All plant species need light, water, and nutrients to survive, so you might expect that the fiercest competitors for these resources would dominate habitats everywhere. Yet ecosystems harbor a dazzling diversity of species. In the current issue of Nature, researchers present data backing a theory that explains this so-called "diversity paradox."
One of the most popular explanations for species abundance holds that seemingly homogeneous habitats consist of many niches. To conquer a niche, plants will specialize to exploit miniscule differences in everything from temperature and humidity to amount of shade and soil type. But obtaining evidence for this theory has been hard.
To tackle the problem, ecologist Jonathan Silvertown and his colleagues from Open University in Milton Keynes, United Kingdom, took an inventory of all the plant species in two English meadows. They used a model based on 15 years of local water data to map soil moisture in the meadows, and overlaid that with a map of vegetation. They discovered that each species had adapted to a narrow range of moisture conditions.
The findings suggest that "species are able to use different parts of these sites to gain a competitive edge," says James Grace, an ecologist at the National Wetlands Research Center in Lafayette, Louisiana. David Tilman, an ecologist at the University of Minnesota in Minneapolis agrees, but cautions that mininiches seen in the meadows may not explain species richness in other habitats. "I predict there will be a diversity of theories that explain diversity," he says.