Invasive Species
Invasive species are a major topic in ecology because they connect population growth, species interactions, community structure, and biodiversity. The key is distinguishing a non-native species from a species that becomes invasive.
Invasive Species
What Is an Invasive Species?
An invasive species is a non-native species that establishes and spreads in a new environment and causes ecological, economic, or other harm. The key idea is not simply that the species came from somewhere else. A non-native species becomes invasive when its spread produces harmful effects.
Species can be moved intentionally or accidentally through transportation, trade, agriculture, gardening, pets, ballast water, and other human activities. Once introduced, some species fail to survive, some persist without major effects, and a smaller subset spreads aggressively and causes harm.
Non-native does not automatically mean invasive. “Invasive” describes a non-native species that establishes, spreads, and causes significant harm.
Native, Non-Native, and Invasive
Historically established
A species that occurs naturally in a region without having been introduced there by humans.
Introduced outside its historical range
A species occurring in an area where it did not historically occur, often because of human activity.
Non-native + harmful spread
A non-native species that establishes, spreads, and produces significant negative effects.
Why Can Invasive Species Become Successful?
Introduced species encounter different environmental conditions and species interactions in their new range. Some may have traits that allow them to reproduce quickly, use resources effectively, tolerate a broad range of conditions, or exploit resources that native organisms are not using efficiently.
In some cases, introduced species may encounter fewer predators, parasites, or diseases than they experience in their native range. This can reduce biological controls on their population growth. However, there is no single trait that explains every invasion.
How Do Invasive Species Affect Ecosystems?
Invasive species can affect native populations through competition, predation, herbivory, disease transmission, parasitism, or changes to habitat. The effect depends on the species involved and the relationships already present in the community.
Competition is especially important when an invasive species uses the same limiting resources as native organisms. If the invasive species obtains resources more effectively, native populations may decline. Invasive species can also alter food webs by becoming a new food source or predator, or by changing the abundance of organisms at other trophic levels.
Shared resources
An invasive species may compete with native organisms for food, space, light, water, or nesting sites.
New consumer pressure
Native organisms may lack effective defenses against a newly introduced predator or herbivore.
New pathogens
Introduced organisms can carry or amplify diseases that affect native populations.
Invasive Species and Biodiversity
When invasive species reduce native populations, they can contribute to declines in biodiversity. If a native species disappears from a local community, species richness decreases. If the invasive species becomes extremely abundant, species evenness may also decrease because the community becomes dominated by fewer organisms.
Invasive species are therefore one potential driver of biodiversity loss, alongside habitat loss, overexploitation, pollution, and other environmental pressures.
On an ecology test, an invasive species can connect population growth → competition → community change → biodiversity loss.
How Are Invasive Species Managed?
Management strategies depend on the organism and ecosystem. Preventing introduction is often more effective than trying to control a species after it becomes widespread. Early detection can also allow populations to be removed or reduced before they become difficult to manage.
Control methods may include physical removal, habitat management, targeted chemical treatments, biological control, or combinations of strategies. Biological control involves using a natural enemy to reduce the invasive population, but it must be carefully evaluated because introducing another species can create additional ecological problems.
Prevent
Reduce the chance that a non-native organism is introduced to a new ecosystem.
Detect early
Find new populations before they spread widely.
Control or remove
Reduce population size or impacts using an appropriate management strategy.
Common Misconceptions
If You See This on a Test, Think This
Quick Practice
1. What makes an invasive species different from a non-native species?
2. How can an invasive species reduce a native population?
3. Why can invasive species reduce species richness?
4. Why is prevention often an important management strategy?
5. Why must biological control be used carefully?
Key Takeaways
- A non-native species occurs outside its historical range.
- An invasive species is non-native and establishes, spreads, and causes significant harm.
- Invasive species can affect native organisms through competition, predation, herbivory, disease, and habitat change.
- Invasive species can alter population sizes, community structure, food webs, and biodiversity.
- Prevention and early detection can be important parts of invasive-species management.
- Control strategies must be chosen carefully because ecological interventions can have unintended effects.
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