Biodiversity is affected by many things:
• Climate: The impact of changing climate
is likely to have impacts on biodiversity. See the climate change
page for more detail. Earthwatch
is conducting research into the impact of climate change on biodiversity.
• Fire, a natural component of many ecosystems,
effects animal populations. Earthwatch
is conducting research into the impact of fire on ecosystems in
• Natural disasters such as earthquakes and
• Human activities are placing pressures
on biodiversity and in many instances leading to losses in diversity.
Biodiversity fluctuation is natural. Ecosystems are dynamic and
over time the numbers and densities of species will vary. Species
will be lost and new species will evolve. This is natural change.
However big fluctuations in biodiversity today are commonly accepted
to be due to human use of resources and human activities. The impact
of humans is dealt with in this section. For more information on
the political and economic reasons for biodiversity loss visit WWF’s
Macroeconomics for Sustainable Development Office website
Direct use of natural resources
Exploitation of Natural Resources has pushed some species to the
verge of extinction.
• Exploitation of animals has left many species threatened,
including the tiger, elephants and Black Rhinoceros.
• Marine stocks have been dramatically reduced as fishing
methods improved and the quantities harvested from the sea increase.
• Many habitats are being lost due to deforestation in order
to meet growing demands for wood as well as other materials found
in forested areas.
Habitat loss and Fragmentation
For centuries, landscapes have been altered by humans through deforestation,
fire and over-use. The result is often a simplification of habitats
that has led to the local loss and ultimate extinction of species
and an overall loss of biodiversity.
Habitat loss is identified as a main threat to 85% of all species
described in IUCN
Red Lists. Fragmentation of habitats can expose the interiors
of remaining habitat to edge effect, which benefits some species
but harms many others.
Small fragments of habitat can only support small populations of
fauna and small populations of fauna are more vulnerable to extinction.
Fragments of habitat that are separated from each other are unlikely
to be recolonised. Also many birds and mammals need large areas
in which to feed and breed.
The inside of a habitat has a different climate and supports different
species to the edge. Small fragments of habitat do not contain this
interior habitat. Habitat along the edge of a fragment has a different
climate and favours different species to the interior. Small fragments
are therefore unfavourable for those species which require interior
habitat and may lead to the extinction of those species.
When native vegetation is cleared for agriculture, urban developments
or roads, habitats which were once continuous become divided into
separate fragments. After intensive clearing, the separate fragments
tend to be very small islands isolated from each other by areas
unsuitable for wildlife.
Deforestation is one of the leading causes of habitat
and biodiversity loss. As tropical forests contain at least half
of the Earth's species, the clearance of some 17 million hectares
each year is causing a dramatic loss of biodiversity. As the world
population exceeds six billion people, the pressure on land for
building and agriculture, in particular, add to concerns for biodiversity
Oceans, rivers, lakes and lands have become repositories for society’s
industrial and organic waste. Pollutants entering our environment
travel through the food web increasing in concentration in the tissues
of animals further up the food chain. This can reduce survival and
lower reproductive success of many species. Amphibians, for example,
are key indicators of ecosystem health. Scientists have found that
commonly used chemicals such as pesticides, herbicides and fertilizers
are decimating frog populations. The reduced abundance and diversity
of frog species are a warning signal about the impacts of pollution.
Large volumes of pollution overwhelm the Earth’s capacities
to absorb, transform or break down these materials. Some materials
take thousands of years to decay, and may become more toxic as they
decompose, resulting in long-term environmental damage.
Eutrophication is a major problem in many water systems where agricultural
waste and fertilizers run off the land and into rivers and lakes.
The increased nutrient content in the water causes excessive algal
growth reducing the amount of light which enters the water leading
to an increase in anaerobic bacteria activity and reduced oxygen
content in the water. The lowered levels of oxygen make the water
unlivable for many plants and animals.
An "alien" or "exotic" species is one that
occurs in an area outside its historically known natural range as
a result of either intentional or accidental dispersal by human
activities. Sometimes, alien plants or animals become established
in their new environment and spread unchecked, threatening native
biodiversity. Invasive exotic species have been identified as the
second greatest threat to biodiversity after habitat loss.
When a new species is introduced - accidentally or not - in an
area, it can have major impacts on native species that have evolved
no defences against such invaders. Natural barriers to the movement
of certain plants and animals provide the isolation which resulted
in unique species and ecosystems evolving. Island species are often
the most vulnerable because they will have been isolated from other
species for long periods of time and developed high levels of endemism.
The Convention on Biological Diversity includes an article specifically
calling for the prevention, control, and eradication of alien species
that threaten ecosystems, habitats, or species.
In the 1970’s the Louisiana Crayfish was introduced to Lake
Naivasha in Kenya to provide a boost for the local fishermen. The
crayfish produced good yields for the first few years after introduction
but then started to severely affect the food chain in the lake.
is being conducted into the impacts of the Crayfish on the lakes
ecosystem by Earthwatch.
Visit the Invasive
Species Specialist Group (ISSG) part of the World
Conservation Union (IUCN) for more information on invasive species.
Photo credit: nile Crocodile eye, Leslie