Geography Reference
In-Depth Information
Island biogeography
The study of isolated islands has yielded much useful understanding
about how biogeographical processes operate. Islands have clear
boundaries and their isolation and lack of many external factors
simplify the system and make it easier to understand. Classic island
biogeography theory examines the balances between rates of immi-
gration of new species to an island and rates of extinction on that
island. If immigration rates are high and extinction rates are low
then the island should be rich in species. The species richness
should be related to the size of the island and how far it is away
from another land mass. If an island is a short distance from a major
land mass then there will be more opportunities for new species to
arrive. Larger islands are more likely to have a wider variety of
habitats and so might be able to support a larger range of species.
The rate of extinction of species inhabiting a new island starts off
low, since competition for resources would be low. As the number
of species increases then the pressure on resources also increases and
so the rate of extinction rises over time. If an island is created by
severance from the main continent then the island might start off
with high species richness. However, as the island has restricted
resources then extinction rates will increase at first resulting in a
decline of species richness.
Island biogeography theory has also been used to help under-
stand best management practice for conservation. For example,
there have been questions about whether it is better to conserve
one large area within a landscape or conserve several smaller areas.
One large area might be more species rich and work well for con-
servation, particularly if there are large scale migratory routes
through that landscape. On the other hand, while lots of small
patches might mean there is less species richness within those
patches, the chance of complete loss of that ecosystem (and extinc-
tion of species) is reduced because there are lots of patches with
replicated ecosystems.
THE BIOMES
Biomes are global areas containing major terrestrial vegetation
communities with similarities between the dominant plants and
