Geography Reference
In-Depth Information
Aliens and biosecurity
Humans are also agents of dispersal and distribution of species. The
growth of long-distance transport has effectively bridged former
barriers to movement for species. The deliberate introduction of
wild animals from one region to another has often had unintended
consequences on the ecosystem. Rabbits were introduced to Aus-
tralia in 1787 and 1791 and, lacking predators, were able to grow
their populations at enormous rates, damaging the native vegeta-
tion cover and becoming pests. Foxes were then introduced as the
natural predator to the rabbit but instead preferred to prey on
native marsupials and birds, devastating their populations. The grey
squirrel introduced from North America to Europe is currently
causing the displacement of the native red squirrel in Britain. Many
species of plants and animals (e.g. rats) have been accidentally trans-
ported in vehicles, ships and planes and become alien invaders,
sometimes spreading disease or driving other species to extinction.
Deliberate and accidental introductions of species, which act as
weed species without their natural controls of predators, alter local
balances. Being careful to restrict the number of unwanted alien
introductions is therefore an important activity at airports, ports
and other borders as part of biosecurity. Ships, aircraft and mail are
searched and sanitised as a matter of routine by many countries.
Another routine procedure requires ships to empty water-ballast
tanks mid-voyage.
Agriculture
Agriculture now dominates the landscape across many areas of the
world. The area of agriculture is expected to enlarge by as much as
50 per cent as the world's population grows. The agricultural
process will also consume more water which may restrict water
availability for other ecosystems. Agricultural systems are ecosys-
tems with managed inputs and outputs of energy and nutrients
with controlled species diversity. Energy flows occur along simple
routes. A higher proportion of the Sun's energy is made available
to crop plants and then passed on more directly to humans or indi-
rectly through livestock. This also means that a higher proportion
of the primary production is exported from the system as the
