The loss of
biodiversity and the related changes in the environment are now faster than
ever before in human
history and
there is no sign of this process
slowing down. Virtually all of
Earth’s ecosystems have been
dramatically
distorted and altered by human activities and
continuously be converted
for agricultural and
other uses. Many
animal and plant populations have declined
in numbers and
geographical spread.
However, species
extinction is a natural part of Earth’s history but human activity has
increased the extinction rate by at least 100 times compared to the natural
rate. Loss of biodiversity is caused
by a range of drivers. A driver is
any natural or
human-induced factor that directly
or indirectly causes
a change in an
ecosystem. A direct driver unequivocally influences
ecosystem processes. An
indirect driver operates more
diffusely by altering one or more direct drivers. Important direct drivers
affecting biodiversity
are habitat
alteration, climate change, invasive species overexploitation and pollution.
Principal threats to
biodiversity
A threat by
definition refers to any process or event whether natural
or human induced
that is likely
to
cause adverse effects
upon the status or sustainable use of any component of biological
diversity. Biodiversity is declining
rapidly due to
factors such as
habitat alteration and
destruction by the land use change, over exploitation of
biological resources, climate
change, pollution and invasive species. Such natural or human-induced
factors tend to interact and amplify each other.
Habitat alteration
and destruction
Overall, the main factor
directly driving biodiversity loss worldwide is
habitat alteration and
destruction.
Habitat destruction
renders entire habitats functionally unable to support the species present in
the habitat.
Biodiversity reduced
in this process when existing organism in
the habitat are
displaced or destroyed.
Human destruction of
habitats has accelerated greatly in the latter half of the twentieth century.
Natural habitats are often destroyed through human activity for the purpose of
harvesting natural resources for industry production and urbanization. Clearing
forest areas for agriculture, changes in the riverine habitat to lacustrine
(reservoir) habitat by the construction of hydroelectric projects on the rivers,
mining, logging, urban sprawl, construction of highways are some examples of
habitat destruction and fragmentation. A five-year estimate of global forest
cover loss for the years 2000–2005 was 3.1 percent.
In the humid tropics
where forest loss is primarily from timber extraction, 272,000 km was
lost out of
a global total
of 11,564,000 km(or 2.4 percent).
In the tropics, these losses also represent the extinction of species because
of high levels of endemism. Increased greedy demand for resources has resulted
into land use changes. Hence loss
to genetic diversity,
species reduction and increased
ecosystem changes such as random population changes,
disease outcrop, and
habitat fragmentation among others
has resulted into biodiversity losses.
Over-exploitation of
biological resources
This results when
individuals of a particular species are taken
at a higher rate than can be
sustained by the natural reproductive capacity of the population being
harvested. This can be through hunting, fishing, trade, food gathering etc.
Overexploitation remains a serious threat
to many species,
such as marine
fish and invertebrates, trees,
and animals hunted for meat. The grazing
pressure on most of the high altitude grasslands of the Uttarakhand state both
from migrant and local
communities, is the
extensive extraction of medicinal herbs in these areas resulting in their over
exploitation. Most industrial fisheries are either fully or overexploited,
while destructive fishing techniques harm estuaries and wetlands. Although the
true extent of exploitation is poorly known, it is clear that rates of off take
are extremely high in tropical forests. The trade in wild
plants and animals
and their derivatives
is poorly documented but
is estimated at
nearly $160 billion annually. It ranges from live animals for
the food and pet trade to
ornamental plants and timber.
Because the trade in wild animals and plants crosses national borders, the effort to regulate it requires international cooperation to safeguard certain species from overexploitation.
Over the past five decades, inorganic and organic pollutants have emerged as one of the most important factor of biodiversity loss in terrestrial, aquatic- marine as well as freshwater ecosystems. Thermal pollution is another threat to biodiversity. The potential consequences of organic pollutants in a freshwater ecosystem include eutrophication of fresh-water body, hypoxia in coastal marine ecosystems, nitrous oxide emissions contributing to global climate change, and air pollution by NO in urban areas. Occurrence of such problems varies widely in different regions. Species in habitats are increasingly being harmed by industrial activities and pollution from excessive use of agro-chemicals such as DDT, oil spills, acid precipitation etc.
The vulture was once very common in the Gangetic plains of India, and often seen nesting on the avenue trees within large cities in the region. Before the 1990s they were even seen as a nuisance, particularly to aircraft as they were often involved in bird strikes. The vulture has suffered a 99% population decrease in India and become rare due to poisoning by DDT used as pesticides and also by
diclofenac which is
used as veterinary non –steroidal anti- inflammatory drug, leaving traces in cattle
carcasses which when
fed by vultures leads to thinning of egg shells resulting into premature
hatching and kidney failure in birds.
The dramatic
decreases in house sparrow population in India is experienced in recent past.
It is linked with
pollution caused
by electromagnetic radiation
from mobile phones. Microwave
towers; the excessive
use of pesticides,
a gradual decrease in nesting sites caused by changes in urban building
design.
Species invasions
This can be
intentional or accidental. Species
introduced in an ecosystem will cause changes in the
ecosystem. Introduced species are organisms arising in areas/ habitats in which they were previously not native. Such introduced species are usually referred to as biological pollutants. Some of the ecological impacts of the invasion include hybridization, out competition, disruption of original ecosystem, plant pathogenic influences, disease transmission, disruption of food-webs, and to some situations extinction. Species may be introduced intentionally for ornamental concerns, agriculture, hunting and spotting activities, biotechnology for scientific research and for trade.
Climatic changes
This is of great
concern especially when global CO2 increases
in the atmosphere resulting to global
warming. Most species
originate within a very narrow physiological limit; hence nature has a range of
tolerance maintained
for ecosystem stability. Changes may
be gradual or
abrupt such that
if the limit
is
exceeded the upper or lower, species suffers extinction.
Recent changes
in climate, such
as warmer temperatures in
certain regions, have
already had
significant impacts
on biodiversity and ecosystem. They have
affected species distributions, population sizes, and the timing of
reproduction or migration events, as well as the frequency of pest and disease
outbreaks. Projected changes in climate by 2050 could lead to the extinction of
many species living in certain limited geographical regions. By the end of the
century, climate change and its impacts may become the main direct driver of overall biodiversity loss. While
the growing season in Europe has lengthened over the last 30 years, in some
regions of Africa the combination of regional climate changes and human
pressures have led to decreased cereal crop production since 1970. Changes
in fish population have also been
linked to large-scale climate variations
such as "El
Nino" have affected fisheries off the coasts of South
America and Africa, and decadal oscillations
in the Pacific have affected
fisheries off the
west coast of
North America.
As climate change wili
become more severe, the harmful impacts on ecosystem services will outweigh
the benefits in most
regions of the world. The
Intergovernmental Panel on Climate Change (IPCC)
project that the
average surface temperature will raise by
2 to 6.4 levels.
This is expected to cause global
negative impacts on
biodiversity (Millennium Ecosystem Assessment, 2005).
Population
From 1950 to 2011,
world population increased from 2.5 billion to 7 billion and is forecast to
reach a plateau
of more
than 9 billion
during the 21st
century (Population
Reference Bureau). As
the human
population is
increasing, there exists insatiable demand for raw materials which is bound to
cause changes in
biodiversity. The
human population has more impact on biodiversity than any other single factor.
According
to Dumont, (2012)
until the middle of the 21st century, worldwide losses of pristine biodiversity
will largely
depend on
the worldwide human birth
rate. It is therefore vital to control human
population which will
result in
biodiversity conservation.
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