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 animals'
hunting and feeding areas. 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 ecosystem may, for example,
be affected when it borders a land 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 Jive 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.
Hiç yorum yok:
Yorum Gönder