Fragmentation of a habitat, by its very nature, reduces the total amount of
area of the original habitat type. Two researchers, Ann Keller and John
Anderson suggest that the absolute habitat loss of pristine habitat and the
reduced density of resources associated with fragmentation potentially impacts
the biota (the plant and animal life of a region) more than any single factor.
Habitat fragmentation affects the flora and fauna (plants and animals) of a
given ecosystem by replacing a naturally occurring ecosystem with a
human-dominated landscape which may be inhospitable to a certain number of the
original species. However, in direct contrast to the ocean as a geographic
barrier, the human landscape matrix is typically accessible to plants and
animals, in that they are able to easily disperse across it, if not reside in
it.
On the other hand, the human landscape may directly contribute to the
extinction of species by slanting the ecosystem balance of species which are
highly adaptable to changing conditions. For example, the increased amount of
human-dominated landscape allows certain species to grow phenomenally, which
can result in harm to species which rely exclusively on very scarce areas . A
commonly referred to example of this is a bird called the brown-headed
cowbird. This bird is best characterized as a ?nest parasite? because it
because it replaces the eggs of another species with eggs of their own ,
allowing the other species to incubate and raise their young. Their increased
numbers have had negative effects on the reproductive successfulness of many
forest-dwelling birds.
In addition to titling the ecosystem balance in favor of species which are
highly adaptable, the loss of habitat associated with habitat fragmentation may
simply cause the other, less adaptable species rates to decline. A man named
James Saunders documents one remarkable example of how changing large expansive
areas of the birds of the wheatbelt of western Australlia as a result of
fragmentation. He showed that 41% of the birds native to the region have
decreased in range or abundance since the 1900?s and indicated that almost all
of these changes resulted directly from habitat fragmentation and the decline
in abundance of native vegetation. Although some species have increased in
abundance, he noted that many more species have been adversely affected than
have benefited.
Importantly, the species that typically increase in abundance or range when
habit fragmentation occurs are those which are adapted for being adaptable. In
other words, their resource needs can be met by a variety of conditions, and
thus often by human activities by reducing their competition with other
species. Because of this, these species which benefit by human activities are
not the ones we need to manage for and protect. Instead, we need to protect
those species which are adapted solely for survival in the rapidly disappearing
unfragmented habitat.
Besides physically changing a part of the original habitat, decreasing the size
of the original habitat can reduce the biological diversity of an area in
several ways. Reducing biodiversity of an area may occur if habitat fragments
are smaller than the home range of the animal with the largest home range that
existed within the intact ecosystem. Many birds have large home ranges because
they require patchily distributed resources. For example, one breeding pair
of ivory billed woodpeckers require five to six square miles of undisturbed
contiguous bottomland forest, and a single European goshawk requires twenty to
forty-five miles for his home range.
If a habitat fragment exists that is smaller than the minimum area required by
a given species, individuals of that species will not likely be found within
that habitat fragment. For example, the Louisiana waterthrush is rarely found
in small woodlots because they require open water within their home range, and
most small woodlots do not have year-round streams or ponds. If a species
requires two or more habitat types, they are often susceptible to local
extinction due to habitat fragmentation, because often they are unable to
freely move between the different habitat types. The blue-grey gnathatcher
moves from decidous woodland to chapparral (a warm area) during the breeding
season, and if one of the two habitat types can not be readily accesed, they
are very susceptable to local extinction.
Loss of any species from a community may have secondary effects that revrberate
throughout the ecosystem. For example, loss of a top predator from an area
because the fragment is too small can cause numbers of small omnivores to
increase, which in turn may cause excessive predation pressureon songbird eggs
and hatchlings, ultimately resulting in reproductive sucess.
Tropical communities are oftem more susceptable to loss of biological diversity
than temperate communuities, because tropical species typically are found in
lower densities, are less widely distributed, and often have weaker dispersal
capabilities. Many tropical species have evolved in that they have changed
their roles that they play in the rainforest. An example of this occurance is
the cassowary, an Austrailan rainforest frugivore, (or an animal that primarily
feeds on fruit) is extremely susceptable to local extinction by habitat
fragmentation because its habitat requirement of large coniguous rainforest
areas is compounded by its unique plant-seed despersal evolvment. This large,
flightless bird wanders nomadically in search of very large seeds, many of
which need to be digested before they will germanate. You?lll rember that
earlier another example of this situation in which the dodo bird became
extinct. The dodo bird digested seeds of the calvaria tree. But when the dodo
bird became extinct due to overhunting by humans, the calvaria tree, which made
the seeds to be digested by the dodo bird to sprout it?s plants started not to
sprout seeds. In the Rainforests, their are many such instances like this.
