Darwin’s entangled bank and the architecture of biodiversity

Jordi Bascompte

 Integrative Ecology Group, Estación Biológica de Doñana, CSIC, Sevilla, Spain

 Among his many research interests, Darwin was fascinated by the intimate interactions between orchids and their insect pollinators. In 1862, only three years after the publication of “The Origin of Species,” he published a new book entirely devoted to this topic. Since then, it is widely acknowledged that the mutualistic interactions between plants and the animals that pollinate them or disperse their fruits have molded the organization of Earth's biodiversity. Darwin also envisioned the “entangled bank” or complex web of interactions among species within an ecosystem. Recent work integrates these two major contributions by Darwin by considering that mutualistic interactions can form complex networks of species interdependencies. The complexity of these networks, involving hundreds of species, can be disentangled using tools from network theory. The emerging picture describes these coevolutionary networks as highly heterogeneous, nested, and built upon weak and asymmetric links among species. Such general architectural patterns seem to increase network robustness to random extinctions, and maximize the number of coexisting species. Therefore, mutualistic networks can be viewed as the architecture of biodiversity. However, because pylogenetically similar species tend to play similar roles in the network, extinction events trigger non-random coextinction cascades. This implies that taxonomic diversity is lost faster than expected if there was no relationship between phylogeny and network structure.

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