Neutral theory tested by birds

摘要

A continental-scale analysis of habitat and bird distribution in South America provides the latest challenge for neutral theory — a controversial idea in ecology about what determines the make-up of communities. How do different species end up living together in communities? Do they coexist only when each finds a different niche, or simply when they happen to disperse to the same habitable region? Debate over these questions intensified not long ago with the introduction of 'neutral theory", a stochastic theory of community properties whose predictions have proven stubbornly robust, despite its disregard of the niches that many ecologists hold dear. Writing in Proceedings of the National Academy of Sciences, however, Graves and Rahbek2 point out continental-scale patterns in the bird communities of South America that neutral theory may not be able to explain. The dominant view in ecology is that species live together in communities only when they differ from one another. Species competing for the same nutrient or food source cannot coexist because one species will always be more efficient than the others and will quickly drive the rest to extinction. Species that coexist must differ from one another in the resource they use most efficiently or in the environmental conditions to which they are best adapted — that is, they must have different niches. This view is often called 'niche-assembly'.