|Common starling--a master invasive species. Photo|
from New Zealand Birds Online
Invasion biology is the study of the introduction, infiltration, establishment, and control or elimination of non-native species in a given eco-system. It is a discipline that has come about primarily as a result of international trade and travel, which has increased the mixing of species worldwide. In many places, these biological “invaders” have raised concerns, particularly where agriculture and other industries find themselves threatened by the establishment of “alien” species, or where control of invasive species can, in and of itself, become an industry.
The science of invasion biology began in 1958 with the publication of Charles Sutherland Elton’s book The Ecology of Invasion by Animals and Plants. An animal ecologist and research fellow at Oxford University, Elton was given the task of finding ways to control the proliferation of rats and mice in stored grain during World War II. After the war, he continued his research into the connections between invasive/pest animals and human activity, and may also have been the first to suggest that invasive species might impact on native species and biodiversity in general, particularly when introduced into isolated habitats.
A “war” against invasive species was declared in the US in 1999 when an executive order “directed several federal agencies ‘to prevent the introduction of invasive species and provide for their control and to minimize the economic, ecological, and human health impacts that invasive species cause.’” (see here).
Some invasive species are clearly destructive. One example is Dutch elm disease, caused by a fungus native to Asia where trees are naturally resistant to it. The disease, which is spread by bark beetles, first appeared in Europe in 1910, and over the next century spread to North America and New Zealand. By 1990, few mature elms were left in Europe or the UK, and vast swathes of North America’s elm forests had been destroyed. Today, disease-resistant elms are being bred, fungicides can be injected into infected trees, and a vaccine has been developed for injection into non-infected trees that seems to provide some protection against the fungus.
Other invasive species have been of benefit to nature and sometimes to man. Honey bees, for example, are native to Europe, but are “non-native invasives” in the Americas and in countries like Australia and New Zealand; much of our agricultural pollination and our honey industries depend upon them. Many “invasive” plants and non-native garden plants gone feral are enjoyed by native birds, providing valuable sources of food and shelter. The Japanese white eye, a small silver-eye-type bird, is an invasive bird species in Hawaii, but its introduction means several native plants are now being pollinated, something that became a problem after the indigenous birds that used to pollinate the flowers became extinct.
Some places have taken the invasion biology approach to conservation to heart. In New Zealand, much of the conservation movement is aimed at the removal of non-indigenous species in an attempt to recreate uninhabited areas that appear to present a more “nativist” landscape. Even in towns and cities, there is a strong drive to exterminate wild mammals (before Man arrived, New Zealand had no mammals other than bats), and many public parks and private gardens are planted predominately—sometimes exclusively—in native plants. The Department of Conservation has a long list of “weed” species under the [usually chemical] gun, and every Kiwi is deliberately indoctrinated to believe that rats, stoats, possums, and feral cats are public enemy number one (two, three, four…). New Zealand has become a land of poisons and traps for unwary four-foots. It is a profitable industry. (For more on this, see my blog posts Predator Free New Zealand and How Belief About the Nature of Nature Impacts Conservation Decisions.)
One of the primary arguments presented by invasion biologist enthusiasts, especially in places like New Zealand, is that controlling or exterminating invasive species in an ecosystem helps improve biodiversity. See my previous post on biodiversity for a bit more on that issue.
Certainly, studying the effects invasive species have on an ecosystem and its inhabitants provides tremendous opportunities for understanding how ecosystems function. While much of the current movement is directed towards removing visible species identified as “pests,” I think much could be gained in simply observing what Nature does without human interference. It can be argued that Man, rather than Nature, is responsible for moving species out of their native habitats and into alien ecosystems, and therefore He has a responsibility to remedy those “mistakes”. Yet, once established in the new ecosystem, invasive species become a part of that system, and their removal results in yet more chaos for Nature to repair.
There is a lot we don’t know. We are just beginning to understand and appreciate the interconnections between individuals and species. In spite of Darwin’s theory that species thrive through competition and that only the fittest will survive, we are beginning to understand that many species have symbiotic relationships with other species, some species are surprisingly nurturing to others, and that when one thing is changed in a system, many things change.