Consumer-Resource Interactions: Herbivory, Predation, Parasitism

Consumer-Resource Interaction

One species exploits another, one benefits while the other species is harmed.

Predation

A type of Consumer-Resource interaction where one species benefits (+) and the other species loses out (-).

Herbivory

A herbivore grazes live plant material, but does not typically kill the plant.

Parasitism

A parasite lives on the tissue of another organism (host) and reduces the host's fitness but does not typically kill the host.

Obligate host

A type of parasitic life history where the parasite needs a host to survive.

Facultative host

A type of parasitic life history where the parasite can survive without a host.

Accidental host

A type of parasitic life history where the parasite can't complete its life cycle.

Amensalism

One species negatively affects another species, but does not gain immediately from the interaction.

Consumer influence

Consumer species can greatly influence the abundance and distribution of its resource.

Dynamic Consumer-Resource Interactions

The Consumer influences the abundance of Resources, and the abundance of Resources influences the abundance/behavior of Consumers.

Predator-Prey Cycles

The cyclical pattern of predator and prey populations, typically stable but can be affected by environmental disturbances.

Trophic Cascade

Interactions between consumers and resources that are appreciated when considering all trophic levels.

Snowshoe Hare and Lynx

A classic example of predator/prey interaction.

Size Selected Predation

The complexity of predator-prey relationships, such as the relationship between Snowshoe hares and their environment.

Snowshoe hares habitat

Snowshoe hares live among spruce, jackpine, tamarack, balsam poplar, aspen, and paper birch trees.

Snowshoe hares diet

Snowshoe hares eat the buds of various trees, as well as stems of roses and willow trees.

Predators of hares

Goshawks, great horned owls, mink, weasels, red foxes, and coyotes.

Lotka-Volterra model

A model for cyclic predator-prey interactions.

Growth of prey population

[the intrinsic growth rate of the prey population] - [the removal of prey individuals by predators].

dNh/dt

rhNh - pNhNp

rhNh

Exponential growth by host/prey population.

p

Rate of parasitism / predation.

Nh

Number of hosts/prey.

Np

Number of parasites / predators.

Consumer population growth rate

[rate of conversion of food into offspring] - [mortality rate of consumer population].

dNp/dt

cpNhNp - dpNp

cpNhNp

Rate at which consumer species converts food (resource species) into offspring (c = conversion factor).

dpNp

Death rate of consumer species.

Elements of reality not incorporated in the model

Time lags in predator/prey response, carrying capacities for predator and prey populations, no functional response in predator.

Destabilizing factors for predator-prey cycles

Some destabilizing factor must be present to drive the system (e.g., time delay in the response of population to a change in its food supply).

Stabilizing factors

Predator inefficiency, density-dependent limitation on either predator or prey population by external factors, alternative food source for the predator, refuges for the prey at low prey densities, reduced time delays in predator responses to changes in prey abundance, influx of new replacement individuals from source population.

Refuge

An exploited population requires a refuge for cyclic predator-prey pattern to exist/persist.

Example of a refuge

A groundhog hiding in a burrow, a flock of pigeons, a mayfly pretending to be a spider, or a mussel being too big for a seastar to eat.

Types of Refuge

Space, Numbers, Morphology, behavior/morphology, size.

Size-selection predation

Pisaster sea-stars eat mussels, but if mussels can survive to a large size they can become too big for sea-stars to eat.

Nt

N0 λt

dN/dt

rN

dN/dt (with carrying capacity)

rN (1-N/K)

dN1/dt

r1N1(K1-N1-α12N2/K1)

dN2/dt

r2N2(K2-N2-α21N1/K2)