Effects of global regions and international systems

Environment

Lake Victoria is a natural body of water that has experienced exponential change within the past hundred years due to human activity. Even before the twentieth century, however, some experts suggest that it was home to one of the most explosive and fascinating demonstrations of evolution in the history of life. In the relatively short geologic time that the lake has existed, it has become home to numerous species of cichlid fishes of extraordinary variation. Though the actual number of haplochromine species that came to inhabit the lake remains in debate, what is apparent is that the species that do exist stand poised to tell an evolutionary story that could shed light upon many aspects of evolutionary theory.

Still, how scientists will uncover this story is becoming increasingly hazy, as the natural environment of these fishes is being irreversibly changed. Applying the biological definition of a species may be fundamentally useless as observing cichlids in the wild becomes ever more unfeasible. As a result, genetic research on captive populations of the fish may be the best way to identify the specific mechanisms that brought about the cichlid adaptive radiation in Lake Victoria, while morphological analysis should accompany these findings with observations of current distinctions. Centrally, this research must be performed on the current captive populations of cichlids, since the environmental factors that brought them into existence no-longer exist.

Understanding how to categorize species in general is essential to research efforts in Lake Victoria. The Endangered Species Act, for example, takes a rather vague perspective regarding its definition of species: "Species' is defined in the ESA as including a species, a subspecies, or, for vertebrates only, a distinct population segment (DPS)." Such an interpretation of what a species is leaves ample room for debate concerning precisely what populations of animals are to be preserved. Accordingly, the effects of invasive species, depending upon one's interpretation of what a species is, could be depleting thousands of endemic species or only a handful. There are few places in the world in which this issue is more pertinent than in Lake Victoria, where the count of native cichlid species has run, according to experts, from merely five to over four-hundred. Additionally, decisively deciding what the species count should be is central to the efforts of counteracting the negative influences of the nonnative Nile perch.

In short, Lake Victoria is a special case. It is a very young lake -- perhaps only 12,000 years old -- but it is also reasonably isolated from nearby aquatic ecosystems. As a result, "All of the Lake Victoria cichlids appear to have descended from a single ancestral species that colonized Lake Victoria from nearby older lakes." This feature of Lake Victoria makes the issue of conservation even more important to those studying evolution. Since the East African lakes' ages vary so widely, and it is believed that many of them have remained isolated for millennia, "This provides a unique opportunity for comparison: cichlid radiations can be observed at different 'stages' of evolution, in this case, as living organisms." So, the sort of value that can be placed upon the biologic variation in Lake Victoria reaches beyond merely the categorizing of species and subspecies; the cichlid variations are valuable as a whole because they offer a concrete example of adaptive radiation. Put differently, the current conservation laws, which only protect species or distinct populations, fail to neatly apply to a situation in which preserving an entire spectrum of adaptation may be scientifically significant.

Yet, despite the intrinsic value of the lake to scientists, its more tangible economic and social value has contributed to the drastic changes it has undergone in the past century. Lake Victoria is a vital source of fish and water for the surrounding human populations and this, certainly, must take precedence over any influences that might harm fish. However, "Eutrophication (mainly from changes in land use) and non-indigenous fishes and plants have changed Lake Victoria from a clear, well-oxygenated lake with incredible diversity of cichlid fishes (dominated by planktivorous, herbivorous, and benthivorous species), to a murky, oxygen-deprived, weed-choked lake with diminished fish diversity (dominated by predators)." Goldschmidt notes that the human population in the Lake Victoria basin is growing at an annual rate of 3 to 4%, and the deforestation rate is currently increasing 1 to 2% annually. As a result of the associated land use alterations to the basin, eutrophication began to drastically decrease the oxygen levels in the lake in the early portion of the twentieth century. This means that today "at least 30% of the lake bottom is often without oxygen. Thus, less of the lake is available to fish and other organisms." Not surprisingly, the associated ecological changes have acted to eliminate many native fish species.

