Structural food web regimes

Ecological network analysis allows for an investigation of the structural and functional inter-connectedness in ecosystems. Typically, these interactions are seen to comprise a food web of "who eats whom", but more generally applies to the transfer of energy-matter within the biotic and abiotic ecosphere. This web of transactions can be depicted as a digraph or an adjacency matrix in which the presence of direct transactions are represented as a I and no transactions as 0. Each transaction between system components leads to an overall network structural pattern. These structures cluster into different categories or regimes based on their cyclic nature. This paper demonstrates threshold effects of the placement or removal of links, such that certain changes essentially keep the structure in the same regime whereas others shift it to another regime in a non-linear manner. (C) 2007 Elsevier B.V. All rights reserved.