Lecture 9
• Genetic Consequences of Invasion
• Low genetic diversity
• May have negative, neutral, or positive (short term) effects
• Low genetic diversity – can limit responses to environmental
stochasticity. Can limit ability of a population to adapt to novel
environments. May contribute to inbreeding.
• In some social insects, low genetic diversity can facilitate much
higher population densities as individual colonies fail to
recognize other independent colonies as distinct preventing
the aggression that maintains lower population density where
the species are native.
• High genetic diversity
• In invasions, usually the product of repeated introductions
• Higher diversity within populations than between them.
This contrast to native range where individual
populations are genetically distinct and most variation
is between populations as opposed to within.
• Brown anole in S. Florida is a good example.
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• Founder effect – gypsy moth in North America (largely a single
introduction) but not raccoons in Germany (multiple independent
introductions).
• Lag times – may be a product of low genetic variability and
maladaptation to novel environment
• Overcome through de novo mutation, gene flow from another
population, or selection on the existing variation within the
population.
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Allee Effects
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Positive density dependent feedback over some portion
of population density.
Allee threshold – point at which population density is
high enough to support positive growth. Below,
population declines to extinction.
Can be a product of enhanced mate finding, cooperative
social behavior like hunting, overthrowing plant
defense or host immune response, attracting
pollinators, saturating predators, etc.
All of these are positive density dependent phenomena
and are particularly important at low population
density.