The Geography of Evolution – Chapter 6
Biogeography
•The study of the geographic distributions of organisms
Biogeographic evidence for evolution
•Darwin noticed that the distribution of organisms did not make sense under the hypothesis of special creation and supported his theory of evolution
–Similarity of organisms not related to climate
–Barriers are related to differences between organisms of different regions
–Inhabitants of the same continent or sea are related even though species differ from place to place
Similarity of organisms not entirely related to climate
•There are similar climates on different continents, yet organisms in the same habitat are unrelated
Barriers are related to differences between organisms from different regions
•Marine species on east and west coast of South America are different
Inhabitants of the same continent or sea are related even though species differ from place to place
•Aquatic rodents of South America related to terrestrial rodents of South America, not aquatic rodents of North America
Biogeography
•All of these show evidence of common ancestry and “descent with modification”
•Species had a single region of origin, as evidenced in island species
Biogeographic realms
•Recognize that the taxonomic composition of an area is more uniform in areas than between the areas
•Biogeographic realms are a result of Earths’ history
Biogeographic realms can be separated into provinces
Higher taxa may have disjunct distributions
Disjunct ratite distribution
Historical biogeography
•Geographic distribution can best be explained by historical circumstances
–Extinction patterns
–Dispersal patterns
–Vicariance (separation of populations due to barriers arising from changes in geology, climate or habitat)
Phylogenetic analysis
•Extension of parsimony in reconstructing geographic distribution of ancestors on the distribution of living taxa
•Ronquist’s Dispersal-Variance Hypothesis (DIVA)
–Assume vicariance is the null hypothesis
–Each time extinction or dispersal occurs, extract a cost
–The hypothesis that has the lowest cost is the most likely explanation for current patterns
•Best model would explain pattern for more than one taxa
Dispersal model
Simple vicariance
Vicariance with extinction
Some terms
•Allochthonous – taxa that originated elsewhere
•Autochthonous – taxa that evolved within the region
Historical biogeography in Hawaii
Historical biogeography in Madagascar
Break up of Gondanaland in Cretaceaous
History of breakup of Godwanaland
Evidence for Panther chameleon dispersal
Cichlids in Africa
Ratites
Galliformes and Anseriformes
Passerines
Phylogeography
•Description and analysis of processes that govern the geographic distribution of lineages of genes, within populations and among closely related species
Habitats during glaciation
Gene tree
Inferred pattern of re-colonization
Human origins
•Multiregional hypothesis
Replacement hypothesis
Modern Homo sapiens
Ecological biogeography
•Geographic distribution can best be explained by ecological factors currently operating
Island biogeography
Island biogeography
•The equilibrium number of species S on an island reflects a balance between immigration and extinction
•“Equilibrium” applies only to species richness, not species composition
Island biogeography
•Immigration rate (I) determined by isolation of island
–further islands have lower immigration rates
Island biogeography
•Extinction rate (E) determined by size of island
–the smaller the island = the smaller the population = greater chance of extinction
Island biogeography
•Equilibrium richness is where immigration rate equals extinction rate
Island biogeography theory predictions
Island size
Community structure
•Only two honeyeaters on each mountain range suggests community constraints on biogeography
Community convergence
•Convergence of communities
•Niche equilibrium
Ecological history