In my first post on non-native and invasive species, I explained the definition of these terms, gave several common examples, and explained why these terms are not synonyms. Let’s leave the general topic of non-native behind for a bit and concentrate on invasive species only. What makes them “bad” and why are they so successful?

There are many specific reasons why an organism might become invasive. Almost all of them boil down to the fact that these species suddenly find themselves free from the predators and disease that served to keep their numbers in check in their natural range. Without these limiting factors, a species can grow uncontrollably. Since the existing native species still must contend with these factors, they are at a competitive disadvantage. Furthermore, native species are not adapted to compete with the newcomer.

All non-native species use up limited resources that would otherwise be available for native species. Invasive species often use these resources, including space, so aggressively that they can prevent other species from growing at all. In this way, some invasive species form vast monocultures, effectively preventing other species from being present at all, thereby reducing overall diversity.

Often, invasive species originate from areas that have a long history of civilization and the land-altering practices that accompany it. These species might actually be adapted to human habitations and might not even be able to survive in “natural” conditions. Because modern humans tend to alter landscapes to suit their purposes, and usually in similar ways, these species have an automatic advantage over the species that naturally occur in an area.

But, why does this matter? Isn’t “survival of the fittest” a law of nature? If the native species cannot compete, perhaps they should be replaced! Others are argue that humans have mucked up the world enough already and we should just let “nature take its course” without interference. Why isn’t this a valid position?

This is indeed a good philosophical question. The primary reason is the effect that we humans have on the natural world. We are so numerous and have successfully adapted to practically every ecosystem and habitat on earth. We are homogenizing the world and bringing our invasive species along with us everywhere. Diverse ecosystems that have evolved over millenia are being replaced with fields, yards, cities, and parking lots.

The plants and animals that have evolved to live in a natural world are too stressed to compete against the various invasive organisms that follow us. Furthermore, many of these species, including mice, rats, cats, dogs, cockroaches, and various ubiquitous “ground covering” plants are actually spread and subsidized by humans. How do native species stand a chance without our active help?

From an aesthetic standpoint, it’s desirable to save uncommon and natural species, to ensure these ecosystems survive as intact as possible into the future. But, there are selfish reasons to save these species. They provide numerous ecological services to us, including carbon sequestration, pollination, flood control, air and water filtration, recreation, and countless others. Allowing invasive species to replace their native counterparts is not in our best interests in any conceivable way.

Unfortunately, fighting invasive species is an uphill battle. They have many advantages and constant control is needed to keep them in check. In a future post, I’ll discuss the methods used to control these species and some things you can do to help.

Posts in this series:

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