Chapter 15- Mutualism & Commensalism

Mutualism

Mutually beneficial interaction between individuals of two species

Commensalism

Individuals of one species benefit; individuals of other species do not benefit and are not harmed

Symbiosis

Two species live in close physiological contact w/each other

Benefits of positive interactions

Shelter, food, transport, etc.

Mycorrhizae

Symbiotic associations between the roots and various fungi

Plants supply fungi with

Carbohydrates

Ectomycorrhizae

Fungus grows between root cells and forms a mantle around the root

Arbuscular mycorrhizae

Fungus grows between and penetrates the cell walls of some root cells, forming a branched network called an arbuscale

When both benefit

Facultative mutualism

Costs and benefits vary in

Space and time

RNE

Relative neighbor effect= target species performance with neighbors present minus its performance with neighbors removed

RNE POSITIVE

High elevation sites

RNE NEGATIVE

Low elevation sites

Positive interactions are more common where

Stressful environments

Trophic mutualism

Mutualism receives energy or nutrients from its partner

Habitat mutualism

One partner provides shelter, living space, or favorable habitat

Service mutualisms

One partner performs an ecological service for the other

Mutualisms are not altruistic

True

To be mutualism

Net benefits must exceed net costs for both partners

Facultative

Two organisms can, but don’t have to live with each other

Obligate

Both symbionts depend on each other for survival

Cheaters

Individuals that increase offspring production by over exploiting their mutualistic partner

Penalties

Mutualist may withdrawl or modify the reward, reducing or removing advantage if cheating

Dominant species can

Determine distributions of other species by providing habitats