Transcript ETIB PowerPoint

Regional diversity
• What factors operating at regional scales
account for local patterns of species diversity?
– Dispersal
• Range expansion/contraction
• Movement into new areas
– Speciation
• Vicariance, ecological speciation, speciation by
polyploidy, etc.
– Extinction
The Equilibrium Theory of
Island Biogeography (ETIB)
• Robert H. MacArthur and E. O.
Wilson (1963)
• What is an island?
• What is biogeography?
• What is dispersal?
What is an island?
• Ecological island: habitat surrounded by an
inhospitable matrix
– Oceanic islands
• surrounded by saltwater
– Continental islands
• e.g. patches of habitat
– Other islands
• “sky islands” = montane habitats surrounded by
desert or forest
• Lakes and ponds surrounded by terrestrial habitat
• Rivers and streams, separated by dry drainage
divides
Alexander von Humboldt (1769-1859)
Russian naturalist &
explorer
Father of biogeography
1799-1804 travelled
throughout Latin and S.
America
Documented several
key biogeographic
patterns
The species-area
relationship (SAR)
The SAR is one of the
“laws” of ecology.
What could cause this
pattern?
Discuss.
General interacting explanations
• Habitat diversity hypothesis
• The likelihood of encountering new habitat types and
thus new niches for different species increases as area
increases.
• Dispersal hypothesis
• Large areas are likely to receive more colonists than
small areas.
• Area-Extinction hypothesis
• The population sizes of species are greater in large
areas. Thus, fewer species go extinct than in small areas
where there are more rare species.
ETIB immigration and extinction
• How are I and E modeled in the ETIB?
ETIB immigration and extinction
• How are I and E modeled in the ETIB?
Immigration
Rate
I
P
No. species on island (S)
ETIB immigration and extinction
• How are I and E modeled in the ETIB?
Immigration
Rate
I
P
No. species on island (S)
P = total no. of species in the regional species pool
ETIB immigration and extinction
• How are I and E modeled in the ETIB?
Immigration
Extinction
E
Rate
Rate
I
P
P
No. species on island (S)
No. species on island (S)
P = total no. of species in the regional species pool
ETIB: equilibrium species number
• What is the equilibrium species richness for an island?
ETIB: equilibrium species number
• What is the equilibrium species richness for an island?
• This is produced by the interaction of the I
and E curves, determine equilibrium
number species (S’)
I
Rate
E
P
S’
No. species on island (S)
P = total no. of species in the regional species pool
ETIB: theory
on area and
isolation
• Large islands should hold
larger populations than
small islands, so large
islands should have
reduced extinction rates.
ETIB SUMMARY
• Lowest diversity: small-distant islands
• Intermediate diversity: small-near and largedistant islands
• Highest diversity: large-near islands
How does island isolation affect
extinction and immigration?
• Isolation should also
affect how frequently
declining populations
are “rescued” from
extinction.
In
Rate
• The distance of an
island from the
mainland (a source of
colonists) should affect
the immigration rate
and thus, species
diversity.
E
If
P
Sf
Sn
No. species on island (S)
“The rescue effect”
How does island size affect
extinction and immigration?
I
Es
El
Rate
• Extinction rates on
small islands would be
higher because small
islands have smaller
populations than large
islands.
P
Ss Sl
No. species on island (S)
• Larger islands may
accumulate more
species by chance just
because they are larger
targets.
“The target effect”
Extending area and distance
effects in the ETIB
Immigration (I)
Area
Distance
Target
Effect
ETIB
ETIB
Rescue
Effect
Extinction
(E)
Rate
In
Es
El
If
P
Ssf Ssn Sln
Log no. species
Ultimately, however, the ETIB
predicts the SAR
Sln
Ssf
Slf
Ssn
Island area (A)
Slf
No. species on island (S)
… even without target and rescue effects.
Species turnover
• Definition: change in species composition
from one community to another through
time
Island biogeography theory makes 2
general predictions:
1. Species diversity is affected by size and
isolation
2. Community composition is dynamic
Tests of island biogeography theory
• Dan Simberloff
and E.O. Wilson’s
test on mangrove
islands in the
Florida Keys
• Jared Diamond’s
test on
California’s
Channel Islands
Dan Simberloff
(1942-present),
University of
Tennessee
Jared Diamond (1937-present)
University of California at Los Angeles
Guns, Germs, and Steel: The Fate of Human Societies
Collapse: How Societies Choose to Fail or Succeed
Tests of isolation determining immigration
and richness:
• Insects and spiders in the
Florida Keys
Results:
Tests of turnover and
equilibrium prediction:
Results:
Extinctions were
balanced by
immigration despite
turnover of species
Assumptions of island
biogeography theory?
No speciation
Equilibrium dynamics prevail
Problems?
Both are unrealistic
Near, large islands may have the same number
of species or fewer species than small, distant
islands.
Non-equilibrium dynamics
Should we always expect an equilibrium or
steady balance between immigration and
extinction?
Non-equilibrium in this context means that the
slopes of the colonization-extinction curves for
an island varies over time. Thus, where the two
lines cross varies and the island diversity varies.