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What are invasive species?
Can you think of any examples?
Invasive species
• Non-native, introduced species (plants or
animals) that has a negative impact on the
habitats it invades.
What traits do you think would help a
species become a successful invader?
Good dispersers
Not picky eaters
 Able to change form to
tolerate varying conditions
Close
association
with humans
Rapid reproduction
The environment itself can also
play a role in invasion
• The amount of available unused resources
• Disturbed habitats (fire, human use)
• Absence of predators or herbivores that can eat the
invasive
Human disturbance:
Herbivore present:
Herbivore absent:
How bad can it be?
• Outcompete native species for limited
resources (space, food, etc.)
• May directly reduce population size of
natives by predation or herbivory
• If the invasive species is toxic it may kill off
native predators or herbivores that try to
eat it
• May change function of ecosystems (fire
regimes, nutrient cycling)
What can we do to control or
remove invasive species?
• There have been numerous different
methods used to control invasive species.
Chemical control
• Herbicides and pesticides are used to kill
off invasives. Occasionally these
chemicals are species specific (e.g.
lampricides).
Reproductive interference
• Some methods try to disrupt the reproductive cycle by
releasing sterilized males into the population.
• Use of synthetic pheromones can also interfere with
reproduction
Biological control
• Releasing predators or herbivores to eat
the invasive species
• Releasing a pathogen into the invasive
species population
Herbivore present:
Herbivore absent:
Barriers
• Construction of
physical or nonphysical barriers
(e.g. electric
barriers) that block
the spread of
invasive species
Physical removal
• Manually removing the invasive species from
the area (hunting, pulling up plants, trapping,
etc…)
Example: Cane toad
•
•
•
•
Introduced to Australia, quickly became invasive
Eats just about anything
Very high reproductive rate
Toxic
Cane toad control
• Most attempts at control have focused on physical
removal
• Future efforts are looking at using an alarm pheromone,
lung parasite, and a natural predator to control the toad
Example: Cactoblastis moth
• Caterpillars feed on prickly
pear cactus
Cactoblastis moth
N
I
N
I
N
C
N = native
I = invasive
C = control
Cactoblastis moth
• Cactoblastis is a biocontrol in Australia, but it
needs to be “biocontrolled” in North America,
where it is invasive.
• Some research is exploring
the possibility of introducing a
parasitic wasp from South
America that lays eggs in the
Cactoblastis caterpillars.
• The wasp larvae eat the
caterpillar from the inside out.
Example: Zebra mussels
• Since they were first sighted in Lake Erie in
1986, zebra mussels have spread to 30 states.
• http://nationalatlas.gov/dynamic/dyn_zm.html#