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

Periwinkle on Seaweed (worksheet study)

Competition Interspecific – between different species Intraspecific - between members of the same species Intraspecific competition is most intense

Forms of Competition Competitors may have equal access to a resource; compete to exploit resource more effectively One competitor may be able to control access to a resource, to exclude others

Competitive Exclusion Principle When two species compete for identical resources, one will be more successful and will eventually eliminate the other

Paramecium caudatum Paramecium aurelia

Competitive Exclusion Expt Paramecium caudatum Paramecium aurelia

Predation Predators are animals that feed on other living organisms Predators are free-living; they do not take up residence on their prey

Coevolution Natural selection promotes traits that help prey escape predation It also promotes traits that make predators more successful at capturing 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

Tarantula Hawk Wasp

Tarantula Hawk Wasp in action!