EXPLORING BIODIVERSITY: A Guide for Educators Around the World

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important differences,
however, between
these extinctions and
the one many scientists
say we’re facing today.
One difference, according
to conservation biologists,
is that today’s
extinction spasm is
occurring more
rapidly than those of
the past—especially for plant
species. Another difference
scientists point to
is that the potential for
species and ecosystems to recover from this episode
of extinction is probably far lower than with past
episodes. That’s because, in the past, certain species
have escaped extinction by surviving in pockets of
habitat that happened to be relatively unaffected
by natural catastrophic events. Species that survived
a global extinction episode in these refuges
were able to gradually recolonise surrounding areas
when conditions became more favourable. But
today, many potential refuges are being destroyed
or degraded by human activity. Many scientists
worry that even if conditions do eventually
improve, we have already lost too much habitat
and genetic diversity to allow ecosystems to
recover. Never before on our planet has one species
been responsible for such a massive decline of
global biodiversity.
Losing Ground
The loss of habitats—the places where organisms
live and get the nutrients, water, living space, and
other essentials they need to survive—is the
primary reason biodiversity is in decline. When
people cut down a forest, fill in a wetland, trawl
a seabed, or plough a grassland, they change the
natural habitat of the species that live there. Not
only can such changes kill or force out many animals,
microorganisms, and plants, but they also
can disrupt complex interactions among species.
Often, habitats aren’t so much destroyed outright
as they are chiselled away little by little. When
not carefully planned, agricultural fields, roads,
houses, mining operations, and other
modifications fragment natural areas, forming a
patchwork of habitat islands in a sea of
development. For some species, this “sea” is a
barrier that isolates them from sources of food or
water. It can also isolate species from others of
their kind, resulting in inbreeding and a loss of
genetic diversity.
Habitat fragmentation can cause
other problems too. For example,
when a road is built through a forest,
areas that were once in the
forest’s interior become exposed
to more light, wind, and temperature fluctuations.
Animals that are adapted to conditions
inside forests often can’t tolerate these changes
and are forced to move elsewhere, if they can.
Plants, which can’t just pick up and move, may
die out.
In the long run, habitat destruction can disrupt
human communities as well as those of plants and
animals. For example, a few people in a community
will make money by cutting trees for timber.
However, once those trees are gone, the community
might face more problems with erosion and
flooding, making it more and more difficult to
grow food for their families or to sell at markets.
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