Furthermore, it would seem, these environmental changes have accelerated the destruction of cichlid fishes because of the strains they have put on the surrounding human economy. As the two most fished native species began to falter from over fishing and habitat destruction, people were forced to introduce nonnative species into the ecosystem in the 1950s; these species included two non-indigenous tilapia species as well as Nile perch which "were stocked to convert the substantial biomass of smaller fish into large fish suitable for large-scale, higher capital investment and exploitation for human consumption." Although this was almost certainly beneficial to the surrounding economy -- in fact, between 1981 and 1989 the tonnage of fish caught in the lake, annually, increased by almost 800% -- the native cichlid fish were devastated. Also, the depletion of oxygen was further quickened due to a decrease in herbivorous fishes; this has caused an explosion of algae and hyancinth. and, like a domino effect, the abundance of these weeds has made it currently difficult to navigate across Lake Victoria, and has even fostered the emergence of disease-causing snails and mosquitoes. Overall, "Not only has the unparalleled species flock of cichlids been imperiled, but the ability of the lake to meet human needs is now threatened."

Judging from these pressures, it appears almost as if the cichlid fishes of Lake Victoria are inevitably doomed. To this point in the history of human involvement in the lake, virtually every action intended to improve it has backfired. In this way, Lake Victoria tends to typify the bind that modern conservationists face: not only are they limited by the particular organization of conservation laws, but they are hindered by the demands of human economies and the dismal track record of scientists who have attempted to find biologic solutions for ecological problems. Just as the introduction of disease into the population of European rabbits in Australia only served to deplete their numbers for a handful of generations; it is unclear that continuing the practice of bringing non-indigenous species of plants, animals or microbes to Lake Victoria could accomplish anything more than complicating the problem.

Nevertheless, it is reasonable to wonder why we should care. After all, it is highly likely that the negative economic implications of eutrophication and nonnative species can be overcome by introducing new plants and animals to the environment; however, it is very unlikely that such practices could ever ensure the survival of the cichlids. The justification for preserving the species of cichlids in Lake Victoria is somewhat more abstract. Edward O. Wilson writes, "Natural history becomes all the more pleasing and interesting when we look at it through the lens of evolutionary theory and search for the starbursts of adaptive radiation -- and all the more foreboding when we learn how quickly these creations can be extinguished." With this in mind, the cichlid fishes of Lake Victoria must be worthwhile from a utilitarian standpoint because they possess the capacity to provide us with new and useful knowledge. The very fact that categorizing them has become difficult and contentious must be a symptom of the overall mystery of evolutionary theory -- they are an enormous blob drawn on the tree of life. But this blob is rapidly being erased; so understanding as much as we can about it now is, perhaps, the best avenue towards avoiding such negative ecological impacts in the future, and towards slowing the rate at which the cichlid blob disappears.

There are many features of the cichlid population of Lake Victoria that make it very significant. DNA research performed by Axel Meyer and his colleagues in 1990 "calculated that the full cichlid evolution was achieved in no more than 200,000 years." This suggests that the cichlids neatly satisfy the criteria for what Wilson calls "species flocks"; essentially, these are groups of organisms that have "relatively numerous species of immediate common ancestry and are limited to a single well-isolated area such as a lake, river basin, island, or mountain range." Adding to the significance of the cichlids is that Lake Victoria appears to possess very few natural barriers, which might otherwise explain why 300 species -- according to Wilson -- could arise in so short a period of time. The geographic layout of Lake Victoria suggests that they speciate by sympatric means. Still, it is not unimaginable, within a lake as large as Victoria that they might also divide into separate populations along very subtle lines of variation -- like mating behaviors or feeding preferences.

This sort of interpretation of the situation in Lake Victoria, however, rests upon the notion that the species of cichlid found there evolved from a single ancestral species. Yet, even Meyer acknowledges that this might not be the case: "Within the past decade, however, morphology has increasingly emphasized the view that the flock may be polyphyletic." Put differently, it is possible that the species of cichlid that have evolved in Lake Victoria came from a group of distinct, but closely related, fish that colonized the region several thousand years ago. If this is the case, then the scientific importance of the Victorian cichlids would be somewhat diminished, because a less explosive series of adaptive radiations could explain their modern occurrence.