Elton, C S. The Ecology of Invasions by Animals and Plants. New York: Methuen, 1958.
This intelligently written and accessible (can there be one without the other?) work was published some time ago by an Oxford ecology professor and immediately recognized as a pioneering effort to chart the remarkable series of opportunities humans have given other species to invade and colonize new ecosystems. Through commerce, war and pilgrimage—via triremes, galleys, steamships, railroads and jumbo jets—adaptable organisms have taken advantage of humanity’s ignorance, indifference, or carelessness to move into alien territory. The reasons for the success or failure of various organisms to take root in foreign soil is explored in depth by the author, and the mass extinctions caused by the purposeful or accidental introduction of exotic species are given a thorough examination and appraisal.
It is clear from Dr. Elton’s study that if Homo sapiens is the most recent species to subject other organisms to genocide he is certainly not the first. Invasion and usurpation of isolated ecosystems has been a matter of course throughout life’s history; however, along with the accelerated rate of species extinction and the sly rising of the planet’s temperature, the phenomenon of ecological disruption by alien invaders has been greatly acerbated by the rise and restless mobility of industrial society. Elton speaks of some species “exploding” on a new landscape, spreading with remarkable rapidity throughout the interior, colonizing various ecological niches to the exclusion of less aggressive or outnumbered natives. Generally these huge successes for the exotic species have taken place in ecosystems such as islands, biogeographically isolated for millennia, with the indigenous species having become overspecialized and evolutionally “decadent” over a long history of living in unchallenged largess. (More recent experience, with, e.g., the Ebola virus, demonstrates that similar outbreaks can be occasioned by anthropogenic disruption of ancient undisturbed ecosystems.)
The invasion of exotic species can be insidious. Many of the animals and plants we take for granted here in the United States are, like many of us, ultimately of foreign origin. Various mammals, birds, fishes and plants were purposefully introduced here, for reasons spanning the economic to the pseudoscientific, up to and including the dim realm of inspired idiocy. Some of the more successful colonists include the Prussian boar (hybridized with escaped domestic swine) of Appalachia, the English “sparrow” (actually an Old World weaver finch), the despised European starling (Sturnus vulgaris), the rock dove (common pigeon), the brown trout, grass carp, ring-necked pheasant, Eurasian chukar, the Mongolian thistle (tumbleweed), water hyacinth, and the creeping kudzu vine. Of all of these purposeful introductions, only the pheasant can be said to have had a comparatively low negative impact on North American wildlife. Other exotics were not as kind to their adopted land; the starling, for example, first released by a man in Central Park who wanted all of the animals listed in Shakespeare’s plays to join him in the New World, has truly exploded in its advance across the continent, driving out native avifauna like the eastern bluebird and various other cavity dwellers along the way to become, today, our second most populous American bird (after, amazingly enough, the native mourning dove).
Other American introductions were, thankfully, not so prosperous. These include well-meaning attempts by presumably intelligent men and women to bless our land with numerous exotic game animals (the African kudu and the Asian sitka deer to name two), along with parrots, skylarks, linnets, ferrets, piranhas, monkeys, ostriches, elephants and camels. (Legend has it that Henry Hudson brought an elephant with him on his exploration of the river system that bears his name, as a gift to the hypothetical King of the Indies; overly troublesome to maintain, the animal was allegedly released somewhere in the region of present day Poughkeepsie, New York.)
Accidental and/or escaped species brought from overseas include the highly destructive feral house cat, the European house mouse, the Norway and black rats (whose fleas harbored the Black Death), the zebra mussel, gypsy moth, Japanese beetle, Dutch elm disease, chestnut blight, sudden oak death syndrome (the last three being exotic fungal infections of native trees). The unfortunate list must also include smallpox, measles, tuberculosis, and hosts of other stowaway legacies from the Old World which served to break American Indian resistance to European invasion.
The economic and ecological consequences of unwise or unplanned introductions is becoming increasingly felt throughout the planet, so much so that the author, almost fifty years ago, felt compelled to prophetically warn that “we are faced with a life-and-death need not just to find new technological means of suppressing this plant or that animal, but of rethinking and remodeling and rearranging much of the landscape of the world that had already been so much knocked about and modified by man, while at the same time preserving what we can of real wilderness containing rich natural communities.”
Dealing with destructive exotics has since become a high priority for US agricultural, customs, and wildlife personnel. Dr Elton describes the control of exotics as being approached in a triage fashion: initially, quarantine of foreign ships, cargo, vehicles and baggage is used to determine the presence of alien species. If a small foothold in the potential host country is established, the exotic community may be surrounded and eradicated by whatever means necessary (as was the African malaria mosquito in Brazil during the 1930s); this procedure, due to the typically small size and mighty reproductive powers of, say, insects, is generally impossible on a large scale. Finally, if an exotic has populated a large area, control is the remaining option, meant to keep the invader’s numbers in some kind of bounds. (This is sometimes accomplished with winter roosts of European starlings, to the sick delight of some, by the spraying of detergent from municipal firehoses onto the close-packed sleeping birds; the soap soaks in and strips the feathers of insulating oils, and the winter cold does the rest.)
Dr Elton has few illusions about the permanence of control measures for most exotic species, and lists several instances where invaders have seriously disrupted native ecosystems, mainly fragile islands, from trees snakes in Guam to mongooses in Hawaii. Following the hallmark of a great scientist, however, Elton has as much love for as understanding of the ecosystems under study. He also finds humor in his generally grim work, recalling that upon being introduced to the European human flea, “the placid natives of Aitutaki [a small Pacific island], observing that the little creatures were constantly restless and inquisitive, and even at times irritating, drew the reasonable inference that they were the souls of deceased white men.”
