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ALIEN INVASION
INVASION ECOLOGY…CURIOUSER &
CURIOUSER
vocabulary
indigenous = native to a particular place
biogeographical = the branch of biology
that studies the geographical
distribution of organisms
The Enemy Release Hypothesis (ERH)
 Relates the success of non-indigenous species (NIS)
to reduced control by enemies



Pathogens
Parasites
Predators
 Studies are split
 Biogeographical analyses show a reduction in the diversity of
enemies in the introduced range compared with the native
range
 Community studies imply no significant enemy differences
between natives and invasives
 Too simple to describe processes at work?
Evolution of Increased Competitive Ability hypothesis
(EICA)
 Blossey & Nötzold (1995)
 Observations
 Usually a lag period between time of introduction & point at
which it is considered invasive
 Invasive plants seem to be more virulent in habitats into which
they have been introduced (as compared with their native
habitats)
 Presumed a sort of naturalization through
modification
 Predicts that much of the invasive potential of an
invasive species is derived from its ability to evolve to
reallocate its resources
Invasion model
 Plasticity and adaptive evolution can lead to
Species frequency
greater invasiveness
Introduced
Local
adaptation
Phenotypic
plasticity
Naturalized
Lag
Invasive
Sexton et al. 2002. Ecological Applications 12:1652-1660.