Geography Reference
In-Depth Information
Migration and trade
Human beings are a species on the move. We migrate (see Chapter 12). We travel for business and
leisure. We engage in global trade and commerce (see Chapter 15). And in the process we sometimes
purposefully or inadvertently transfer a particular species from its current home to a part of the world
where it was previously unknown, possibly with negative environmental consequences. Following
are two examples.
Rabbits were unknown in Australia until 1859, when a dozen or so were purposefully introduced to
serve as a source of food. Lacking natural predators in their new homeland, their numbers went bal-
listic, reaching about a billion within a century. This could rank as the ultimate bunny joke, except
that sheep are important to the Australian economy, and five rabbits eat about as much grass as one
sheep. Poisoning campaigns have subsequently killed off literally hundreds of millions of rabbits, but
people now fret about the impact of those substances on local food chains (a concept discussed in the
next section.)
In 1988, an East European freighter in the Great Lakes dumped some ballast water (whose sole pur-
pose is to add weight to a ship that would otherwise bob like a cork), and with it probably introduced
the zebra mussel to North America. This diminutive critter with cute little stripes is native to the
Black and Caspian Seas, where certain duck species and crayfish keep its numbers in check. Lacking
a large predator population in the Great Lakes — plus the tendency of adult female zebras mussels to
produce more than 30,000 eggs per year — the population soared at a rate that would make an Aus-
tralian rabbit swoon. The mussels attach to hard surfaces, and in the process have caked and stopped
up water intake vents of waste and industrial treatment plants.
Focusing on food chains
While one may decry negative environmental impacts on ethical or scenic grounds, the repercussions
for human well-being is perhaps of paramount importance. Food chains provide an excellent example
of how negative impacts may come back to haunt humans big time. No, not
fast
food chains that
provide hamburgers, tacos, fried chicken, pizza, or other staple foodstuffs; but instead the food chains
that involve consuming and passing along injurious substances in ways that prove ultimately harmful
or fatal to humans and animals.
