College Basketball Study Tests a
Landmark Theory of Biodiversity
What does a court full of towering collegiate basketball players have in common with a forest full of vertiginous trees?
For legions of basketball fans, the answer may not go beyond height. But for ecologists who study species dynamics, the answer promises to alter our understanding of the success of species. It could also help better guide how conservation is practiced in an era of fast-multiplying extinctions.
In a study published on March 9 in PLoS ONE, a team of four ecologists at F&ES outlined a connection between basketball and ecology that is, at first glance, deceptively simple. They concluded that the pattern of wins and losses by basketball teams is essentially identical to how species flourish or fail in nature.
Straightforward as these similar distribution patterns may seem, the findings bring into question a landmark theory of species dynamics known as the unified neutral theory of biodiversity.
Developed in recent decades, neutral theory offers ecologists a tantalizingly powerful tool. As a statistical approach, it suggests that for any species—from trees to fish to microbes—patterns of diversity can be modeled solely on the basis of random fluctuations in births, deaths and new arrivals of species rather than on particular traits.
For many ecologists, the implications are jarring. By this reasoning, competitive aspects—whether drought tolerance in trees or poisonous glands in frogs—have little to do with a species’ long-term success relative to its competitors.
As a test of neutral theory, however, the basketball study proves otherwise, says Robert Warren, lead author of the study and a postdoctoral researcher at F&ES. “Some scientists say that the theory of survival of the fittest predicts which species are abundant; some say it is just random,” says Warren.
Scientists cannot assume that because “a mathematical model is simple, the underlying processes are simple,” says Warren. “This assumption is where unified neutral theory becomes problematic.”
To understand the allure of the neutral theory of biodiversity, it’s helpful to take a step back. Compared with physics or math, ecology has relatively few grand unified theories—as yet, there’s no E = MC2 to describe species dynamics.
Unlike more theoretical, mathematical sciences or experiment-based laboratory studies, field biology is messy. Collecting observational data on flora and fauna in their habitats is painstaking. And the data sets from studying trees for decades, for example, are relatively small.
The upshot is that sweeping laws are notoriously difficult to make foolproof in ecology and, so, are rare.
The best-known example of such an insight is, of course, Charles Darwin’s quest to develop and refine his theories of natural selection to explain the process and history of the evolution of species that he observed in a mix of living animals and related fossil records.
In 1859, following decades of observation, he noted that “… rarity is the attribute of vast numbers of species in all classes …” in his landmark On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.
That’s why, in 2001, when ecologist Stephen Hubbell published a statistical explanation of the diversity and relative abundance of species in ecological communities, it caused such a stir.
Using statistical methods to assess tree populations in a tropical forest, Hubbell suggested that biodiversity derives from randomness more than from species-by-species attributes.
Put another way, variables such as species dominance, food supply, climate or competition can be treated as neutral, or ignored, in predicting a species’ success. For its methodological elegance, Hubbell’s 2001 book, The Unified Neutral Theory of Biodiversity and Biogeography, changed the paradigm for the way ecologists modeled ecosystems.
“It had long been assumed that competition and the theory of survival of the fittest created the diversity patterns observed in nature as species evolved unique niches to coexist,” says Warren. “Then unified neutral theory came along; it could explain species abundance as well, or better, than competition models.”
The theory set up a troubling dilemma, however, fueling a debate that has simmered ever since. As correct as the math of Hubbell’s unified neutral theory may be, it suggests that factors ecologists had long toiled to map and understand didn’t matter in the success or failure of a given species.
Ecology is a field where careers can be spent—as Darwin did sailing the seas—in remote study, meticulously assessing the effects of geography, environment or competitors on species. Against this backdrop, the implication of unified neutral theory suggests that, on average, none of these factors matter much more than any other—i.e., they are all neutral.
And while Hubbell didn’t necessarily intend for his study to guide conservation thinking, it nevertheless has big implications there, too.
On one hand, it offered a new tool: since unified theory mathematically combines the study of species abundance and biogeography—or how the distribution of organisms relates to the Earth’s physical features—it offers conservationists a tool to guide the sizing of reserves to harbor the greatest diversity of species.
But on the other hand, if competitive factors are truly neutral, then decisions made by conservation biologists about how best to protect a struggling species could easily be off target or even, at worst, a waste of time and money.
“Neutral theory would say just roll your dice,” says Oswald Schmitz, a co-author and Oastler Professor of Population and Community Ecology at F&ES. “But if there are rules about how species associate themselves on the landscape and there are mechanisms behind the rules, then that has very different management implications than a neutral-theory approach.”