Topological key players in communities:: the network perspective

For both a general understanding of ecosystem functioning and the setting of conservation priorities is very important to have quantitative methods for quantifying the relative importance of species. We present an approach from the network perspective on ecology. Topological keystone species are those in critically important positions within the interaction network of an ecological community. Graph theory makes the quantification of the positional importance of nodes within networks possible. There are many ways to measure this and, in particular, we use some network indices recently introduced in social network analysis. These are suitable for the characterisation of both direct and indirect interactions. The key players of a hypothetical ecological community will be identified and the results of different methods will be compared. We emphasise that the need to find a quantitative, comparative approach to species importance is urgent and very important when outlining effective conservation efforts.