Community Interactions

Community

• All the populations that live together in a habitat

• Habitat is the type of place where individuals of a species typically live

• Type of habitat shapes a community’s structure

Factors Shaping Community Structure

• Climate and topography

• Available foods and resources

• Adaptations of species in community

• Species interactions

• Arrival and disappearance of species

• Physical disturbances

Niche

Sum of activities and relationships in which a

species engages to secure and use resources

necessary for survival and reproduction

Species Interactions

• Most interactions are neutral; have no effect

on either species

• Commensalism helps one species and has no

effect on the other

• Mutualism helps both species

Species Interactions

• Interspecific competition has a negative effect

on both species

• Predation and parasitism both benefit one

species at a cost to another

Symbiosis

• Living together for at least some part of the

life cycle

• Commensalism, mutualism, and parasitism are

forms of symbiosis

Mutualism

• Both species benefit

• Many examples in nature

• Some mutualisms are obligatory;

partners depend upon each other

Yucca and Yucca Moth

• Example of an obligatory mutualism

• Each species of yucca is pollinated only by one

species of moth

• Moth larvae can grow only in that one species

of yucca

Mycorrhizae

• Obligatory mutualism between fungus and

plant root

• Fungus supplies mineral ions to root

• Root supplies sugars to fungus

Improved water and mineral uptake in mycorrhizal plants.

Commensalism

• One species benefits other is not

harmed

• Many examples in nature

Predation

• Predators are animals that feed on other

living organisms

• Predators are free-living; they do not

take up residence on their prey

Prey Defenses

• Camouflage

• Warning coloration

• Mimicry

• Moment-of-truth defenses

Predator Responses

• Any adaptation that protects prey may select

for predators that can overcome that

adaptation

• Prey adaptations include stealth, camouflage,

and ways to avoid chemical repellents

Parasitism

• Parasites drain nutrients from their

hosts and live on or in their bodies

• Natural selection favors parasites that

do not kill their host too quickly

Types of Parasites

• Microparasites

• Macroparasites

• Social parasites

• Parasitoids

Hog Sphinx Moth caterpillar, seen here on Smartweed, has been parasitized

by Cotesia congregata, a braconid that lays its eggs in the caterpillar

Cobweb Spider (plus Ichneumonid wasp parasite)

Balanophora fungosa produces no chlorophyll so it is unable to manufacture

its own food from sunlight so it lives parasitically on the roots of certain plants.

Immature Spined Assassin bug with what looks like

tachinid egg parasites.

Hyalophora cecropia caterpillar

Immature Spined Assassin bug with what looks like

tachinid egg parasites.