Nuisance species can outcompete and displace native species

Justin Perkins
MCWC Project Manager/Watershed Specialist
Justin Perkins, MCWC Project Manager/Watershed Specialist

Nuisance species are detrimental to watersheds and to the native species within them. During eras of human expansion, settlers and homesteaders often brought crops, plants, trees and fish species with them from their places of origin. Species were introduced into new landscapes without any consideration of the environmental repercussions. Many of these non-native species thrived in their new environments and established themselves in their new landscapes, often outcompeting and displacing native species.

Non-natives species are defined as populations of species that are living outside of their naturally occurring range. Most commonly, these species were introduced by humans for recreational, food consumption, or nostalgic purposes. Generally, they were not introduced with any malice, just lake of forethought or ignorance of the unintended consequences.

Nuisance and invasive species are often introduced, but an introduced species isn’t always nuisance or invasive. An introduced species is a non-native species that has economic, recreational, or biological value whose benefits outweigh any harm to native populations or ecosystems. Introduced fish species such as rainbow and brown trout are larger than native cutthroat trout, making them popular target species for recreational angling.

An invasive species is a non-native nuisance species that outcompetes, harms, displaces, or creates undesirable conditions for native populations. Nuisance species are invasives that require active suppression, often at great expense, due to their potential for ecosystem and biological harm.

Colorado’s early history of limited management and lack of regulation for nuisance species has allowed many non-native species to establish themselves. Concentrations of these species are found alongside areas of high human use. Species have been introduced since the 19th century, many populations of non-natives are long established and wide ranging. At this point many are impractical to remove.

Non-natives often persist because they have no natural predators, they may have the ability to outcompete natives, and are often easily transferable. Transfers can occur from something as simple as a seed attaching to your hiking shoe at one location, then detaching during your next hike at a different location. Aquatic organisms can attach to gear or boats and be transported unknowingly to new bodies of water. Intentional introduction of species also occurs, such as people dumping home fish tanks or bait buckets into bodies of water. The introduced plants and fish can propagate and potentially take over the ecosystem.

Invasives can be larger in size, have higher food consumption drives, superior mobility, or advanced morphologies that give them a competitive edge. Non-native species can also have wider tolerance ranges for temperature, drought, or other environmental parameters. Having a wider tolerance also gives them a long-term advantage in adapting to a changing climate.

Introduced species can also be vectors of disease. When they are introduced into a new environment, they can bring disease with them. Native and established populations may be exposed to new diseases that they have historically never encountered and do not have the ability to fight off.

Every ecosystem has a limited number of resources, non-native species can consume resources historically used exclusively by native species. For example, in an aquatic environment such as a lake, an invasive mussel species can interrupt the lower trophic levels by consuming oxygen and nutrients, leaving nothing for native organisms. Invasive plant species, such as tamarisk may consume up to 200 gallons of water per day, removing scarce resources with no benefit to native ecosystems or local economies.

Human transfers of non-native species occur both unwittingly and deliberately. Most often introduction occurs unintentionally, as with tiny mussels attached to boat hulls, propellers or in live wells. Unfortunately, some bad actors deliberately move fish and other species between bodies of water for personal benefit without permission from aquatic managers.

Education, outreach, regulation, and enforcement are key to altering the behavior of people who illegally transport and introduce nuisance species. Nuisance species cause severe ecological impacts by competing with and displacing native species. Removal of nuisance species is very costly and labor intensive. The best approach for managing nuisance species is to prevent species from being introduced in the first place.

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