When we think of non-native species the immediate and almost programmed response is “they are bad!” This thinking is backed up by study after study showing that whether it is a non-native plant or animal species that they have serious ecological and economical impacts worldwide. These non-natives, often referred to as invasive species because of their ability to spread unchecked have been shown to decrease biodiversity, disrupt ecosystem functioning as well as displace native species. They are estimated to cost around $300 billion dollars globally as they are costly to manage and can negatively impact industry such as forestry, agricultural, and tourism. However, does this mean that all non-native species are bad?
Before we skewer all non-natives species let’s stop to take a moment to define some words. Non-native: not indigenous or native to a particular place. Therefore, Native: of indigenous origin or growth. Interesting enough the dictionary makes no distinction between people, plants, and animals for the definition of non-native however, for native you also get this alternative definition: a person born in a specified place or associated with a place by birth, whether subsequently resident there or not. I believe that bolded statement is a very important one. Why do we make such distinctions for people but not for other species? Doesn’t every creature no matter where it lives compete for land and resources? How is one organism good in one environment but not in another? Let’s take look at some examples of the good, bad, and indifferent when it comes to non-native species.
Let’s start with a couple examples of the bad. Kudzu is a fast growing, nitrogen fixing vine that originated in China and is infamously known as ‘the vine that ate the south”. This is an apt name as the vine has taken over large portions of the southeast U.S. It voraciously swallows landscapes in its path seemingly outcompeting all in its way with an astounding annual spread of 150,000 acres annual. To put that in real world context that means in one growing season in the southeast would be enough to take over the whole park of Santa Monica Mountains National Recreation Area. Despite its nasty reputation this vine was brought over intentionally as an ornamental plant in the 1800’s for use around homes and as erosion control.
Some other examples of a destructive non-natives are the zebra and quagga mussels. Both originally from Eurasia, these little bivalves have been causing a lot of trouble in the Great Lakes since being inadvertently introduced. They clog up pipes, damage boats, and cause cuts or abrasion to humans when stepped on or rubbed against. As there are few predators compared to where they originate these little guys have been left to spread virtually unchecked.
There are many more examples of the bad but I would like to move on to the indifferent. What, do I mean by indifferent, well it’s clearly not scientific term but I mean non-native species that “invaded” but have little to no cost to natives. This example comes from my home state of New Jersey and all starts at the Jersey shore with the introduction of the Asian shore crab. Over twenty years ago when this crab landed in NJ it quickly spread up and down the Atlantic coast. Many worry and still do that this crab will negatively impact natives, as it has been known to prey on juvenile American lobsters. However, recent research has shown that they actual enhance other natives such as common periwinkle, small crustaceans, blue mussels, and barnacles in the cordgrass-ribbed mussel communities that they prefer. While there are positives and negatives to their introduction it is not a story of doom and gloom but one of trade-offs that occur in any natural system.
Another example comes from the great white north of Canada, when a small fish called the Round Goby moved in (see picture above with “bad” fish). When it was first introduced into the St. Lawrence River biologist where concerned because it was less parasitized than native species which would translate into a competitive advantage. However, over the last 15 years the parasite population has increased on the Goby and now matches that of native species. This suggest that the Goby, although invasive, is experiencing the same selection pressures as the native fish and therefore is possibly integrating itself into the food web in the lake.
So, now on to the good. Is there such a think as good invasive species? Well, here are just a few that we take for granted but we depend upon during every growing season. They have become such staples of our economy and agriculture that we hardly ever think to point the finger at them. So what are they, the big three in my opinion, honey bees, earthworms, and grains. They are all from Europe and were all imported, two out of the three were conscience decision (I’ll let you figure out which ones). Just think how we are concerned for pollinators and especially honey bees but do we care that they are non-native? How about all of our cereal grains or the worms we depend on in our gardens. If their benefits are overwhelming positive then not many care if they have also some negative impacts.
So when do species become native? Are they native if born here regardless of where they once resided? Do they need to become culturally or economically important first? Do they need to reside in the area before historical record or do they need to evolve for millions of years in one spot? When is it alright for them to spread and conquer, what time scale is appropriate? How do we decide? It is certainly a messy set of questions.
In my opinion we are at a crossroads of how we conduct science and how we label species. A lot of time and effort has been spent trying to reduce or eradicate invasive, non-native species, many times after they have become a significant problem. This strategy in most cases has had little success. Current efforts look towards early detection and quick eradication before they become a further threat. However, we are making decisions based on a human construct of good and bad that doesn’t exist in clear terms. Is a native monoculture of cattail marsh or red maple swamps any better than a non-native monoculture of a phragmites marsh or a field full of tree of heaven? Depends who you ask. With the inevitable onslaught of climate change and human dispersed non-natives is there room for rigid dogmatic views on species or is it better to be flexible with our thoughts and actions when it comes to non-natives?