The main theories of biodiversity either neglect species interactions1, 2 or assume that species interact randomly with each other3, 4. However, recent empirical work has revealed that ecological networks are highly structured5, 6, 7, and the lack of a theory that takes into account the structure of interactions precludes further assessment of the implications of such network patterns for biodiversity. Here we use a combination of analytical and empirical approaches to quantify the influence of network architecture on the number of coexisting species. As a case study we consider mutualistic networks between plants and their animal pollinators or seed dispersers5, 8, 9, 10, 11. These networks have been found to be highly nested5, with the more specialist species interacting only with proper subsets of the species that interact with the more generalist. We show that nestedness reduces effective interspecific competition and enhances the number of coexisting species. Furthermore, we show that a nested network will naturally emerge if new species are more likely to enter the community where they have minimal competitive load. Nested networks seem to occur in many biological and social contexts12, 13, 14, suggesting that our results are relevant in a wide range of fields.

This policy summary looks at reported and possible, future consequences of climate change in the greater Himalayan region. The main emphasis is on responses in high mountain phenomena like glaciers, permafrost, and avalanches; the implications for water resources, ecosystems, and hazards; and how these threaten regional populations. The assessment points to a serious need to improve relevant knowledge in the region concerting key policy areas and strategies to improve the adaptive capacities of communities at risk.

You might not have thought about the importance of filling your coffee cup with Free Trade Certified java, but the decision you make about where to spend your money can have far-reaching consequences.