Name: Khloe’ Couey_____________
Island Biogeography Inquiry Lab
Read the introduction below:
Biogeography explores global patterns in species diversity.
Two major factors that influence the number of
species that are found in a given place are the amount of available habitat and distance among communities.
The Equilibrium Theory of Island Biogeography
explores these concepts by focusing on diversity on islands.
You will use a simulation to investigate and explain this theory.
One of the first global patterns of diversity that early scientists observed was the relationship between area/size
and the number of species that a space holds.
This relationship was easy to describe on islands where species
richness of multiple groups of animals or plants (taxa) had been described.
For example, Figure 1 demonstrates this
. For example, Cuba is the largest
island in the Caribbean, and Redonda is one of the
smallest. If you look at the number of species found
on each island (y-axis), Cuba has far more species
than Saba does.
Ecologists noted that species
richness did not just increase with size; it tended to
increase at a regular rate.
In general, we find that
an area that is 10 times larger has about twice as
(Note this relationship appears
linear in the figure due to the use of log scales on
While studying patterns of species richness on islands, two
ecologists, Robert H. MacArthur and Edward O. Wilson (a super
famous ecology dude!),
noted some exceptions to the rule. For
example, some large islands had fewer species than expected due
to their size, while some small islands tended to be more species-
rich than expected.
To explain these global patterns they
proposed the Equilibrium Theory of Island Biogeography.
focuses on how size and distance from a "mainland", or source of
species, influences island richness.
To understand the Island
Theory of Biogeography, let's first consider Figure 2 to the right.
Imagine there are two islands
located off the coast of the
mainland. Although the two islands are about the same size, the
second island is located much farther away than the first island. If you are a bird that lives on the mainland,
which island are you most likely to end up on? The answer is generally the first island.
This means immigration
(or colonization) is influenced by the distance of an island from the mainland (a source of colonists). Therefore,
islands that are closer to the mainland are more likely to receive immigrants than islands that are further away.
Once a species manages to reach and colonize an island, the rate of extinction is largely influenced by the size of
the island. This is because smaller islands tend to hold smaller populations (which are more likely to experience
extinction due to chance negative effects like genetic drift!).
Larger habitat size reduces the probability of
of the colonized species due to chance events.
Smaller islands are also likely to hold fewer
populations in general because they have less resources and less diversity of resources.