Monday, August 4, 2008 - 1:50 PM

COS 6-2: Towards a general theory for mutualistic networks

Ugo Bastolla1, Migel A. Fortuna2, Alberto Pascual-García1, Antonio Ferrera3, Bartolo Luque3, and Jordi Bascompte4. (1) Centro de Biología Molecular, (2) Estación Biológica de Doñana, CSIC, (3) Universidad Politécnica de Madrid, (4) Estación Biológica de Doñana


The mutually beneficial interactions between plants and their seed dispersers or pollinators create complex networks of mutual dependences involving dozens of species. These mutualistic networks are highly nested, with a core of reciprocal generalist species and a tail of specialists interacting asymmetrically with the most generalist species. Little is known, however, about the implications of nestedness for the persistence of biodiversity. Progress in that direction has been precluded by a lack of theory on species-rich facultative mutualisms such as the one existing for competition or predation.  Here we extend competition theory to analytically quantify the increase of biodiversity supported by nested mutualistic networks. Our approach is based on the previous result that in a purely competitive system, the largest eigenvalue of the competition matrix limits the maximum biodiversity that the system can attain. We apply our analytical predictions to a dataset of 56 communities.


Our results show that the nested structure of mutualistic networks enhances species biodiversity through a reduction in effective interspecific competition.