But unfortunately, many of them go unnoticed and thus, each day many of the
rainforest plants and animals go extinct.
Besides being home to extinction-prone species, tropical communities are prone
to destruction and fragmentation because of their physical location,
overlapping with the geographical birders of the third world nations. In
these nations, citizens often rely on the revenues raised from rainforest
timber or cattle raised on cleared land for survival. This constant pressure
on rainforest communities leads to excessive habitat fragmentation. Small
isolated fragments result, leading to an altered ecosystem balance. On the
tropical island of Java, where almost all of the original habitat remaining
exists in reserves, a group of ecologists have assessed the status of all of
the birds of prey found in the rainforest habitat. Nearly all the raptors were
extremely rare outside the reserves, as expected. They also found that the
larger the reserve was, the denser the birds populations were within the
reserve.
Interestingly, a scientist named Lovejoy (I couldn?t find his first name) in
1986 found a similar phenomena with Amazonian birds in the Biological Dynamics
of forest project (BDFF) in Brazil. The primary goal of the project is to
discover how rainforest communities respond after an intact ecosystem is split
into different size fragments. They found a crowding effect, in which the
abundance of birds in a forest fragment increased significantly directly after
deforestation of the adjacent area. The increased number of birds was
attributed to the migration of birds from the newly clear-cut area to the
forest fragment. This crowding effect decreased with increasing size of a
forest fragment.
Both tropical and temperate communities, however, are prone to the same
problems of inbreeding and loss of genetic variability, which results from
isolating subpopulations of plants and animals from each other due to habitat
fragmentation. If too large a distance exists between two fragments and a
species are unable to disperse across the area in between, the population is
essentially divided. Inbreeding may result if the subpopulation in a given
fragment is small. This has not been directly documented, but it is possible.
Size of a fragment and the amount of edge are inextricably linked. Abrupt
edges often results form fragmenting and ecosystem, in contrast to the more
gradual natural ecotones. Edge positively impacts many species of plants and
animals, but as mentioned previously, the species which benefit typically are
those which do not require human protection and management because they can
easily meet their resource need outside of the intact ecosystem. The
scientists from the BDFF project point out one exception. Tamarins and
marmosets, both species in need of protection , flourish in small tropical
rainforest reserves because of the luxurian growth of early successional plant
species, and the lack of large predators which are unable to exist in the
smaller reserves. Certainly , a system of only small reserves would not
suffice to protect the genetic heritage of biological diversity in the tropical
rainforest, but a heterogeneous mosaic of large and small reserves may provide
the best alternative.
Although edge has typically been associated with an increase in species
richness, researchers are increasingly documenting how edge effects negatively
impact the native plants and animals. The BDFF researchers pointed out that
although the number of species may be higher in edge that the adjacent interior
habitat, species diversity is usually not. Diversity takes into account not
only raw number of species, but the relative abundance of the species present.
Another potentially adverse effect of edge is that it inherently reduces the
size of the habitat interior because of the many physical changes which occur
where and edge is compared to a human dominated area. Most documented cases of
edge effects are from forest edges, so I will focus on them. In addition to
the luxuriant growth of shade-intolerant vegetation at a forest edge in
response to the increase in available light, a ?seed rain? bombards the forest
interior, often from introduced exotics. The increased exposure to wind causes
a higher rate of treefalls and tree mortality, and temperature and humidity are
quite different at the edge than in the forest interior. These physical
changes affect the plants and animals of the habitat. Lovejoy and others, in
the BDFF project in Brazil, found that the understory birds tend to avoid
artificial edges. They found 38% fewer birds 10 meters from clearing than 50
meters into the forest, and 60% fewer birds 10 meters from a clearing than 1 km
into undisturbed forest. An interesting item is that they did not find a lower
abundance of birds around natural edges, such as interior treefall gaps.
