INTRODUCTION

Each organism in an ecosystem requires a habitat of sufficient size to find food, grow, and reproduce. Some species require large ranges and may become extinct if their habitats shrink.

Humans are continually encroaching on the world's natural habitats. We log forests for wood, replace forests and grasslands with agricultural plots, or eliminate these habitats to accommodate urban sprawl. As human activity destroys habitats, an important question to ask is how much of a natural ecosystem must be left intact for the resident species to continue to thrive? That is, do small patches of habitat adequately preserve the various species, or must these species have access to large, undisturbed regions? Do corridors between patches allow species in the patches to persist over time?

In the accompanying animation, we depict experiments in which researchers test the effects of habitat fragmentation and the presence of corridors on the extinction of species.

CONCLUSION

Although a moss-covered rock is a tiny ecosystem, the principles of species survival and extinction learned from it can be extended to larger ecosystems, such as forests or grasslands. Because individuals of the species that live in the moss are very small and move over only short distances, for them, the rock and its moss patches represent a large ecosystem.

Most of the species living on the mossy rock were affected by habitat fragmentation. A full 40 percent of species populations became extinct, and most of the species that survived the fragmentation were less abundant in the patches than in the control region. This experiment took place over the course of a year, which was equivalent to many generations for most of the arthropod species.

In their second experiment with the rock ecosystem, the researchers examined the effect of corridors on species extinction. They found that if fragmented patches were connected to the mainland by thin strips of habitat—the corridors—they retained as many species as the mainland. The researchers surmised that the corridors allowed species to disperse between patches. If a species died out in one patch, individuals from the mainland could migrate into it and repopulate the patch. However, if the corridors contained gaps, more species disappeared in a patch, presumably because individuals could not easily migrate from the mainland.

Habitat fragmentation threatens the survival of many of the species that live in a habitat. However, if fragmented habitats are connected by corridors through which individuals can move, they can continue to support most of the species that live in them.

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Textbook Reference: Concept 42.6 Ecology Provides Tools for Conserving and Managing Populations