in the rate of reproduction that tips a population over the point from which it cannot recover. It was at this time that Jim Brown set about looking for some other way to explain diversity besides competition. Other ecologists spoke of their discipline as being “in crisis,” “repugnantly complicated,” and “in a quagmire.”
French wine makers have a concept called terroir, meaning each vineyard’s unique combination of soil, climate, and geography. The idea is heavy with mystique, and the link between terroir and a wine’s flavor is held to be inexplicable and impossible to unpick. Perhaps biodiversity comes about as the result of some sort of ecological terroir, with the number and type of species in a place being due to idiosyncratic local conditions interacting in unfathomably complex ways. Perhaps, although species obviously occupy different niches, the search for generalities is misguided, and the niche is a sterile mathematical concept that cannot be measured in the real world. But many ecologists think not, and for them competition and the niche are alive and well.
Some ideas still focus on how competing species apportion resources. In 1976, David Tilman, then a Ph.D. student at the University of Michigan, found that two species of algae could share Lake Michigan because they differed in their ability to use phosphorus and silicon. One species was especially good at getting phosphorus out of the water and so could thrive in a low-phosphorous environment. But it needed lots of silicon, which the other species was better at obtaining. Each had traded off its competitive abilities in one arena against its competence in another, and, as long as silicon and phosphorus were spread unevenly, both could coexist. Since then, Tilman and his colleagues have developed this idea into a more general theory, particularly applicable to plants, which argues that each species is a specialist for a certain set of conditions. Every point in niche space becomes a potential niche—again, the potential number of coexisting species is limitless. Species thrive in some places and wither in others, but because environments are variable many species can share a place.