Lab 10 Island Biogeography - ISLAND BIOGEOGRAPHY Lab 10...

ISLAND BIOGEOGRAPHY
Lab 10
10-1
Reminders!
• Bring memory stick or floppy disc
I. BIOGEOGRAPHY
Biogeography is the study of the spatial and
geographical distribution of organisms. The
central question of biogeography is, “Why do we
find these organisms at this location?” The
answer to this question includes both large scale
answers (the community of species found at a
given location is a function of the species pool
from the larger surrounding region) and small
scale answers (local competition and habitat
conditions determine community composition), as
well as, both historical (the community
composition is a function of species and
conditions that were there previously) and
modern answers (the community composition is
strictly a function of recent processes). When
discussing the composition of a community, we
can analyze it at many taxonomic levels ( e.g. –
genus, family, etc.), not just at the species level.
Biogeography also deals with functional questions
of why certain areas tend to have similar or
different communities. For instance, Figure 1
shows desert habitats from very distant locations
in Asia and North America. Despite very
different geographical locations, they support very
similar communities of organisms. Similarly, the
organisms within those communities may be very
distantly related, but show convergent evolution
toward a similar ecological role. For example, the
recently extinct Tasmanian wolf (Figure 2) was a
predatory animal very similar to North American
and Eurasian wolves. However, it is a marsupial
and is more closely related to kangaroos than
wolves (yep, it’s got a pouch and everything).
Figure 1. Desert grasslands from the Gobi Desert in Asia
and the Chihuahuan desert in New Mexico. Can you tell
which one is which?
Figure 2. The Tasmanian wolf is more closely related to a
kangaroo than a wolf.

Laboratory 10 Island Biogeography
10-2
II. ISLAND BIOGEOGRAPHY
The theory of island biogeography was developed
by Robert MacArthur and Edward O. Wilson in
1967. Many early naturalists, including from
Captain Cook’s voyage, noticed a relationship
between the size of an island and the number of
species it supports ( species richness ), with larger
islands supporting more species. In the
Galapagos Islands, MacArthur and Wilson
documented a similar pattern (Figure 3). This
trend is true not just for plants in the Galapagos,
but also for bird species in Hawaii, bat species in
the Caribbean, amphibians and reptiles in the
West Indies, and others.
Figure 3. The relationship between island size and the
number of plant species. (Image from Campbell and Reece
2005).
In MacArthur and Wilson’s view, the number of
species on an island is a dynamic equilibrium
between immigration and extinction rates. The
balance between the number of new species
arriving and the number of species going extinct
on the island will determine the equilibrium
number of species on the island. This is called a
dynamic equilibrium because the composition of
species on the island might change over time, but