Chapter 3 - 4

04 Environmental Science

Habitat Fragmentation

Researchers in the field of conservation biology who study factors such as urban development and its effects on ecosystems have focused much attention on habitat fragmentation.

Habitats are said to fragment when they are broken down into smaller habitat patches.

It is typically the result of human activity, such as rural development or agricultural species.

This fragmentation has many effects, which include localized species extinction and so-called “edge effects”.

Edge effects occur when a fragmented habitat borders a contrasting environment, such as developed land.

Habitat fragmentation is a significant cause of localized extinction (the extinction of a species only within a certain area).

Fragmentation increases the risk of predation.

When humans build roads, houses, and buildings, they fragment ecosystems.

This effectively reduces the size of many animal’s hunting and feeding area.

Smaller habitats resulting from habitat fragmentation rarely provide enough cover and food resources for species living there.

For example, the New England cottontail rabbit requires large patches of shrubs (woody plants) as a cover resource.

Without the shrubs to conceal their movements, the cottontail is unable to hide from attacking predators.

Localized extinction is likely.

The numbers of predators, such as raccoons, foxes, and coyotes often increase in a fragmented habitat.

Predators can often more easily adapt to different environments-including the smaller patches of habitat-because they can take advantage of different resources that exist in both the small patches and the developed areas.

To illustrate, a raccoon can find food alongside highways or even in the trashcans of residential areas.

The prey of such animals is then more susceptible to attack as a result of the higher numbers of predators, making localized extinction more probable.

In order for any natural population to survive, it must maintain a “critical number” of whatever species makes up the population.

If animals within that species drop below a certain number, the species will face extinction.

In order to maintain this critical number, the species needs a certain amount of area in which to live.

This minimum area should be great enough in size to compensate for years of bad weather.

For example, animals that live in larger habitats may struggle during seasons or years with poor weather.

They must travel far and wide through the larger area to find the food needed to get through difficult times.

However, in a smaller, fragmented habitat, a harsh winter or a season or two with much lower than average precipitation can kill off a species, as finding food becomes problematic during such times.

Simply put, in smaller areas, there is not enough food to go around during the lean times.

Habitat fragmentation also causes what are known as edge effects.

When a border is created between a natural habitat and developed land, the ecosystem within the natural habitat is affected.

A forest’s where the trees have been cut down.

Sunlight penetrates the former forest’s interior, drying it up more quickly.

The drying-out process then affects the border areas of the remaining forest, causing them to dry out as well.

The forest’s interior is shadier, more humid, and the air more still than at the edges.

The climate toward the edges, on the other hand, is windier and has more sunlight due to its proximity to the developed land, which has been cleared and exposed to more climate changes.

This all has the effect of drying out the edges of forests to a sometimes dangerous degree.

Of course, such edge effects have an impact not only on the plants of an area, but its animal populations as well.

On a micro scale, many insects that live in border areas, particularly those that do not roam far from a home base or migrate, may face localized extinction.

Larger animals, too, feel the edge effects.

They typically move further into the center of the fragmented habitat, since it is nearly impossible for many animals to adapt to the edge effects.

Predators can, of course, sense these movements, and the large numbers of smaller animals that move into the habitat’s center often become easy prey.