Native Versus Non-native

We frequently hear the terms “native” or “indigenous,” referring to a people or a plant or an animal that are native to a place—i.e., were born or originated there. These terms are often used in conjunction with the contrasting or opposing terms “non-native” or “invasive.” In the deep past the migration of species was so slow that all living things were pretty much considered native, but now we humans are in constant and rapid movement throughout the world, taking countless flora and fauna with us, so that native species are continually encountering non-native competition—sometimes with tragic effects.

A native species is one that originated in a given location. It came into being (the root of the word native is the Latin word natus, born) in its indigenous place; it evolved there. In the evolutionary process, species last only if they find a niche and come into balance with many other species; i.e., settle into a complementary existence. Over time an equilibrium is reached, and if the environment remains stable for a while, the various native species maintain that cooperative network, wherein each of them fulfills a useful role.

A non-native species—once indigenous to its own locale—is one that migrates to a foreign place. It then finds itself in strange territory, looking for a niche to occupy. In doing so, usually one of three outcomes will happen: (1) it can’t fit in or compete and dies out, (2) it finds a niche and settles in (sometimes adapting and changing itself and its new home in the process), or (3) it enjoys a considerable advantage in its new locale (finding little competition there) and it runs amok. The third case is the one that often gets labeled “invasive species,” because it moves in, upsets the delicate balance, and takes over. Some examples of invasive species in the US are kudzu vine, gypsy moths, Dutch elm disease, house wrens, avian influenza, water hyacinth, zebra mussels, etc., etc.

This process of native and non-native species competing with each other is as old as life itself. Species have always migrated into new territory and found themselves competing against native critters. The difference lately is that the migration rate can now be at the speed of an airplane. Think of the recent worldwide spread of swine flu.

Thus indigenous species are constantly and suddenly being exposed to strange invaders, often at a very bad time for many of them: when their native environment is already under stress and being degraded. Even in the quite recent past species had the leisure of many thousands of years to adapt to the changes in their environment or the encroachment of competitive species. Now they are being assaulted far more often and being forced to deal with these changes in days and months, rather than eons.

One of the most threatening invasive species on Earth is Homo sapiens. We are indigenous only to Africa, yet we have spread to every corner of the globe—overnight in nature’s time scheme. In every case we’ve bested any native species we’ve encountered, driving many of them to extinction. The Americas once were home to dozens of mega-fauna species (mammoths, ground sloths, giant bears, etc.), that disappeared soon after humans arrived on these continents, thousands of years ago. Passenger pigeons once blackened the skies above North America, until people shot them into oblivion, a century ago. Australia was home to several species of giant flightless birds, until people migrated there, 45 thousand years ago and found them easy pickings. The list could go on for pages.

We humans have relentlessly altered our environment, often by rooting out native plant species, as we create vast areas of cultivated products. Some would say that this most invasive species of all is running amok. In every case in the past, when an invasive species has exploded its population far beyond a sustainable level, nature has eventually forced things back into balance. The invaders’ numbers precipitously crash—think invasions of locusts. The gypsy moth relentlessly marched south from New England in the 19th century, rapaciously attacking and killing native oak trees, until it finally got checked by a native species of fungus in the Middle Atlantic states, just a few years ago. The crash of an out-of-balance non-native species seems inevitable. I wonder what Mother Nature has in store for Homo sapiens.