(8) Species interactions I

predation

one organism (predator) feeds on another, thereby killing and consuming some portion (or all) of it

Prey

Organism that is killed

herbivory

loss of tissue in plants (typically does not kill the plant), due to grazing by herbivores

Mesopredators

mid-level predators-relatively small carnivores that consume herbivores (e.g. coyotes)

Top predatores

predators that typically consume both herbivores and predators (e.g. mountain lions)

Herbivores can…

1. negatively affect plant fitness (e.g. reduce growth rates)

2. can also promote growth

Specialists

target a few or a single plant species

Generalists

forage on many species

Functional response of predator

the relationship between the density of prey and an individual predator’s rate of food consumption

• Whenever prey density increases and a predator can consume a higher proportion of those prey, the predator can regulate the growth of the prey population.

Type I functional response

• if prey consumption increases linearly with prey density until satiation occurs

• as prey density increases, predators consume a constant proportion of prey until satiation

Type II functional responses

• prey consumption begins to slow as prey density increases and then plateaus at satiation

• any increase in prey density is associated with a slowing rate of prey consumption

• associated with increased handling time-takes time to eat safely

• more prey consumed = more time

Type III functional responses

• when predation rate is low, rapid, and slowing prey consumption under low, moderate, and high prey densities, respectively

Search Image

a learned mental image that helps a predator locate and capture food

stages of predation

the sequence

1. encounter

2. detection

3. identification

4. approach

5. sybduing prey

6. consumption

Encounter

avoiding capture

• prey can leave/avoid area

• enter a refuge (e.g. den)

• active at different times than predator

Detection

avoiding capture

• prey can reduce their conspicuousness—reclusive

• move unpredictably—do not appear as "prey.”

• confuse predators by being in large groups

identification

avoiding capture

• crypsis

• aposematism

• mimicry

crypsis

blending into the backgrouns to avoid detection

aposematism

opposite of crypsis, advertising as a warning.

• synthesis/ingestion of toxix compounds that render organism unpalatable

• honest advertising of toxic condition, typically via bright/striking colour and patterns

Mimicry

1. batesian: one species is palatable (mimic) and the other is not. mimic phenotypically resembles the model

2. Mullerian mimicry: all are toxic/noxious

Approach

avoiding capture

• prey can “outrun” predator or retreat to refuge

subduing prey

• avoiding capture

• fighting back