Invasive and non-native species

This is the first post of several where I will explore invasive and non-native, or introduced, species. This is a big topic in the management of natural resources and the control of such species is a big part of the work we do at Pearl Creek Farm. Like any scientific topic, there is disagreement about these terms, what the concepts really mean, and how they apply in the real world. Naturally, I have my own opinions about them, but don’t take my word for it! Do your own research and ask your own questions.

Invasive species are those organisms that tend to crowd out other species, occur in high numbers or densities in certain situations, or somehow alter the natural environment in a significant way so that natural processes can no longer function normally.

Egregious examples from the plant world include tall fescue, Japanese honeysuckle, and my personal nemesis, multiflora rose. These species grow aggressively and crowd out native plants. You may have also heard of zebra mussels, which tend to grow in such large numbers that they clog water intakes and disrupt other structures. Take a look at some funny videos of Asian carp. These fish tend to jump out of the water when motor boats are near, sometimes injuring boaters. Unfortunately, they love our North American waters, will reproduce rapidly, and tend to displace native fish.  

Non-native species are those organisms that historically do not naturally occur in a particular ecosystem. While this seems like a black and white determination, it’s not always clear if species are native. For example, watercress is a common plant growing in cool water in both Europe and North America. It is commonly found in Missouri springs and it is actually rare for a spring to be without it. It is unclear if Europeans brought the plant with them or it has always grown in North America.

The list of non-native species in Missouri and North America is very long. In fact, you might not even think of this when considering species such as house sparrows, starlings, pigeons, dandelions, wild asparagus, ox-eye daisy, and the lowly house mouse.

Rainbow over a vast field of soybeans growing in a former prairie
Rainbow over a vast field of soybeans growing in a former prairie

Most of the plants we use in landscaping and agriculture are also non-native. Usually, they thrive only in controlled gardens and crop fields and do not become a problem in natural ecosystems. If they do, they are considered naturalized or escaped. Non-native species used as crops or landscape plants are not my primary concern in this blog series, but they are often the source of new invasive species. Please “Grow Native” instead of using landscape plants from Lowe’s or other big box nurseries!

Although these two terms (invasive and non-native) are often used interchangeably, they are different and care should be taken to be clear about your meaning when using them. To be fair, nearly all invasive species, particularly the worst ones, are also non-native, but there are exceptions. Also, there are many non-native species that are not invasive. In fact, most non-native species would not be classified as invasive. Instead, they seem to fit into our natural environments without seeming to cause problems.

In future posts, I’ll explain some of the reasons why species become invasive, give examples of invasive species that are actually native, talk about subsidized predators such as raccoons, feral cats, and wild hogs, and explore the definition of our own species. Are humans non-native and / or invasive?

Posts in this series:

1. Invasive and non-native species (this post)
2. Why are invasive species so successful and so bad?