Last week the New York Times (<– read article here) posted an interesting opinion piece about the nutria (Myocastor coypus), a rodent native to South American that was released into the wilds of Washington State (and others) in the 1960s. It brought up the question, how long does a species have to be in an area before its considered native? Haven’t many species, humans included, migrated to various parts of the world? Isn’t evolution by natural selection about adaptation and the strong surviving? What makes a species foreign or native?
This post is going to be about my opinion on the matter. I’m open to my mind being changed, but support your opinions if you want to contribute! I find this topic very interesting and certainly debatable, which of course is half the fun.
It is an interesting question, “What makes an invasive species?” Well, it’s invasive if it’s not native and even more so if it harms the native species, right? But what about those non-native species that don’t much bother the natives? And where did the native species come from? If you go back far enough, everything started in the sea, and those first semi-terrestrial species could certainly be considered non-native to the land, right? And since all evidence currently points to Africa as the continent of human origin, humans had to migrate to all these other places. We’ve certainly caused more than our fair share of damage and extinctions, so, by definition, humans are invasive species. Right? Where is the line?
Humans aren’t the only species that have gone from their point of origin to other places. Modern horses evolved in the Americas and only entered Eurasia by migration. However, fossils of the first known equid, Hyracotherium, can be found spread out across the entire northern hemisphere, back when North America and Europe were actually connected, though separating, landmasses. And, of course, there is a huge debate about whether horses currently in the Americas are wild or feral, which I discussed in my recent post Wild, Tame, Feral and Domesticated.
There is a debate as to whether rabbits and hares started out in Asia or the Americas, but either way they had to migratefrom one place or the other. Wolves, now found across both the Americas as well as Eurasia, probably started at just one point on the map. Yet, horses are still considered native to Eurasia, wolves and rabbits are considered native to most of the places they’re found (rabbits are not considered native to Australia, as a clarification). Again, where is the line?
Species swaps between the Americas and Asia occurred during the various periods of time there was a land bridge between what is now Alaska and Siberia, called the Bering land mass. It’s also possible there were land bridges between other places, such as continents and islands. How, you might ask? During ice ages sea levels drop as the water is basically sucked up into glaciers. A land bridge can be made out of ice connecting two areas or from exposed land. There is a hypothesis that were was such a bridge between India and the island of Sri Lanka called Rama Setu, or Adam’s bridge.
I think, at least when it comes to continents, the vast majority of migration occurred by land. Species don’t jump from one place to another place overnight, particularly if those locations are quite far apart. Most of these migrations (and I’m excluding species humans brought to various places right now) were slow going. Walking hundreds or thousands of miles takes time, after all. It’s been estimated that even the human migration out of Africa, into the Middle East, and over to Southeast Asia only occurred at a rate of about a mile a year. The point is, these migrations didn’t happen overnight, it was usually a slow process of species inching along. More adaptable species, such as humans, probably moved at a faster rate than those that were more dependent on a specific type of food or habitat.
Hordes of animals don’t come charging into new territories intent on invasion, it’s more likely a herd or pack here and there or a few individuals following the food; in other words, small, slow migrations. Small, slow migration can allow the new area, and the species already there, some time to adapt to the invader. They aren’t automatically overrun. No matter how much time to adapt a species may have, sometimes they just can’t evolve fast enough and they go extinct. This is a natural event that can happen because of a new species or because an old one evolved too fast to keep up with. It’s nothing new.
Species introduced by humans usually occur in small numbers too, though I’ve noticed many of those species are prolific breeders. Yet there is also no slow creeping into the area but a sudden thrust. Less time to adapt. Deal or die.
What about the “survival of the fittest”? Does it matter where the species came from? If it can outcompete the native species, doesn’t that just mean it’s better suited? An importany point here is that it’s not just about one species, it’s about the entire ecosystem. Species that are considered native have evolved in a way to co-exist with other species and live in a balanced community. It is not one species dominating all the others to the point of driving them to extinction. Maybe this happened when species first migrated, but now things are balanced again.
Yet, if such an ecological distribution did occur during or after a migration, what’s the difference between one in the past and now? It would still cause a period of imbalance, of adaption, and of possible extinctions, right? Right. But did these new species arrive here by their own means? Did they walk or fly, following food sources and habitat expansion, in a slow migration to a new home? Or did they get brought over here by humans, rather abruptly, and thrown into the environment, giving the ecosystem and other species far less time to adapt and evolve?
I like the nutria discussed in the New York Times article, I think they’re cute. But I personally still think their non-native. Maybe, just maybe, in a few hundred years or more, when they and their neighbors have balanced out and adapted to each other, they can claim the title, but right now everything is unbalanced. These rodents haven’t decided to be rude and barge in, they were snatched from their homes and tossed over here. It’s not their fault, to be sure, but that doesn’t affect their status of non-native.
Part 2 next week…