Non-random coextinctions in phylogenetically structured mutualistic networks

Plants and their pollinators and seed dispersers form complex networks of interdependences. These networks have a well-defined architecture that strongly affects biodiversity maintenance. Using a phylogenetic approach, Rezende et al. show that past evolutionary history of plants and animals partly explains the network patterns. Closely related species tend to play similar roles in the network. As a result, coextinction cascades following a species extinction affect taxonomically related species, resulting in a non-random pruning of the evolutionary tree. From a conservation standpoint, this means that cascades of coextinction may spread across related species, further increasing the erosion of taxonomic diversity. A phylogenetic approach is used to show that past evolutionary history partly explains network patterns that link plants and their pollinators and seed dispersers. Species close in the phylogeny tend to play similar roles in the network. As a result, co-extinction cascades following the extinction of a species affect taxonomically related species, resulting in a non-random pruning of the evolutionary tree. The interactions between plants and their animal pollinators and seed dispersers have moulded much of Earth’s biodiversity1,2,3. Recently, it has been shown that these mutually beneficial interactions form complex networks with a well-defined architecture that may contribute to biodiversity persistence4,5,6,7,8. Little is known, however, about which ecological and evolutionary processes generate these network patterns3,9. Here we use phylogenetic methods10,11 to show that the phylogenetic relationships of species predict the number of interactions they exhibit in more than one-third of the networks, and the identity of the species with which they interact in about half of the networks. As a consequence of the phylogenetic effects on interaction patterns, simulated extinction events tend to trigger coextinction cascades of related species. This results in a non-random pruning of the evolutionary tree12,13 and a more pronounced loss of taxonomic diversity than expected in the absence of a phylogenetic signal. Our results emphasize how the simultaneous consideration of phylogenetic information and network architecture can contribute to our understanding of the structure and fate of species-rich communities.