Understanding Invasive Species

Invasive species have certain traits that facilitate their successful establishment and impact in new environments.
Important points of discussion include:
- Characteristics that invasive species possess.
- Characteristics of communities that are more susceptible to invasion.

Definition: An exotic species is one that has been introduced, either accidentally or deliberately, by human actions beyond its natural geographical range.
Example: House sparrow.

Definition: An invasive species is defined as an alien species whose introduction results or is likely to result in economic or environmental harm or harm to human health.
IUCN Definition: Animals, plants, or other organisms introduced by humans into places outside their natural range of distribution, where they become established and disperse, generating a negative impact on the local ecosystem and species.

Factors affecting the success of introduced species include:
- Chance events (e.g., the failed introduction of starlings in New York).
- Ability of the species to reproduce and find mates at low densities.
- Vulnerability to climatic variation and photoperiod.
- Impact of predators or diseases.
Note: There is no single answer to why most introductions fail.

Successful introductions can have significant negative impacts on ecosystems.
- Example: In Guam, around the 1980s, four native bird species became extinct and ten were endangered.
Investigations into the decline of bird populations revealed that an invasive species, the Brown Tree Snake, was a significant factor.

The Brown Tree Snake (Boiga irregularis), native to New Guinea, was introduced to Guam in the 1950s via military shipping cargo.
Consequences of the introduction:
- Loss of 9 out of 18 native bird species.
- Loss of 6 out of 12 native lizard species.

The snake's range expanded by approximately 1.6 km (1 mile) per year.
By 1984, all native bird species were extinct in the last area where they were found.
- The Bridled white-eye was last seen in 1983 and is now extinct.
- The Rufous fantail and Guam flycatcher are also extinct.
- The Guam kingfisher and Guam rail are extinct in the wild but are undergoing captive breeding programs.
- The Mariana fruit dove is extirpated on Guam but survives on other islands.

Burmese pythons, popular as pets, have been imported in thousands to the US, with many likely released into the wild deliberately.
Established in the Everglades around 1979, estimates of their population currently range from 50,000 to 180,000 snakes.

Pythons consume a wide range of prey, resulting in decreases of around 99% in many native mammal populations.

Asian carp, a group of 7-8 species, were introduced from China/Asia to clean up fishery ponds and subsequently escaped into wild waters.
Highly invasive, they attain very dense populations, disrupting ecosystems significantly.

They primarily feed on native mussels and snails, some of which are endangered, and alter aquatic food webs by affecting plant and invertebrate communities.
Large adult Asian carp can produce millions of eggs, contributing to rapid population increases.

Strategies to control their spread include constructing electric barriers in the Chicago Waterways to prevent their movement towards the Great Lakes.

Observation of snakehead fish in Georgia, an aggressive invasive species capable of surviving on land and reaching quick sexual maturity with high fecundity.
Examples of other invasive species include: Kudzu, Argentine Tegu, and Cane Toads.

Key Terms:
- Invasive species
- Exotic species
Notable Case Studies:
- Brown Tree Snake
- Pythons in the Everglades
- Snakeheads
- Asian Carp
Understanding invasive species is essential for conservation strategies and ecological management in various environments.