Community Interactions

Chapter 40

Habitat Place where you would normally

find an organism. It is characterized by the temperature, physical features, chemical features, and other species living in it.

Directly or indirectly all of the species in one will associate with one another as a community.

CommunityEach organism within a community

has a sum of activities and relationships in which it engages to secure and use the resources necessary for survival and reproduction.

This is an organism’s niche.

Species Interactions Neutral relationships – where organisms

do not affect each other directly. Indirectly they may affect each other.

Example: Canadian lynx and grass. Commensalism – directly helps one

organism without affecting the other. Example: Birds use trees for

roosting.

Species Interactions cont… Mutualism – interacting species both

benefit from the association. Example: Flowering plants and pollinators.

Obligatory – individuals of one species cannot grow or reproduce without the other. Example: Yucca plants cannot be pollinated

by anything besides a yucca moth.

CompetitionDisadvantages flow both ways between

species. While one organism may be the winner

of the competition, it will still be injured in the process.

Predation Where one animal feeds upon another.

Predators feed on prey, but do not take up residence on or in them. 1. Many predator and prey relationships arose

by coevolution, where two species exert selection pressures on each other because of close ecological interaction.

2. These relationships depend on carrying capacity, the maximum number of individuals that resources can maintain indefinitely.

Parasitism One organism takes up residence

in or on another living organism called the host.

The parasite will feed upon the tissues of the host, and may or may not cause death. Parasites drain hosts of nutrients causing a weakened condition.

This weakened condition can make the host an appealing candidate for predation, but a less than appealing candidate for reproduction.

Natural selection tends to favor a parasitic relationship that does not kill the host, and allows the parasite to reproduce.

Types of ParasitesEctoparasites – live on host’s surface.Endoparasites – live inside a body.Microparasites – small parasites such

as bacteria, viruses, protozoans, and sporozoans.

Macroparasites – large parasites such as flatworms, roundworms, fleas, and ticks.

Competitive Interactions Intraspecific – competition of organisms

within a species. Interspecific – competitions among

different species. Competitive Exclusion – two species

requiring identical resources cannot coexist indefinitely.

Resource partitioning – subdividing of resources that let species coexist

Defense Mechanisms Camouflage –

adaptations in form, coloring, pattern, or behavior that help organisms blend in to their surroundings.

Warning ColorationConspicuous

patterns that warn predators to stay away. Example: Skunks.

Mimicry Many prey bear

resemblance to dangerous organisms. One species serves as a mimic to the other, more dangerous species. Viceroy on left,

Monarch on right

Ecological Succession A community develops in sequence,

from pioneer species (opportunistic colonizers of vacant habitats) to an end array of species that remain in equilibrium over some region.

More competitive species will replace the beginning species until the array of species stabilizes and results in the climax community.

Primary SuccessionWhen pioneer species colonize a

barren habitat. Generally, these species are small

plants with brief life cycles. Once established, the pioneers improve the conditions of the area and replacement species can enter.

Secondary SuccessionA disturbed area in a community

recovers and moves toward the climax state.

InstabilityAn outcome of forces that lead

to an uneasy balance is called community stability.

If these forces are disturbed, it can hurt the growth of some populations.

If the instability is great enough, the community can change in ways to help its survival.

If a species cannot adapt, it may become extinct.

Works Citedwww.naturalsciences.org/

images/skunk.jpg static.howstuffworks.com/ gif/animal-

camouflagwww.ci.san-luis-obispo.ca.us/

naturalresources