Transcript Island Biogeography: Species Richness

Island Biogeography
• Equilibrium Theory
• Explanation of community structure as a
function of size and distance from species
pool
• Dispersal
• Geographic Isolation
• Extinction
• Makes it applicable to more than true
islands
Island Biogeography
• MacArthur and Wilson used past island
studies to develop the theory
• Species-area relationships
• Species turnover
• Species Isolation
Species-Area Relationship and Size
Rare Species and Extinction
Applies to Distance
Isolation and Species Area
Species Isolation
Species Isolation
Species Turnover
Species Turnover
Species Turnover
Equilibrium Theory of Island Biogeography
Criticisms of Island Biogeography
• Interspecific differences and species
interactions
– Assumed immigration, extinction, and turnover
as stochastic
– Species richness not composition
• Interdependence of immigration and
extinction
– Treated as independent processes
– Does not account for recruitment of new
individuals already on island
Criticisms of Island Biogeography
• Biogeographically meaningful measures of
isolation
– Sometimes difficult to identify source without
studying systematics
– Composition question
• Biogeographically meaningful measures of
island size
– Spatial heterogeneity
– Ecological and biogeographical history
Criticisms of Island Biogeography
• Importance of speciation
– If species are derived on island, then model is
violated
– Speciation probably only important on large,
isolated islands in terms of number of species
• Disturbance (ecological and geological time
scales)
– Would prevent equilibrium
Tests of Island Biogeography
Estimates of turnover on southern California Channel Islands
Krakatau Revisited – Colonization Curves
Krakatau Revisited – I/E rates
Krakatau Revisited – I/E rates
Simberloff and Wilson (1970) Experiment
Krakatoa Revisited – Plant Colonization
Succession had to
proceed to allow
animal colonization
Accounting for Succession/Recruitment
• How does succession
alter likelihood that
immigrants will
survive and
reproduce?
• F = failure rate
(species failing to est.
breeding population
• C=I–F
• C decreases over time
Disturbance Events
• How to account for
disturbance effects?
• Disturbanes at same
temporal scale as
island I and E might
prevent equilibrium
• Shorter time scale
(fires, drought…..)
probably only slow
process
Possible Effects of Speciation
Effect of Area
Effect of Distance
“Island” Applications of Island Biogeography
• Freshwater Lakes
• North American lakes (Post-Pleistocene)
relied on connections to other waters,
including streams and rivers, for
colonization
• Not near saturation
• Example – Great Lakes; large but not many
species; lotic sources depauparate
“Island” Applications of Island Biogeography
• African lakes – much older; high diversity
from speciation through adaptive radiation
• North American lakes, including Great
Lakes, show evidence of same but not much
time has passed
Species-Area
Relationships
Species-Area Relationship in Rivers
• Greater diversity in N.
Amer. rivers
• N. Amer. rivers
generally have N-S flow
• Would allow dispersal
in advance of glaciers