One of the factors that decrease biodiversity is the introduction of invasive species. However, the success of an invasive species can also be due to a degraded environments. A stressed ecosystem can become unbalanced. In recent news, the introduction of Asian pythons to the Everglades (from pet owner releases) has resulted in decreases in mammal populations. The python likes the new habitat created by the draining of much of these wetlands. After land use change, invasive species are the second greatest threat to ecosystems. So, let’s go ahead and take a closer look at invasive species.
Invasives Defined
In invasive species must meet the following criteria, as defined by executive order 13112 signed by President Clinton:
- A non-native (or alien) to the ecosystem under consideration
- A species whose introduction causes or is likely to cause economic or environmental harm or harm to human health
Africanized Honey Bees are a classic example of invasive species. The species, created by humans, migrated into the U.S. from central America. The bees kill off native honey bee species, and are poor pollinators and much less productive than native bees. (USDA)
Both criteria must be met. Invasive species can be plants, animals, and other organisms (e.g., microbes). Human actions are the primary means of invasive species introductions. While most invasive species come from different continents, they do not have to--a species from Oregon could become an invasive species in Indiana, or a species from northern Indiana could become invasive to southern Indiana.
Problems Caused
Invasive species are thought to cause economic losses in excess of $100 billion dollars a year--not counting the cost of degradation to ecosystems. In invasive species will usually devastate the landscape by:
Eating plant species: Animals, insects, fungus, or microbes can devour massive amounts of native plants required as a food source by humans or animals. Native animals can starve to death as a result.
Destroying other plant species: Plants can destroy other plants by starving them of sunshine, secreting poison in their root system, or stealing excessive nutrients or water from the soil.
Destroying other animal species: Insects may destroy or eat other insects that are necessary for plant pollination, invasive animals may devour other native animals who lack the ability to defend themselves from the invasive.
Invasives can totally destroy a landscape. Invasives usually take hold when their is an abundant native food source or landscape that allows the species to flourish AND the landscape lacks any natural predators.
Invasive Transport
Most invasives are introduced by humans. There are several pathways for invasives to enter a new ecosystem:
- Abandoned pets. Piranhas and alligators have been found in waterways in central Indiana. Why? Because someone dumped their unwanted pet into a river or pond. A few abandoned pets can easily grow into millions of invasive species.
- Ornamental plants. People bring back all kinds of crazy plant life when traveling abroad, and U.S. Customs only catches some of this material. Other non-native plants can be easily bought from local nurseries. Once the plant or its seeds are outside, they can take over an ecosystem.
- Purposeful introduction. Some plants and animals were purposefully introduced into native ecosystems to provide some benefit, like erosion or pest control. In some cases, this introduced creature itself becomes a pest when it takes over the landscape.
- Accidental introduction. Some plants and animals hitchhike their way into new ecosystems. Microbes and insects can travel in cargo, in animals (or people), or in plants. Aquatic life can hitch rides in the ballast water inside shipping freighters. Some animals have even hitched rides on cargo ships.