Specialization and Rarity Predict Nonrandom Loss of Interactions from Mutualist Networks

Untangling the Web Interspecific interactions link species within complex trophic and nontrophic webs (see the Perspective by Lewinsohn and Cagnolo ). Theoretical work has suggested that certain characteristics of species, or even interactions, may predispose them to extinction from a network. Aizen et al. (p. 1486 ) provide empirical evidence that plant-pollinator interactions are lost nonrandomly following habitat reduction in isolated hills in the Argentine pampas. Some types of interaction were more vulnerable to disruption than others, particularly when the specialization of the interacting was high and when the interactions were infrequent. Stouffer et al. (p. 1489 ) applied network theory to predict the dynamical importance of species across different food webs. Characteristic three-node motifs were identified, and species were characterized according to the relative frequencies with which they occupied unique positions within the motifs. These relative frequencies and the dynamic importance of the motifs were then used to identify a species-level importance within a food web.