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If you sat by this woodland pond for a few minutes, you’d observe a variety of organisms. The pond is surrounded by different tree species and is bordered by tall grasses. Dragonflies skim over the water, and the call of birds can be heard through the trees. Fish occasionally swim to the surface of the pond to catch insects, and a mass of frog spawn can be seen attached to the reeds.
This tranquil and poetic scene is more than a random grouping of animals and plants. To the ecologist, it is a community—a group of species living in close proximity with the opportunity for interaction.
Some communities, like our woodland pond, are very rich and diverse in the number of organisms they contain. Others, like the hot water springs and geysers of Yellowstone National Park, may contain just a few species of heat-loving bacteria. The relative abundance of different organisms in a community is called the community's species diversity.
Most communities are dynamic – some species die out or leave the community, and new species evolve or immigrate to the community. The proliferation of a species into a new community is called radiation.
Genetic modifications that allow an organism to become more fit to live in a particular community are called adaptations. If an adaptation allows an organism to move into or colonize other communities, the process is called adaptive radiation. Adaptive radiation is a mechanism that has enabled organisms to spread throughout the world, occupying all the habitable ecosystems on our planet.
In this activity, we’ll look at the structure of communities, asking why particular combinations of organisms form communities.
We’ll then see how plants and animals interact within a community by studying some specific examples.
Finally, we’ll examine the dynamics of communities. We’ll see that some communities are very stable, while others may be periodically disrupted by forest fires or by human intervention.
Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education