BIOL 230- Week 3 Learning Outcomes:
Lecture 5: Island Biogeography:
Why do large areas have more species than small areas?
1.Describe (verbally, mathematically) a species-area relationship (SAR)
Increase in size of area = Increase in species number (strong linear relationship)
Larger Caribbean islands have more species
Equation of a species area relationship (SAR): S= zA+c
o S-species richness, A-area, z-slope of line, c-y intercept of line
o SARs can be plotted in either linear or log-log space, but easier to see patterns in log-log
2.Expalin which processes create SARs
Why large island more species?
o Sampling effect:
Larger area- More individuals- More species
Even sampling effects can result in nonlinear (power) relationships
o Habitat effect:
Larger area- More habitats- More species
o Class activity 1: Why was the effect of area stronger for Scenario 2 than 1?
2 things limited the # of species in small areas in scenario 2: low numbers of individuals
and few habitat types
Only 1 of these limited species in scenario 1 (individuals)- more habitat types
o Class activity 1: Did the nested and between-region SARs differ in Scenario 2?
Nested: different sized areas within the same region; Between-region: different sized
areas in different regions
It did not differ- no difference in # of species between small and large islands when we
sampled the same area (scenario 2)
Still restrained area and that constrained the number of individuals and habitats
Overview: Island: The number of species the region can support in terms of: Resources, Individuals,
o A stock and flux model for island species richness
Rate that species enter island: speciation, immigration
Island: Number of species the island can support in terms of: resources,
o Rate that species leave island: extinction, emigration
o Can simplify the rates by ignoring speciation and emigration
Why will we not be considering speciation and emigration?
Speciation rate increase with region area, BUT only on large islands isolated for
long periods of time
So area effects on speciation are not relevant for smaller areas and shorter time
Emigration can be ignored- although theoretically possible, no species is lost
because the last individual of the species left the region or island!
How do immigration and extinction affect the species richness in a region?
o What we learned: As the number of species increases on the island, extinction rates go up and
immigration rates go down. 3.Use Island Biogeography Theory to explain effects of island properties on equilibrium species richness
Theory of Island Biogeography:
o Immigration only affects species richness if the species is not already represented, which
becomes increasingly unlikely as the region fills up with species
o Extinction becomes more likely as region filled with species, as resources become scarce
o Reach equilibrium- where every loss, you gain
4.Explain what a “dynamic equilibrium” means
This is a dynamic equilibrium:
Dynamic: continual change in the identity of the species
Equilibrium: when the region has more or less than the Seq (Species equilibrium)
value, there is a tendency to return to it.
o How could island biogeography theory explain SAR?
Declining population cannot be rescued on small islands
Rescue effect: populations in undisturbed areas recolonized locally extinct
Smaller islands could have lower immigration rates, higher extinction rates
What is the affect of area on immigration rate?
o A-larger areas receive more seed and other propagules
o D-larger areas are more detectable by colonists
o B and C are post-immigration processes
Three explanations for species-area relationships
o 1.Sampling effects- more individuals, more species
o 2.Habitat diversity- more habitats, more species
o 3.Island biogeography- high immigration and low extinction, more species
5.Explain what processes are important for a within-region (nested) versus between region SAR
Nested and between-region SARs did not differ when we consider just sampling and habitat effects
The Theory of Island Biogeography predicts differences in immigration and extinction of species
BETWEEN regions, not WITHIN regions
Lecture 6: Life history strategies:
Life history continuums
Life cycle evolution
1.Understand how reproductive strategies can be cl