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BIOL 3130 Study Guide - Quiz Guide: Allopatric Speciation, Introgression, Parapatric Speciation


Department
Biology
Course Code
BIOL 3130
Professor
Andrew Mac Dougall
Study Guide
Quiz

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Allopatric speciation:
population splits into two geographically isolated populations.
dissimilar selective pressures; different mutations arise.
Peripatric speciation:
subform of allopatric speciation
very small populations
key issues: founder effects, bottlenecks, genetic drift & random
allelic selection
peripheral populations no gene exchange
inbreeding ‘depression’; outbreeding ‘depression
Parapatric speciation
only partial separation of the zones of two diverging populations
afforded by geography.
individuals may come in contact but reduced offspring fitness
leads to selection of mechanisms that prevent inter-breeding
Sympatric speciation
two or more descendant species from a single ancestral species all
occupying the same geographic location.
mechanism: individuals switching to different microhabitats,
creating fitness differences that become reinforced by sexual
selection
Types of Selection:
Directional: selection against phenotype at one extreme
Stabilizing: Means fitter than extremes
Disruptive: Extremes fitter than mean
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Darwinian Island: Populations never come into contact with source
of individuals (mainland). Fill an ‘empty’ ecological niche. If
isolation persists, species formation results in neo-formation. With
extreme isolation, the ecological space will be filled by speciation.
Fragment Island: Ecological space initially filled by connection to
mainland prior to separation. # of species declines following
fragmentation due to the process of relaxation. If islands become
more isolated, species will arise due to allopatric speciation leading
to “paleo-endemics”
Biological Homogenization: the homogenization of habitat
conditions and species around the globe, as a result of human
activity
ecological: specialization
evolutionary: reverse speciation
Adaptive divergence between populations in response to divergent or
disruptive selection is the cause of ecological speciation
Gene flow between diverging populations becomes reduced, either
indirectly as a by-product of divergent adaptation, or by direct selection
when intermediate genotypes are ecologically less successful
outbreeding depression refers to cases when offspring from
crosses between individuals from different populations have lower
fitness than progeny from crosses between individuals from the
same population.
introgressive hybridization refers to cases where the elimination
of “habitat isolation” (two different habitats becoming
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homogenized into a single habitat) drives reduced diversity or
increased hybridization that may be suboptimal.
introgressive hybridization refers to cases where the elimination
of “geographical isolation” (two different habitats becoming
connected) brings into contact otherwise allopatric species
Two Foundational Principles
1. Species with larger geographical ranges speciate faster (Larger
areas have larger targets for geographically isolating barriers)
2. Loss of area drive up extinction rates, thus reducing the number of
species available for future speciation
Probability of speciation increases when:
Area increases (more opportunity for divergence)
Gene flow strength decreases (gene flow is the main force
opposing population differentiation)
Environmental stochasticity: The larger the area covered by a species'
range, the less chance that range will suffer permanent or temporary
obliteration. Again, a larger area diminishes extinction rates.
Centrifugal speciation: large populations speed up speciation, beginning
with geographical separation of sister populations. After separation, the
larger isolatesnot the smaller ones. The small ones remain as
evolutionary relicts.
Deterministic extinctions: the loss of all areas in which a species can
sustain its demographics.
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