Testing Your Comprehension
Biodiversity has no single definition. At the species level, it refers to both the number of
different species present in an area and to the evenness or relative abundance of those species. At the
genetic level, it refers to the genetic variety within a single species. At the ecosystem level, it refers to
the number and variety of ecosystems in an area. The concept may be applied at the levels of the
community, the habitat, or the landscape as well.
Habitat alteration, invasive species, pollution, overexploitation, and climate change are all causes
of biodiversity loss. Examples, in the order of the factors just mentioned, are hydroelectric dams altering
stream habitat, zebra mussels in the Great Lakes, air pollution killing forest trees, Siberian tigers being
hunted to near extinction, and climate change affecting the cloudforest fauna in Monteverde.
The zebra mussel, a small, striped mollusc, has spread rapidly through eastern North American
waterways, fouling ship motors, pumps, docks, etc. Feral pigs in Hawaii alter the habitat for mosquitoes,
aiding the spread of the invasive mosquito species
which spreads avian malaria
and avian pox diseases amongst the native bird populations. Humans are an invasive species in many
parts of the world. We’ve brought with us many agricultural species, as well as many weeds, some of
which have naturalized in their new habitats, thus altering the local ecological balance.
Processes provided by ecosystems, such as air and water purification, are called
. Besides those just mentioned, ecosystems also provide food, fuel, and fiber; detoxify and
decompose waste; and stabilize and moderate Earth’s climate.