An invasive species is defined as a species that is:
non-native, or alien, to the ecosystem and
whose introduction causes or is likely to cause environmental or economic harm, or harm to human health.
Invasive species can be plants, animals or other organisms, such as microbes. Invasives are dangerous because they often arrive in environments better suited to them than the ecosystem they evolved in. They thrive because of different seasonal patterns, water patterns, or lack or competition or predation, and can outcompete native species. Pushing natives to extinction reduces overall biodiversity. Estimates suggest that over half of the threatened and endangered species listed under the Endangered Species Act have been negatively impacted by invasives.
Human actions, whether accidental or intentional, are the primary cause of invasive species introductions.
Some of the invasive animal species that have been found in Great Basin National Park are the brown trout, brook trout, rainbow trout, Lahontan cutthroat trout, house mouse, wild horse, House sparrow, European starling, and wild turkey.
There are over 25 species of non-native plants in Great Basin National Park, including cheatgrass, spotted knapweed, crested wheatgrass, bull thistle, and musk thistle. Not all species are equally harmful to the ecosystem, so only those that pose the greatest threats are targeted for control. Control measures usually involve pulling or spraying plants.
Plants are introduced via many routes. Some are planted in gardens or during roadside stabilization projects. Others are introduced accidentally as contaminants in seed, animal feed, or even packing material! Nonnative seeds and plant parts are often spread by being carried on the hooves or hides of animals, in the doors or undercarriages of vehicles, or on hikers' apparel. The fact that some plants are continuously being re-introduced into the park poses additional problems.
You can help control non-native plants in the park by scrutinizing your shoes, socks, and pants legs for "hitchiking" seeds.