The more the merrier

Abstract

The 'nested' pattern of mutualistic interactions between plants and their pollinators is thought to promote species coexistence. But the key determinant may instead be the number of partners that species have. See Letter p.227 The nested structure of mutualistic ecological networks — the tendency for ecological specialists to interact with a subset of species that also interact with more generalist species — is thought to promote biodiversity. This study of 59 empirical data sets for plant-pollinator mutualisms comes to the surprising conclusion that adding mutualisms typically decreases biodiversity by breaking the competition symmetry, and that nestedness is not important in determining ecosystem function. According to this model, it is the simpler measure of the number of mutualistic links a species has that determines its survival chances, with nestedness being just a side effect.