Why are invasive species so good at being invasive?

Zebra Mussels growing on a native mussel. Photo Credit: Minnesota DNR

Author: Brittany Maule 

Every year, invasive species (species not native to an ecosystem) cost the United States more than $120 billion dollars in damages¹. You’ve probably already encountered some invasive species without even knowing it. Do these names ring any bells? Zebra mussels, Asian carp, Eurasian Milfoil, Burmese Pythons, Sucker Mouth Sea Lampreys, Lionfish and the list unfortunately goes on. These troublemakers are problematic in ecosystems for a variety of reasons. They can decimate natural populations of important organisms such as with the lionfish, or cause damage to wastewater treatment plants like the fast-growing zebra mussel. Because they cause so many problems, a lot of work has been done to try and eradicate these species as well as limit their spread. Hence, the billions of dollars spent on invasive species each year. But why are these organisms so detrimental? What makes them so good at getting into places we don’t want them to and cause problems?

The answer to these questions lies in some general characteristics that most invasive species share.  

·       High reproductive output². Most invasive species can reproduce at high rates, and very quickly. For example, one female zebra mussel can lay 40,000 eggs per reproductive cycle. This makes reducing numbers difficult when so many new organisms are released into the environment.

·       Fast growth rate². The larval or juvenile stage of a lot of invasive species can grow quickly, often more quickly than native species. The faster an organism can take up nutrients the easier is for it to out-compete other species and increase its numbers.

·       Tolerant in different conditions². Often, invasive species can live in a variety of conditions, making it easier for them to spread to different types of systems. For example, if an organism can tolerate a wide-range of temperatures, they could spread to lots of different areas across the U.S. because they aren’t constrained by this factor.

·       Omnivores, or just not-picky eaters². Invasive species can often feed on several different food sources, making them more effective at using the resources in an environment. This spells trouble for native species who then can’t use those nutrients to grow and reproduce.

In addition, not only does the invasive species need to be good at invading and establishing itself, the environment it is going to has to be an ideal place for it to thrive. For example, not all non-native species that move to an area will become invasive species. Environments that allow invasive species to establish share some characteristics too.

·       Lack of predators². One thing that is often the cause of a large input of invasive species is a lack of natural predators that can suppress invasive species explosive growth. For example, lionfish were introduced into the Caribbean around 1985, and have since decimated natural reef populations because no predators in that area naturally eat lionfish.

·       Highly connected. Systems with connections to other nearby systems are a good space for invasive species to thrive because it is easier for them to spread. For example, The Great Lakes have had several invasive species run rampant and cause issues because of how connected the waterways are to themselves and other rivers, streams, etc.

Management of these species can be tricky, and often extremely difficult to do without harming the natural organisms that live in an ecosystem. Current management efforts can include anything from physical removing a species such as pulling plants out of the soil, to using chemical and biological controls such as introducing predators to try and suppress species growth. While removing species on a wide-scale seems like a daunting task, there’s actually a few things you can do to stop invasive from spreading.

·       Clean off your boots when hiking

·       Empty any water in your boat and clean off the outside before and after entering a waterway

·       Don’t transport firewood across state lines

·       Don’t release pets into the wild

·       Check whether a plant is considered invasive before planting

Check out these resources for more information about the invasive species and their economic impact:

(1)    U.S. Fish and Wildlife Service. “The Cost of Invasive Species.” January 2012. Available from: http://www.fs.fed.us/pnw/invasives/

(2)    Cary Institute of Ecosystem Studies. “What makes invasive species so successful?” n.d. Available from: http://www.caryinstitute.org/sites/default/files/public/downloads/lesson-plans/hre_lesson_3_summary_slides.pdf