Several authors that I have read have suggested that the abundance of birds
decreases near an artificial edge due to decreased Nest success. Nest success
near edge decreased because of the increase in generalist predators and brood
parasites. As mentioned earlier, populations of brown-headed cowbirds, a brood
parasite, have increased tremendously as a direct result of human activity,
these birds have a negative impact on the nesting success of forest songbirds
that nest near the forest edge. Studies show that while vegetational changes
may extend from 300-600 meters into a fragment. This makes sense when one
considers that although generalist predators such as raccoons, cowbirds, and
chipmunks may concentrate their activity near the edge, they certainly also can
frequent the forest interior, often to the damage of those species which rely
exclusively on forest interior.
To reduce how far edge effects penetrate into a natural habitat, a biologist
Bernard Harris, proposed a system of long-rotation islands, in which and
old-growth center is surrounded by various age stands of timber. This system
provides some edge for those species which benefit from it, while minimizing
the amount of edge between the old-growth center stand and the surrounding
stands.
Now, to the final section of this term paper, the role that environmentalists
play and some of the reasons that they are trying to save it.
Rainforests cover less that two percent of the Earth?s surface, yet they are
home to some 40 to 50 percent of all life forms on our planet, as many as 30
million species of plants, animals, and insects. The Rainforests are quite
simply, the richest, oldest, most productive, and most complex ecosystems on
Earth. As biologist Norman Meyers notes, ?Rainforests are the finest
celebration of nature as ever known on the planet, and never before has
nature?s greatest orchestration been so threatned.?(4)
His quote is quite true. The following facts listed are direct proof of how
the Tropical Rainforests are being depleted.
Global Rates of Destruction
2.4 acres per second: equivalent to two U.S. football fields
149 acres per minute
214,000 acres per day: an area larger than New York City
78 million acres per year: an area larger than Poland
In Brazil
5.4 million acres per year
6-9 million indigenous people inhabited the Brazilian rainforest in 1500. In
1992, less than 200,000
Species Extinction
Distinguished scientists estimate and average of 137 species of life forms are
driven into extinction every day or 50,000 each year.
While you were reading the above statistics, approximately 90 acres of
rainforest were destroyed. Within the next hour approximately six species will
become extinct. While extinction is a natural process, the alarming rate of
extinction today, comparable only to the extinction of the dinosaurs, is
specifically human-induced and unpreceeded. Experts agree that the number one
cause of extinction is habitat destruction. Quite simply, when habitat is
reduced, species disappear. In the Rainforests, logging, cattle ranching,
mining, oil extraction, and hydroelectric dams all contribute to rainforest
destruction and produce many undesired effects in the environment such as
global warming, depletion of the ozone layer, and depletion of the earth?s
natural resources.
But now, there may be some help for the rainforest. Until recently, few
vacationers would even dream of visiting a rainforest. But travelers are now
abandoning the traditional beach vacation to visit remote, unspoiled areas all
over the world. They try to avoid the fast pace and congestion of the
traditional tourist centers, opting instead for more adventure, stimulation and
a desire to learn while on vacation. This growing trend of travel has come to
be known as ecotourism.
Though there are many definitions of ecotourism, the term is most commonly used
to describe any recreation in natural surroundings. The Ecotourism Society
adds social responsibilities to define ecotourism as ?purposeful travel to
natural areas to understand the culture and natural history of the environment,
taking care not to alter the integrity of the ecosystem, while producing
economic opportunities that make the conservation of natural resources
beneficial to local people?(5)
However defined, ecotourism is a force shaping the use of the tropical
Rainforests. This will be even more true in the future due to ecotourism?s
rapid growth. Global tourism is one of the largest industry in the world and
ecotourism is the fastest growing segment of the industry.
Tourism is largely responsible for saving the gorillas of Rwanda from
extinction. The gorilla was threatened by both poachers and local farmer,
whose land clearing practices were destroying the gorillas? natural habitat.
Rwanda?s Parc des Volcans, created by Dian Fossey as a wildlife preserve, has
become an international attraction and the third largest source of foreign
exchange for Rwanda. Revenues from the $170-a-day fee that visitors will pay
to enter the park have allowed the government to create anti-poaching patrols
and employ local farmers as park guides and guards. Even this success is
danger from the civil war that is encroaching and endangering both the forest
and tourist industry.
If ecotourism is going to be influential in saving Rainforests, income from
tourism must reach the people who will ultimately decide the forest?s future.
Unfortunately, too often the money generated does not benefit these people.