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Invasive Species. Also the topic of our new course. An exciting topic which may be the most important conservation issue today. So, what is an invasive species?. Monk Parakeet colony near Chicago, Illinois. Can you find Guam and New Guinea on a map of the world? .

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Invasive Species

Also the topic of our new course

An exciting topic which may be the most important conservation issue today

so what is an invasive species
So, what is an invasive species?

Monk Parakeet colony nearChicago, Illinois


Can you find Guam and New Guineaon a map of the world?

Brown Tree Snake introduced to Guam, but they are native to New Guinea

"Exotic," "alien," "introduced," non-indigenous," and "non-native" are all synonyms for plant or animal species that are intentionally or unintentionally introduced into an area outside of their natural range.


New Guinea

New Guinea


Factors Determining the Success of an Exotic Species

1. Suitability of Habitat and Ecological Niche

English Sparrow


2. Adequacy of the “introduction unit”

a. Health

b. Behavior- including social aspects

c. Simple numbers

3. Degree of escape from diseases, parasites and predators

4. Degree of escape from competitors


Mechanisms of Introduction

1. Intentional

European Rabbits in Australia


Rabbit Impacts on Native Wildlife

1. Direct competition for food

2. Selective grazing changes ecosystem composition

3. Evicted various species from their burrows- e.g. bilby, hare-wallaby

4. A colony of rabbits will support a high number of predators (e.g. feral cats and introduced foxes) which will shift to other, more easily obtained, native prey

5. Native wildlife killed by poisons and traps set for rabbits


6. Shooters, culling rabbits, also culled native species for the pelt trade.

7. Bounties paid for wombats, why?

8. Harm to vegetation during drought- digging of roots and ringing


Original distribution

Present distribution of Rusty Crayfishrange intentionally expanded by anglers

Rusty crayfish (Orconectes rusticus) are native to streams in the Ohio, Kentucky and Tennessee region. Spread by anglers who use them as bait, rusty crayfish are prolific and can severely reduce lake and stream vegetation, depriving native fish and their prey of cover and food. They also reduce native crayfish populations


3. Natural Invaders

Cattle Egret- native to Africa, first crossed to South America then into the United States in the 1940’s


Determinants of Impact

1. Ecological distinctiveness- highly successful invaders are usually different in structure, physiology or behavior from native forms

Keystone Exotics

Kudzu, a keystone exotic species infestation in Georgia. Keystone species are those, that if lost, would precipitate an extinction cascade or vortex


Zebra Mussel- introduced into the Great Lakes in the ballast of oceanic ships

Determinants for Impact

2. Potential for competitive exclusion

Zebra Musses attached to the shell of a native mussel in the Ohio River


One of the more drastic impacts of zebra mussels are their influence in causing the near extinction of native American unionid clams in Lake St. Clair

  • Also found to be the case for the western basin of Lake Erie
  • Zebra mussels will attach and build colonies on native species of clams, hindering movement and overall fitness

Zebra mussels attached to a native clam found within the Great Lakes region

interesting zebra mussel attachments
Interesting Zebra Mussel attachments
  • Sometimes they even attach to one another
  • Zebra mussels tend to colonize on just about anything, including native clams, boats, plants, and slow moving animals
  • Zebra mussels have also been known to attach to trash that can be found in water bodies

Terrible waste of a good beer can

Zebra mussels attached to a crayfish (top) and a snapping turtle (bottom)

Since zebra mussels attach to water intakes, surrounding areas could go for days without any water
  • Companies that use water to power their plants can have trouble keeping them up and running
  • A number of plants in the Great Lakes regions are having trouble keeping the zebra mussels out of their water intake pipes

Zebra mussels encrusted inside water pipes


Chestnut Blight

3. Potential for disease transmission

Fungi accidently introduced on Chinese Chestnut trees imported to the United States, the map documents the timing of the spread


Cutthroat Trout

Rainbow Trout

4. Potential for genetic swamping

Rainbow trout introduced for anglers, readily hybridizes with native species such as cutthroat trout.


Dealing with Detrimental Exotics

1. Prevention of entry

2. Control of spread

3. Creation of pristine areas

4. Local eradication

5. Protection of individuals

6. General population reduction