Invasive Species (College Board AP® Environmental Science) : Study Guide

What is an invasive species?

Definition of an invasive species

• Invasive species are organisms that live and thrive outside their natural habitat

• They are introduced either intentionally or unintentionally by human activities

• A species is considered invasive when it

  • threatens native species

  • disrupts ecosystems

  • causes economic harm

Characteristics of invasive species

• Often adapt quickly to new environments

• Frequently lack natural predators

  • This often allows their populations to grow unchecked

• Many are generalist species

• Often have high reproductive rates

Examples of invasive species

• Kudzu vine (native to Japan and China, invasive in the U.S.)

  • A fast-growing plant that smothers native vegetation

• Zebra mussels (native to Eastern Europe, invasive in the Great Lakes, U.S.)

  • Disrupt aquatic ecosystems by outcompeting native mussels and clogging water pipes

• Burmese pythons (native to Southeast Asia, invasive in the Florida Everglades)

  • Prey on native mammals and birds, reducing biodiversity

• Cane toads (native to Central and South America, invasive in Australia)

  • Introduced to control pests but became a major ecological threat

Problems associated with invasive species

How do invasive species cause problems?

• Invasive species can significantly disrupt ecosystems

  • This often leads to biodiversity loss and ecological imbalances

• Many invasive species are generalist, r-selected species

  • This means they reproduce quickly and adapt well to new environments

  • This means they often outcompete native species for resources

Environmental problems caused by invasive species

Competition with native species

• Invasive species outcompete native species for food, space, and other resources

  • Example: Asian carp in U.S. waterways consume vast amounts of plankton, leaving little food for native fish

  • Example: Miconia (Hawaii & Pacific Islands)—known as the “green cancer,” this invasive tree forms dense canopies that shade out native plants, reducing biodiversity

    • It also has a shallow root system that facilitates soil erosion

Predation on native species

• Some invasive species prey on native species

  • These native species lack evolved defenses to the new predators

  • Example: The Indian mongoose was introduced to various tropical islands, such as Hawaii and Fiji, to control rats but ended up preying on native birds and reptiles, causing severe biodiversity loss

Disrupting food webs

• Removing or replacing a key species can alter the structure of an entire ecosystem

  • Example: Rabbits in Australia —introduced by European settlers, they have overgrazed native vegetation, leading to habitat loss for many native species and disrupting predator-prey relationships

Habitat destruction and alteration

• Some invasive plants and animals change habitats, making them unsuitable for native species

  • Example: Prickly pear cactus (Australia)—originally introduced for agricultural purposes, it spread uncontrollably and transformed vast areas of native grasslands into dense, impenetrable thickets, making the land unsuitable for native wildlife and livestock

Introduction of diseases

• Some invasive species carry new diseases or parasites that native species have no immunity to

  • Example: American chestnut blight, introduced from Asia, wiped out nearly all American chestnut trees

Reduction in genetic diversity

• When invasive species hybridize with native species, it can lead to loss of genetic diversity

  • Example: Hybridization between invasive and native trout species has reduced pure native populations

    • Invasive rainbow trout have hybridized with native cutthroat trout in the western U.S., particularly in states like Montana and Colorado

    • This has led to genetic dilution, reducing the number of pure native trout populations

Controlling invasive species

• Early intervention is crucial to prevent the spread of invasive species and minimize long-term impacts

• Control methods must balance effectiveness, environmental impact, and cost

Methods to control invasive species

Physical removal

• Manually removing invasive species by hand, trapping, or mechanical methods

• Effective for small populations but difficult for large-scale invasions

Biological control

• Introducing natural predators, parasites, or diseases to control invasive species

  • Example: Cactoblastis moth larvae (native to Argentina) introduced in Australia to control invasive prickly pear cacti

• Risks: If not carefully managed, biological controls can harm non-target species

Chemical control

• Using pesticides, herbicides, or poisons to kill invasive species

  • Example: Applying herbicides to control Japanese knotweed in many parts of the United States

• Risks: Can harm native species and pollute water

Legislation and prevention

• Regulating trade and transport to prevent the introduction of invasive species

  • Example: Strict ballast water regulations for ships to prevent transport of invasive aquatic species

• Public awareness campaigns help prevent accidental introductions

Habitat restoration

• Restoring native ecosystems to make them more resilient against invasive species

  • Example: Replanting native vegetation after removing invasive plants

  • Encourages native species recovery and can help to restabilize ecosystems