This intelligently written and accessible (can there be one without the other?) work was published some time ago by an Oxford ecology professor and immediately recognized as a pioneering effort to chart the remarkable series of opportunities humans have given other species to invade and colonize new ecosystems. Through commerce, war and pilgrimage—via triremes, galleys, steamships, railroads and jumbo jets—adaptable organisms have taken advantage of humanity’s ignorance, indifference, or carelessness to move into alien territory. The reasons for the success or failure of various organisms to take root in foreign soil is explored in depth by the author, and the mass extinctions caused by the purposeful or accidental introduction of exotic species are given a thorough examination and appraisal.
It is clear from Dr. Elton’s study that if Homo sapiens is the most recent species to subject other organisms to genocide he is certainly not the first. Invasion and usurpation of isolated ecosystems has been a matter of course throughout life’s history; however, along with the accelerated rate of species extinction and the sly rising of the planet’s temperature, the phenomenon of ecological disruption by alien invaders has been greatly acerbated by the rise and restless mobility of industrial society. Elton speaks of some species “exploding” on a new landscape, spreading with remarkable rapidity throughout the interior, colonizing various ecological niches to the exclusion of less aggressive or outnumbered natives. Generally these huge successes for the exotic species have taken place in ecosystems such as islands, biogeographically isolated for millennia, with the indigenous species having become overspecialized and evolutionally “decadent” over a long history of living in unchallenged largess. (More recent experience, with, e.g., the Ebola virus, demonstrates that similar outbreaks can be occasioned by anthropogenic disruption of ancient undisturbed ecosystems.)
The invasion of exotic species can be insidious. Many of the animals and plants we take for granted here in the United States are, like many of us, ultimately of foreign origin. Various mammals, birds, fishes and plants were purposefully introduced here, for reasons spanning the economic to the pseudoscientific, up to and including the dim realm of inspired idiocy. Some of the more successful colonists include the Prussian boar (hybridized with escaped domestic swine) of Appalachia, the English “sparrow” (actually an Old World weaver finch), the despised European starling (Sturnus vulgaris), the rock dove (common pigeon), the brown trout, grass carp, ring-necked pheasant, Eurasian chukar, the Mongolian thistle (tumbleweed), water hyacinth, and the creeping kudzu vine. Of all of these purposeful introductions, only the pheasant can be said to have had a comparatively low negative impact on North American wildlife. Other exotics were not as kind to their adopted land; the starling, for example, first released by a man in Central Park who wanted all of the animals listed in Shakespeare’s plays to join him in the New World, has truly exploded in its advance across the continent, driving out native avifauna like the eastern bluebird and various other cavity dwellers along the way to become, today, our second most populous American bird (after, amazingly enough, the native mourning dove).
Other American introductions were, thankfully, not so prosperous. These include well-meaning attempts by presumably intelligent men and women to bless our land with numerous exotic game animals (the African kudu and the Asian sitka deer to name two), along with parrots, skylarks, linnets, ferrets, piranhas, monkeys, ostriches, elephants and camels. (Legend has it that Henry Hudson brought an elephant with him on his exploration of the river system that bears his name, as a gift to the hypothetical King of the Indies; overly troublesome to maintain, the animal was allegedly released somewhere in the region of present day Poughkeepsie, New York.)
Accidental and/or escaped species brought from overseas include the highly destructive feral house cat, the European house mouse, the Norway and black rats (whose fleas harbored the Black Death), the zebra mussel, gypsy moth, Japanese beetle, Dutch elm disease, chestnut blight, sudden oak death syndrome (the last three being exotic fungal infections of native trees). The unfortunate list must also include smallpox, measles, tuberculosis, and hosts of other stowaway legacies from the Old World which served to break American Indian resistance to European invasion.
The economic and ecological consequences of unwise or unplanned introductions is becoming increasingly felt throughout the planet, so much so that the author, almost fifty years ago, felt compelled to prophetically warn that “we are faced with a life-and-death need not just to find new technological means of suppressing this plant or that animal, but of rethinking and remodeling and rearranging much of the landscape of the world that had already been so much knocked about and modified by man, while at the same time preserving what we can of real wilderness containing rich natural communities.”
Dealing with destructive exotics has since become a high priority for US agricultural, customs, and wildlife personnel. Dr Elton describes the control of exotics as being approached in a triage fashion: initially, quarantine of foreign ships, cargo, vehicles and baggage is used to determine the presence of alien species. If a small foothold in the potential host country is established, the exotic community may be surrounded and eradicated by whatever means necessary (as was the African malaria mosquito in Brazil during the 1930s); this procedure, due to the typically small size and mighty reproductive powers of, say, insects, is generally impossible on a large scale. Finally, if an exotic has populated a large area, control is the remaining option, meant to keep the invader’s numbers in some kind of bounds. (This is sometimes accomplished with winter roosts of European starlings, to the sick delight of some, by the spraying of detergent from municipal firehoses onto the close-packed sleeping birds; the soap soaks in and strips the feathers of insulating oils, and the winter cold does the rest.)
Dr Elton has few illusions about the permanence of control measures for most exotic species, and lists several instances where invaders have seriously disrupted native ecosystems, mainly fragile islands, from trees snakes in Guam to mongooses in Hawaii. Following the hallmark of a great scientist, however, Elton has as much love for as understanding of the ecosystems under study. He also finds humor in his generally grim work, recalling that upon being introduced to the European human flea, “the placid natives of Aitutaki [a small Pacific island], observing that the little creatures were constantly restless and inquisitive, and even at times irritating, drew the reasonable inference that they were the souls of deceased white men.”
