This article is an assigned reading from my extinction and climate change course - how awesome is that?
Chronicle Of Higher Education, August 16, 2002 Are You a Lumper or a Splitter?
By MALCOLM G. SCULLY
Michael A. Mares, director of the Sam Noble Oklahoma Museum of Natural History at the University of Oklahoma, puts it bluntly: "If you don't know the taxonomy, you know nothing." In A Desert Calling: Life in a Forbidding Landscape, published this year by Harvard University Press, Mares adds, "Not to understand how a species differs from a closely related species is ... to be ignorant at a most fundamental and profound level about all aspects of the biology of the species, its populations, the community of interacting species, and the ecological system in which they function." Few biologists would disagree, in principle, but, as Mares acknowledges, answering the question of what constitutes a "good" species has long been a confusing and controversial exercise, especially in parts of the world that have not been studied extensively. Knowing exactly when a population of creatures differs enough from similar populations to qualify as a separate species is no simple matter. Yet the issue of getting species "right" has taken on growing importance as concern has grown over such issues as identifying and protecting the world's biodiversity, developing conservation programs, and adopting policies, such as the Endangered Species Act, to prevent extinctions.
The issue is especially difficult in ornithology, where the differing and sometimes competing interests of hobbyists, environmentalists, systematists, and evolutionary biologists, among others, have triggered confusion and contention. As Clemencia Rodner, president of the Venezuelan Audubon Society, says in a recent message on an e-mail list for people interested in neotropical birds, "The taxonomy of South American birds has been in turmoil for a number of years now. It requires no crystal ball to predict that it will continue to be in that agitated state for many more years to come." There are, she adds, "many tacit agendas that run as undercurrents affecting taxonomic discussions. ... I have observed politics (both national and institutional), patriotic sentiments, birding-guiding, xenophobia, prestige, paranoia, ambition, egotism, lack of professional ethics, dismissal of scientific methods, and plain old stupidity get in the way."
The debate in ornithology has often been described as being between lumpers and splitters, between those who group separate but very similar populations of birds into a single species and those who divide such populations into full species. Generally, the lumpers employ what is known as the biological species concept, which until recently was the dominant taxonomic approach. Its proponents define a species was a group that is reproductively isolated from other groups, which means, as Douglas J. Futuyma, an evolutionary biologist at the State University of New York at Stony Brook, explains, that "two groups do not substantially exchange genes in nature, because of 'biological' differences that prevent gene exchange."
Many splitters use the increasingly popular phylogenetic species concept, which, as described by Joel Cracraft, curator of the department of ornithology at the American Museum of Natural History, defines a species as a "diagnosable" population, "among which there is a pattern of ancestry and descent." Futuyma adds that a phylogenetic species is "any population in which most members share a distinctive feature of any kind that distinguishes it from other populations."
The divisions aren't simply a matter of scientific disagreement. For one thing, avid birders who compete to see the largest numbers of species get an automatic addition to their life lists -- "an armchair tick" -- if they have seen individual birds from two populations that are subsequently split into different species. In one case, they could add as many as five more species without leaving home: Under the phylogenetic approach, geographically separated populations of the purple swamphen, a coot-like bird found in subtropical and tropical areas, have been split into six species. Such splits have been characterized as "tournithology" -- because they create new targets for birders willing to travel the world in search of new species for their life lists.
While birders and systematists have their own preferences in determining what constitutes a species, the "species problem" may become an increasingly political issue in debates over how best to protect biodiversity. Many environmentalists fear that confusion spawned by disagreements over the issue will give governments and developers an excuse to move ahead with plans and programs that could reduce biodiversity before we can even agree on how much of it there is.
As Rodner says in her message, "The real battle is not between splitters and nonsplitters. It is between our capacity to complete the task of identifying/defining the continent's avian fauna and the capacity of governments to allow and even promote its destruction." Especially in South America and Southeast Asia, she adds in a later e-mail message, the need to collect and study species is urgent. We still don't know all the animals we have in the world, she says, "and yet we are erasing miles and miles of habitat, and with them scores and scores of animals with every passing day." James Van Remsen Jr., curator of birds at the Louisiana State University Museum of Natural Science, warns as well that conservation biology will face major credibility issues "if anti-conservation people pick up the scent that a new concept is being adopted as a ploy to elevate more taxa to species level." "Taxonomic decisions need to be divorced entirely from conservation issues, or risk being devalued," Remsen says. Taxonomic problems arise, in part, because evolution is a process whereas a classification is a snapshot of that process at a moment in time.
The late ornithologist Charles G. Sibley wrote in 1996, "Evolution produces all degrees of genetic differences between populations of organisms, but, for practical reasons, we must limit the number of degrees we choose to 'recognize' by names. We assign names of populations and proposed definitions of
taxonomic categories based on various criteria, but the 'species concept' is slippery because there are so many examples in nature of populations that refuse to fit our limited set of definitions and names." Sibley himself was one of the fomenters of a controversial revolution in avian taxonomy. He and a colleague, Jon E. Ahlquist, used a process known as DNA-DNA hybridization -- in which strands of DNA from different species are bound together and compared -- to determine the relationships of the various families of birds. The results, published in 1990, shook up conventional taxonomies and drew both admiration and derision. From their studies they concluded that many earlier classifications of the relationships of bird families were wrong. For instance, they said that vultures found in North and South America were more closely related to storks than to Old World vultures, and that loons and grebes, which many
taxonomists had argued were closely related, weren't.
Sibley and Ahlquist's work remains controversial and has not been widely accepted, but many people believe that eventually DNA studies will resolve many of the most vexing taxonomic issues. Louisiana State's Remsen notes, however, that genetic-based approaches work best at the "higher and middle taxonomic levels" -- in establishing how closely families, genera, and species are related to each other. Molecular techniques are less useful, he adds, when you're trying to decide whether distinctive populations of similar birds should be lumped or split. "What molecular data can give you is an approximation of how different" the genes of two isolated populations are, he says, "but how you interpret those differences is basically arbitrary. "How different do they have to be genetically before you call them two species? It's arbitrary, as arbitrary as any decision made in any species concept." Even if molecular techniques can resolve many issues, Rodner notes, that day has not yet arrived. Systematists still need to collect and study specimens, and ornithologists need to learn as much as they can about the behavior, range, vocalizations, and other characteristics of bird populations. Sibley also acknowledged that the changing taxonomic approaches could look like little more than a game to outsiders. "But there is serious science in this process," he added, "because we are trying to fit nature into a system to improve our understanding of the processes and products of evolution, yet nature is complex and often resists our
Over the years, those efforts to fit birds into a system have resulted in a growing number of species. In 1951 Ernst Mayr and Dean Amadon published a world list that totaled 8,590. By 1996, when Sibley and Burt Monroe published their own list, the total had risen to 9,946 known species. The discovery of previously unknown species -- primarily in South America and Asia -- accounted for a small part of that increase, but the large majority came from the reclassification of subspecies as species. And with the growing popularity of the phylogenetic species concept the numbers could soar. Edward O. Wilson, in his recent The Future of Life (Alfred A. Knopf, 2002), says, "It is not out of the question that the number of validated living bird species will eventually double, to twenty thousand." And doubling the number of species would probably double the
number needing protection as well.