By Caitlin Muller and Benjamin Hansknecht- 2018 SLELO Early Detection Team.
41% of threatened or endangered species are in demise as the result of invasive species introductions (Pimentel 2000). By pushing out native rivals, invasive species often disrupt food webs, alter the ecology of the local ecosystem, and can ultimately lead to the extirpation of other native species. It is a global conservation issue with large-scale ramifications and one important question to address is why these species are so successful when introduced to new locations and environments.
By relocating living organisms to new habitats, it is frequently the case that their destination is outside the range of their native predators and diseases, two of the biggest restrictions on population growth. Without these limits, it is possible for species to rapidly reproduce and expand their populations, whether they are continents away from their native range or as close as the state next door. In this way, invasives can completely displace native species and create monotypic stands, or monocultures. This environment decreases the biodiversity of the area and in turn disrupts the local food web. Negative impacts to the habitat and resulting decreases in biodiversity, in turn, produce decreases in ecosystem quality.
For example, Eurasian watermilfoil outcompetes native aquatic plant species for space and nutrients. By out-competing the natives and through sheer abundance it creates low oxygen environments via decomposition where native fish and aquatic invertebrates have difficulty surviving. This in turn limits the food supply of organisms higher up the food chain which feeds on these species.
Some invasive species impact health of animals, invertebrates, plants, and humans. Swallow-wort causes a problem for livestock when ingested. Goats, which are sometimes used in invasive species control, cannot ingest swallow-wort as it causes illness. Monarch butterflies will lay their eggs on swallow-wort plants because it’s a member of the milkweed family, but when the larvae hatch they will not survive due to the host specificity of the caterpillars. Other plants are affected by swallow-wort due to its allelopathic tendencies. By releasing toxins into the ground, swallow-wort inhibits other native plants from establishing. The sap of giant hogweed and wild parsnip will cause severe skin irritation and blistering.
Impacts of invasive species such as these can be reduced if action to prevent their introduction and spread is taken. Raising awareness of invasive species is a key component to prevention; in addition, early detection of invasive populations and the implementation of a rapid control response are vital to stopping their spread.