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Ecological Impacts of Invasive Species
Marieke and Ann
Genetic Level
• Defined as alterations to the native gene pool
through hybridization and introgression
– Easy definition is backcrossing, producing gene
flow between the native and invasive
New Zealand grey duck
Australian black duck
Hawaiian duck
Individual Level
• Defined as alterations to the fitness or traits of
individuals, including changes in morphology
or behavior
Population Level
• Competition: non-natives
outcompete natives
• Predation: most discussed because of devastating
impacts on evolutionarily naïve natives
• Physical: physical attributes
of the invader
Community Level
• Mass extinctions: evolutionary isolated systems
receive a novel predator or herbivore
• Community alterations:
whole community changes,
especially on islands
Ecosystem Level
• Altering the flow of materials through the
ecosystem or the disturbance regime
Landscape, Regional and Global Level
• Endemic species most affected, naïve
• Homogenization: the idea that the world will
eventually look the same across all continents
• Think of some examples not in the chapter
and classify their impact (genetic, individual,
population, community, ecosystem, global).
• Do you agree with the following statement:
“…impacts will generally only result from species
that have moved through all previous stages.”
• What is the role of humans in the struggle to
maintain “genetically pure” native
populations? How do we stop hybridization?
• In the Species Survival Plan for tuataras three
options for recovery are listed:
– Do nothing
– Eradicate the kiore
– Captive breeding program for tuataras, with
• Which option(s) would you choose?
• Which, if any, of the different levels discussed
are the most “insidious”?
– (The authors believe the genetic level impacts are most destructive.)
Figure 9.3 Fecundity (fruits/plant) of Arabis fecunda individuals
through time, in control and treatment plots. The treatment was
the removal of spotted knapweed (Centaurea maculosa), an
invasive plant in the northwestern USA. Although fecundity was
influenced by annual climatic events (i.e. rainfall), the removal of
the invasive consistently resulted in higher rates of reproduction
for the rare native. From Lesica and Shelly 1996.
Figure 9.4b Size-class frequency distribution (SVL =
snout-to-vent length) for tuatara on kiore-free (uninvaded) and kiore-inhabited (invaded) islands. The
distributions differ significantly, with a noticeable
absence of small juvenile tuatara on invaded islands.
Figure 9.5 Histograms of total
ant species richness in sites with
and without the imported red
fire ant (Solenopsis invicta).
Figure 9.6 Histograms of native
ant abundance over sites with
and without the imported red
fire ant.