism), or neutral.

Competition

two or more species overlap in the use of limiting resources

Mutualism

Both species benefit (e.g., pollinators and flowers)

Commensalism

One benefits, the other is unaffected

Amensalism

One is harmed, the other is unaffected (e.g., an elephant stepping on ants).

Competition

Both species are harmed by the shared use of limiting resources

Predation

an individual of one species (predator) consuming individuals or parts of another (prey).

Carnivory

Both predator and prey are animals

Herbivory

The predator is an animal; the prey is a plant or algae

Parasitism

predator (a parasite) lives symbiotically on or in the prey (its host) and consumes certain tissues; may not kill the host

Most carnivores have ___ diets, whereas most herbivores

have relatively ___ diets.

broad; narrow

Predation results in a wide range of ________ mechanisms

capture and recapture

Most carnivores have broad diets, whereas a majority of herbivores have relatively narrow diets – why?

Optimal Foraging Theory: theory: encounter rate vs. handling

time

Generalist: mostly carnivores, encounter rates and handling times are low

Specialist: mostly herbivores, encounter rates and handling times are high

Mechanism for Predators:

1. Find prey

   1. MOVE AROUND

   2. AMBUSH

   3. SET TRAP

2. Capture prey

   1. BURST OF SPEED

   2. MORPHOLOGICAL CHARACTERISTICS

   3. POISON

   4. MIMICRY

   5. ETC

Mechanism for Prey:

1. Avoid being eaten

   1. Physical features

   2. Warning coloration

   3. Crypsis

   4. Mimicry

   5. Behavioral Adaption

      1. Trade-offs

The Landscape of Fear

wolves make roadways safer, generating large economic returns to predator

conservation

an ecological concept describing how prey animals perceive and react to predation risk, creating a "map" of high-risk (peaks) and low-risk (valleys) areas that shapes their behavior.

Mechanisms for prey (plant edition):

1. Avoid being eaten

   1. PRODUCE HUGE NUMBER OF OFFSPRING

   2. STRUCTURAL DEFENSES

   3. CHEMICAL DEFENSES

   4. INDUCED DEFENSES

      1. COMPENSATIVE GROWTH

      2. INCREASING EXISTING DEFENSES

Mechanisms for Predator (who eats plants edition):

1. Avoid being eaten

2. Digest plants

   1. DIGESTIVE ENZYMES

   2. BEHAVIORAL AVOIDANCE

   3. AND MORE!!!

Predator-prey cycles

If there are no predators, what happens to prey? → exponential growth

What slows prey growth? → encounters with predators

If there's no prey, what happens to predators? → exponential decline

What helps predators grow? → encounters with prey

Lotka–Volterra predator–prey model

Prey Growth: In the absence of predators, the prey population is assumed to grow exponentially.

Predator Decline: In the absence of prey, the predator population is assumed to decrease exponentially at a specific mortality rate.

Interactions: Prey growth is slowed by encounters with predators, while predator growth is fueled by encounters with prey

For prey population…

When P = 0, the prey population grows exponentially.

• With predators present (P ≠ 0), rate of prey capture

depends on how frequently they encounter each other

(NP) and efficiency of prey capture (a)

For predator population…

If N = 0, predator population decreases exponentially at death rate d.

When prey are present (N ≠ 0), individuals are added to the predator population according to the number of prey killed (aNP) and efficiency (b) of conversion of prey into more pre

Cycling

When these isoclines are combined, they reveal that predator and prey populations tend to cycle around a neutrally stable equilibrium point where the two lines cross.'

Population cycles are difficult to achieve in the lab

Predators can change the outcome of competition, affecting distribution or abundance of competitor species

If a predator or herbivore decreases performance of the top competitor, the inferior

competitor may increase in abundance.

Ex: Paine (1974) removed starfish

predators from a rocky intertidal zone.