BIOL488 Lecture Notes - Insular Biogeography, Island, Continental Drift

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7 Feb 2013
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52.4
Wallace: correctly deduced that dramatic differences in flora+fauna were related to depth of
channel separating two areas channel so deep it remained barrier to movement
o established foundations of biogeography: scientific study of patterns of distribution of
populations, species, ecological communities on earth and geological history of area
influences kinds of organisms found there
o Wallace’s Line: line he drew through Malay Archipelago
flora, fauna, and microorganisms (the biota) of world allow us to divide earth into biogeographic
regions: based on taxonomic composition of organisms living in them
o boundaries are set where species change dramatically over short distances
o biotas differ b/c barriers (oceans, mountains) restrict dispersal of animals btwn
o interchanges not been frequent/massive enough to eliminate striking differences that have
resulted from speciation+extinction within each region: most species confined
a species found only within certain regions is endemic to region (ex vascular plants of Madagascar
b/c of water barriers)
biotas of major biogeographic regions are very different from eachother
3 scientific advancements changed biogeography
o acceptance of continental drift theory
Linnaeus believed all organisms created in one place (Paradise) from which they
dispersed, and organisms distributed b/c of massive dispersal
Wegner: continental draft; continents changed position over time
280,000,000 yrs ago, continents united to form single land mass (Pangaea),
then began to separate, and species evolved
o development of phylogenetic taxonomy
biogeographers transform phylogenetic trees into area phylogenies by replacing
names of taxa on a tree with names of places where those taxa live(d)
o development of island biogeography theory to explain why ocean islands have fewer
species that mainland area of same size
2 processes: immigration of new species, extinction of species already present
species pool: list of species on mainland that might possibly colonize
first colonists = new species; as # of species on island increases, they will be
members of species already present; rate of arrival of new species decreases until
reaches 0
first: few species on island, pop’n may grow large; resources divided among more
species; avg pop size of each species will become smaller as number of species
increases; smaller pop = more likely to become extinct, and number of species that
can possibly become extinct increases as species accumulate;
new arrivals may include pathogens or predators, increases extinction
probability therefore rate of extinction increases as # species increases
rate of arrival of new species decreases and extinction race increases, eventually
number of species on island should reach an equilibrium at which at they are both
equal
if more species than equilibrium, extinction should exceed arrivals, species
richness should decline; and vice versa. Thus, eq. is dynamic b/c if either
rate fluctuates, the eq. numbers shifts up or down
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