Invasions created the Mara, Serengetti vista
From ANIMAL PEOPLE, March 2000
KEEKORAK, Kenya––The Masai Mara National Park in southwestern Kenya and the Serengetti National Park of northwestern Tanzania together offer one of the world’s great wildlife viewing venues, punctuated by the spring and fall migrations of the wildebeests, in herds of thousands.
Yet if the bioxenophobes who dominate the conservation establishment were philosophically consistent, the great wildlife parks would represent an ecological horror show: almost all of the charismatic megafauna whom the world beats paths to see were once invasive species.
Elephants would be especially reviled––as they are, by many botanists––because their habit of breaking down trees tends to keep the savannah from evolving back into the dry forest it apparently was once, before they came.
Humans, ironically, are native to Kenya. Our earliest traces continue to emerge in astonishing bits and pieces from the Olduvai Gorge and elsewhere in the Rift Valley, just to the north. It was apparently from Kenya that humans spread, as the most successful of all large invasive species, following a well-beaten track. The subcontinent of India broke away from Africa circa 50 million years ago, transporting the entire Kenyan and Tanzanian ecology––as it then existed––to Asia.
In relative geographic isolation, African lions evolved into Asiatic lions; cape buffalo became water buffalo; topi became nilgai; green vervets differentiated into Hanuman languors; mongooses split into numerous African and Asian species; and jackals found their way north, over the Beringian land bridge from Siberia to Alaska, opposite to the direction of elephant and zebra migration, to become coyotes.
This natural activity differed in effect from modern species translocation and re-establishment in new habitats chiefly in that it happened slowly, before our time.
Without question, human mobility and the human penchant for taking other species along have greatly accelerated the movement of animals and plants from habitat to habitat–– but it is unlikely that the speed of movement has meant much in terms of the ability of newcomers to take over anywhere.
Whether it takes millions of years or just a few months for an “invasive” species to discover an accessible niche, the purported conquest proceeds in much the same manner. The takeover is only as rapid as the established species allow, as the newcomer breeds up to the carrying capacity of the new habitat, adapting to differing climatic conditions and learning to cope with new adversaries.
“Conquest” and “takeover” are the terms humans tend to apply to “invasive” species, but are not very accurate metaphors, since they tend to reflect the behavior of would-be dominant individuals within a species more than species interaction. Humans conquer humans; male impalas win harems by conquering rival males; and females may be said to make conquests of males, too, albeit more by stratagem than direct test of strength. In species-against-species conflict over habitat, however, dominance is determined less by direct conflict than by the weather, which tends to govern the abundance of food, the fecundity of mothers, the arrival of other newcomers, and the security of nests against wind, fire, flood, and drought.
Native species always have a huge natural advantage, in having evolved to cope with the prevailing conditions in a particular place. A well-established native species is rarely at risk from newcomers––unless the habitat has already changed so that the environment the species now occupies is no longer the habitat it evolved to occupy.
Then, in effect, the native species is no longer “native” in the sense of being well-adapted. Instead, adaptations to the habitat as it was may leave the native species maladapted, likely to recede to the least changed habitat fragments, and perhaps become extinct, whether or not any other species “invade” to “take over.”
Closer study shows that alleged “invasive” species which have supposedly crowded native species to the edge of extinction are not so much conquerors as opportunists, moving into vacant houses and recycling the remnant furnishings.
The Kenyan wildlife parks offer one of the most easily observable examples of the longterm effects of “invasion.”
Commonly portrayed as examples of a “timeless” ecology, in which species continue to interact in a semi-harmony established during the Pleistocene epoch, the Masai Mara, Amboseli, Tsavo et al are actually examples of remnant ecology stacked on remnant ecology.
Visitors on a photo safari see remnants from almost every epoch of evolution: from bluebacked lizards who probably were there before the dinosaurs; to ostrichs, spur fowl, and secretary birds who most likely coexisted with the dinosaurs, long before the Rift Valley itself formed; to the Pleistocene-vintage elephants, rhinos, and ungulates ranging in size from the diminutive dik dik to the elk-like waterbucks. The horse-like zebras may have come almost last, having evidently arrived after India separated from Africa.
Among the large mammals, only humans are likely to have emerged later––and only humans may be truly “native” in the sense that bioxenophobes tend to use the term, meaning that they first appeared in the land that is now Kenya.
Bioxeonophobic logic, as applied in the current global effort to eliminate “invasive” species worldwide, would thus require extirpating elephants and zebras from Kenya, in favor of expanded human habitation.