If you looked across a landscape from the top of a mountain, you would see a patchwork of different communities—say, forests, meadows, lakes, streams, and marshes (FIGURE 19.3).

You could be sure that each of those communities would have a different species richness and composition. The meadows would be dominated by a variety of grasses, herbs, and terrestrial insects.

The lakes would be filled with various species of fish, plankton, and aquatic insects, and they might possibly harbor as many species as the meadows. Even though some species (such as amphibians) would be able to move from one community to another, the communities would still be highly distinct.

FIGURE 19.3 A View from Above Looking at these mountains in Glacier National Park, Montana, it is easy to see that the landscape is made up of a patchwork of communities of different types. View larger image

How do collections of species end up coming together to form different communities? One way to answer this question is to consider the factors that control species membership in communities. If you think about the sheer number of species that coexist within any community, it is clear that no one process is responsible for all the species we find there. As we saw in Concepts 9.3 and

18.1, the distributions and abundances of organisms are dependent on three interacting factors: (1) regional species pools and dispersal ability (species supply), (2) environmental conditions, and (3) species interactions. We can think of these three factors as “filters” that act to exclude species from (or include them in) particular communities (FIGURE 19.4). Let’s briefly consider each of them in more detail.

FIGURE 19.4 Community Membership: A Series of Filters Speciesendupinalocal community by passing through a series of “filters” that determine community membership. Species are lost at each filter, so local communities contain a fraction of the species in the regional pool. In practice, all the filters work at the same time, rather than in series as the figure suggests.

Would it make sense for the fish and frog species in the regional pool to be present in the local community shown in the figure? Explain.

(After J. H. Lawton. 2000. In Community Ecology in a Changing World, O. Kinne [Ed.], Excellence in

Ecology, Vol. 11. Ecology Institute: Luhe, Germany.) View larger image

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Source: Bowman W., Hacker S.. Ecology. 6th ed. — Oxford University Press,2023. — 744 p.. 2023

If you looked across a landscape from the top of a mountain, you would see a patchwork of different communities—say, forests, meadows, lakes, streams, and marshes (FIGURE 19.3).

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