Santa Fe Institute, New Mexico
A theoretician ponders what physics has to offer ecology.
Many species are concentrated in biodiversity hot spots such as tropical rainforests and coral reefs. But our estimates of how many species these and other ecosystems contain are very rough. Conservation efforts and ecological theories would be better served by a more accurate picture.
Our best guesses come from empirical species–area relationships, which count the number of species observed as a function of geographical area. These relationships show sharp increases at local and continental scales, but slow growth at intermediate scales. Despite decades of study, ecologists have no clear explanation of this pattern’s origins or what causes deviations from it.
James O’Dwyer and Jessica Green at the University of Oregon in Eugene recently developed a spatially explicit stochastic model of species birth, death and dispersal that can be solved mathematically using techniques from quantum field theory (J. P. O’Dwyer and J. L. Green Ecol. Lett. 13, 87–95; 2010). Amazingly, the model predicts a species–area relationship that agrees with decades of empirical data, without including ecologically important factors such as body size, predation, habitat or climate.
The work both solves a long-standing mystery and exemplifies a good null model. Because the model includes only neutral mechanisms (birth, death and dispersal), deviations can be interpreted as evidence of non-neutral, ecologically significant processes. It also shows the value of shifting the focus from small-scale, context-dependent processes to large-scale neutral dynamics, a perspective more common in physics than biology.
The model and its shift in perspective could shed light on the immense, important and increasingly studied world of microbial ecologies, which is even more mysterious than those of rainforests and coral reefs.