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5.1 Evolution 5.2 Species Interactions 5.3 Ecological Communities 5.4 Community Stability

natural selection

process by which individuals that are better suited to their environment survive and reproduce most successfully


generation-to-generation change in the proportion of different inherited genes in a population that account for all of the changes that have transformed life over an immense time

survival of the fittest

a natural process resulting in the evolution of organisms best adapted to the environment

threatened species

a species that could become endangered in the near future

endangered species

a species whose numbers are so small that the species is at risk of extinction

extinct species

a species that was once present on Earth but has died out


animal that hunts and eats other animals


animal hunted or caught for food


species that have disappeared from an area, but still exist elsewhere

habitat loss

the process in which natural habitat is rendered functionally unable to support the species present; leading cause of species decline


inherited characteristic that increases an organism's chance of survival

structural adaptation

a physical feature of an organism's body having a specific function that contributes to the survival of the organism

behavioral adaptation

an inherited behavior that helps an organism survive


an adaptation that allows an animal to protect itself by looking like another kind of animal or like a plant


an automatic instinctive unlearned reaction to a stimulus, an automatic response that occurs very rapidly and without conscious control (playing dead)


a complex behavior that is rigidly patterned throughout a species and is unlearned (migration)


no longer in existence


the number of different species in a given area


relationship in which two species live closely together over a long period of time


symbiotic relationship in which one organism lives in or on another organism (the host) and consequently harms it


symbiotic relationship in which both species benefit from the relationship


symbiotic relationship in which one member of the association benefits and the other is neither helped nor harmed

food chain

series of steps in an ecosystem in which organisms transfer energy by eating and being eaten

food web

consists of the many overlapping food chains in an ecosystem


an organism that makes its own food


an organism that obtains energy by feeding on other organisms


organism that obtains energy by eating only plants

secondary consumer

An organism that eats primary consumers


organism that obtains energy by eating animals


organism that obtains energy by eating both plants and animals

tertiary consumer

An organism that eats secondary consumers


a detritivore that gets its energy by feeding on refuse and other decaying organic matter


organism that breaks down and obtains energy from dead organic matter

trophic level

Steps on a food/biomass pyramid that are defined by organisms within a community that are the same distance from the primary producers in a food web

energy pyramid

diagram that shows the energy available to each trophic level in an ecosystem; 10% is passed on to upper levels, the rest is lost as heat

ecological succession

The gradual and orderly process of change in an ecosystem brought about by the progressive replacement of one community by another until a stable climax is established

primary succession

an ecological succession that begins in a an area where no biotic community previously existed

pioneer species

first species to populate an area during primary succession

climax community

The last or final stage of succession in a community which is in equilibrium with its environment

secondary succession

Sequence of community changes that take place after a community is disrupted by natural disasters or human actions


The concept of using the earth's resources in such they provide for people's needs in the present without diminishing ability to provide for future generations


a sequence of DNA that codes for a particular trait

genetic drift

biological evolution that occurs by chance


describes how reproductively successful an organism is in its environment

artificial selection

process of selection conducted under human direction


process by which new species are generated


the ability to survive and reproduce under changing environmental conditions

resource partitioning

species divide the resource they use in common by specializing in different ways


two species evolve in response to changes in each other


primary producers use energy stored in the bonds of hydrogen sulfide to convert carbon dioxide and water into sugars (energy from chemicals on ocean floor)


cycle the nutrients of nonliving organic matter, including leaf litter, waste products, and the dead bodies of other community members

keystone species

a species with a strong or wide-reaching impact on a community

invasive species

a nonnative organism that spreads widely in a community

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