Geology Reference
In-Depth Information
entire, a whole host of dung beetle species, large and small, killed off parasites, buried
seeds and ensured that precious nutrients were quickly recycled as they fed their under-
ground larvae on buried dung. But in the forest fragment there is little dung around, for
most of the monkeys and birds that provided it in abundance before the forest was frag-
mented died or left a long time ago. Now there are fewer kinds of dung beetle, and those
that remain are smaller and not very numerous. The dung beetle extinctions happened in
many ways. Hot, dry winds searing in from the pasture outside the fragment wiped out
several species by killing off their larvae. For many species there just weren't enough
mates to go around, and the inhospitable pasture prevented other beetles from colonising
the fragment, to boost numbers and bring in new blood. The consequences for the frag-
ment's remaining denizens have not been good. There are more diseases amongst the
few birds and mammals that remain, nutrients are washed away by heavy rains before
roots can capture them, and the seeds of many plants have not been able to germinate.
Seemingly insignificant, the dung beetles of the Amazon are major players in their eco-
logical community— they are one of the
keystone species
of the forest.
I
ntroduced species
: These can cause extinctions even in areas where there has been
very little habitat fragmentation, and wipe out more species than pollution, popula-
tion pressures and over-harvesting put together. They come from all over the world:
the goats, pigs, cats, rabbits and many others, brought to places they could never have
reached without the help of humans. About 4,000 exotic plant species and 2,300 exotic
animal species have been brought to the United States alone, threatening 42% of spe-
cies on the endangered species list and causing about $138 billion of damage every year
in sectors such as forestry, agriculture and fisheries. Introduced species often do well in
their new locales in the absence of their natural predators and diseases. Most don't do
much damage, but a small minority take hold and do massive harm. Some are predators
that exploit defenceless native prey species. A famous example is the brown tree snake
(
Boiga irregularis
)
,
a native of the Solomon Islands, New Guinea, northern and eastern
Australia and eastern Indonesia. Introduced to some of the Pacific islands, it has virtu-
ally wiped out many endemic bird species. On Guam alone it is responsible for driving
twelve to fourteen endemic bird species beyond the point of no return. Other introduced
species are powerful competitors, like the American grey squirrel (
Sciurus carolinensis
)
that seems to have pushed out the native red squirrel (
Sciurus vulgaris
) in most parts of
Britain.
P
ollution:
Rachel Carson's seminal book,
Silent Spring,
was instrumental in starting
the green movement by bringing the dangers of pesticides to our attention in 1962. Since
then, pollution of many kinds has become alarmingly widespread. We are only too aware
of gender-bending chemicals in water, and are well informed about atmospheric pollu-
tion such as acid rain from power stations and cancer-causing soot particles. One of the
