The Problem of Nontrophic Processes in Trophic Ecology: Toward a Network Unfolding Solution

Abstract Energy and matter enter, exit, and circulate in ecosystems by a variety of processes; one of these is feeding. These processes collectively give rise to energy-matter flow-storage networks, of which food webs, defined by ingestion and assimilation transformations, are the most studied as discrete subwebs. How to deal with mixed trophic and nontrophic processes has been problematic in trophic ecology since Lindeman (1942) first applied Hutchinson's (1941) concept of trophic chains to lacustrine food cycles. In this paper we develop a method to separate feeding from non-feeding flows in the conversion of arbitrary networks to transfer macrochains by network unfolding (Higashi et al. , 1989, 1991, 1992). This enables analysis of the quantitative role of different flow processes in the transfer macrochain. We apply the method to a 24-compartment Okefenokee Swamp marsh ecosystem model which is 21% connected and has a Finn cycling index of 0·445 (Finn, 1976, 1978). Trophic versus nontrophic flows oscillate in their relative contributions to successive levels of the unfolded macrochain for this model, but by the 24th transfer level the oscillations damp and converge toward a point where the proportion of nontrophic flow equals the cycling index. Thus, the majority of trophic flows are essentially acyclic in this cyclic model, despite the presence of food cycling by carnivorous plants and instances of mutual predation. This corresponds to the typical acyclic structure of literature food webs. Work will continue toward being able to suppress incrementation of transfer levels when the transfer processes are nontrophic. This will enable a strict definition of trophic levels within networks of mixed trophic and nontrophic structure.