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The primary threat to species worldwide is habitat degradation and loss—with perhaps the most dramatic example being the clearing of millions of acres of tropical rain forest. However, the loss of even a relatively small area can still significantly disturb species such as the golden-cheeked warbler by fragmenting remaining habitat. Large, continuous tracts of habitat, especially in urban areas like Austin, are broken up into smaller, isolated patches by new development and construction. For instance, the building of a road across a grassland divides that habitat into separate sections.

The surrounding edge of a habitat fragment that borders development or construction is abrupt and unnatural, creating a highly altered environment. This edge habitat is preferred by generalist species such as raccoons, opossums, and blue jays that are adapted to living and feeding in both developed and undeveloped areas. These edge species can often be seen in neighborhoods as well as in the Preserve. Conversely, many native plants and animals are adapted to specialized conditions and thus prefer areas of undisturbed habitat that are found in the interior of fragments. For instance, wildflowers that grow in shaded areas will not be found near the edge due to the exposure to direct sunlight. As habitat is divided into smaller fragments, the amount of edge habitat increases, making these interior species more vulnerable to invasive species and predators found along the edge—an impact known as the “edge effect.”

Another negative effect of habitat fragmentation is that it can limit the movement of species by creating open areas and roads that many birds, mammals, and insects will not cross. Animals that do venture into the open are exposed to dangers such as hawks, domestic cats, and traffic. This limitation can often confine animals to one isolated fragment. However, many of these smaller fragments may not be able to support certain species that require relatively large tracts of habitat for survival. For example, animals at the top of the food chain like bobcats and foxes require large tracts of habitat to hunt for prey and establish territories. These top predators, critical to controlling the white-tailed deer population, are rarely seen in the Austin area anymore.