L1 Predation

Grazing

Low probability of death for the victim and a short duration of interaction

• Eating parts of the organism

• Ex. zebra eating grass, mosquito drinking blood

• Creates habitats like grasslands

• Can stop certain species from taking over, leading to more diversity

Predation

High probability of death for the prey, short interaction

• Ex. wolves eating a deer, carnivorous plants, seed _____

• A structuring force in the natural community

• A major driver of adaptive evolution

Parasites

Low probability of death for the victim, long interaction

• Ex. ticks

Parasitoids

High probability of death for the victim, long interaction

• Ex. wasp larvae that grow in a bug and kill it before emerging

• Parasites that kill the host

Type 1

Functional response

• A linear increase in intake rate with prey density

• Not very realistic in most systems

• Ex. filter feeders (mussels etc)

Type 2

Functional response

• Incorporates handling time

• Increases quickly to start, but then levels off

• If the caribou density increases whilst the number of wolves is held constant, the number of caribou killed per wolf first increases, then levels off

Type 3

Functional response

• S-shaped curve (low kill rate at low densitites, rapid increase at moderate, leveling off at high)

• Implies switching between different types of prey

  • Ex. generalist predators

  • Switching can occur when:

    • The most common prey is easiest to pursue, capture or handle (learning plays a part)

    • The predator can develop a search image

    • Each individual can switch between prey types, or there are alternative specialists that vary in frequency

Search image

A “visualization” of the prey item the animal is looking for. Makes it easier to identify that item but may lead to overlooking other prey items

Handling time

Time it takes to hunt, eat and digest a prey item before doing it again

• Ex. snakes have a very long ________ for prey items while a bird might eat many bugs quickly

Negative density (/frequency) dependence

Prey benefits from the density being low

• Preserves diversity by benefitting lower frequency groups/populations

• Ex. predators having a preference for the most common prey type

Positive density (/frequency) dependence

Prey benefits from density being high

• Ex. cicadas, aposematism and mimics

Nonconsumptive effects

Effects of predators on prey that are not eating

• Happen just by presence of predators in the area

• Defensive behaviours like hiding more, being more vigilant, less time/energy spent on eating/reproducing

• Improved defense → lower attack rate at lower prey densities → greater stability in the predator-prey interaction

Life-dinner principle

the prey is running for its life, whereas the predator is running for its dinner

• Results in an asymmetry in selection pressure in prey vs. predator

Primary defenses

Defenses that are deployed before the prey encounters the predator

• Ex. crypsis, disruptive colouration, avoiding being in the same places as predators

• Predator satiation

  • Years with unusually high prey densities → low predation risk for each individual

  • Ex. cicada life cycle, mast years in oak

Secondary defenses

Defenses that are deployed post-encounter with a predator

• Ex. induced hiding (due to presence of predators), aposematism (showing signs of poison), mimicry (Mullerian or Bayesian), induced defense

Mullerian

Mimicry where many species develop the same true signal that they are yucky or poisonous

• Sharing common predators

• Mutual benefit

• Ex. some butterflies

Batesian

Harmless species (mimics) deter by falsely imitating a toxic/dangerous species (model)

• Similar phenotype

• Only works if the model is present in the area

• Ex. coral snake mimics

Induced defense

Organisms that modify their body shape in response to predator risk

• Ex. crucian carp, snails, hawthorn

• Evolution depends on

  • Variability in predator pressure, the defense being costly and efficient cues for detecting predators in the environment

Ungrazed

Species that cannot handle grazing

• Ex. ringbarking of trees, spread of disease (elm disease), repeated defoliation

Compensation

Mechanisms to withstand some grazing

• Mobilization of stored resources

• Increased photosynthesis

• Maintaininga constant root:shoot ratio

• Breaking of bud dormancy (activating lower buds)

• Basal meristems (in grasses)

  • Growing from the bottom

Overcompensation

Plants that do better with moderate grazing than none

• Ex. putting out more shoots if they are grazed than if they aren’t

Grazing defense adaptations

• Mechanical

  • Constitutive (always present) or induced (triggered by attack)

  • Ex. spines, thorns

• Chemical

  • Ex. toxins, hard to digest, unpalatable

  • Inducible chemical defense

    • Defense triggered by herbivory activity

    • Synthesis of secondary metabolites

    • Emitted substances that attract enemies of the herbivore