Energetics and Stability in Belowground Food Webs

Abstract

The analysis of energy and material flow is considered to be fundamental to understanding the patterns and dynamics in ecosystems and the way ecosystems are organized (e.g., DeAngelis (1992) and Ulanowicz (1986)). The availability of energy to food webs has long been recognized to be an important factor influencing food web structure (e.g., Elton (1927), Lindeman (1942), McNaughton et al. (1989), and Wright (1990)), and has also been found to be related to food web stability (e.g., DeAngelis et al. (1989), DeAngelis (1992), and Moore et al. (1993)). Within food webs, energetics and population dynamics are deeply interrelated in that they both reflect the interactions among the populations (e.g., Hairston and Hairston (1993) and Moore et al. (1993)). These interactions influence population dynamics and represent transfer rates of energy and matter. It is by means of the population-dynamic descriptions of the interactions that we can analyze the stability of food web models (May, 1973). In real food webs, interactions are not random, but patterned, and these patterns influence the stability of the webs (e.g., May (1972), Pimm (1980), and Pimm et al. (1991)). In the same way, the nature and strength of the interactions are not random but patterned (e.g., Yodzis (1980, 1981)). An example of such a pattern is given by Moore and Hunt (1988) showing compartmentation along dominant flows of energy in the belowground food web from a short-grass prairie system. Compartmentation implies that the interactions among trophic groups within a compartment are frequent or strong relative to the interactions among compartments. This compartmentation along energy channels in real food webs corresponds with the Pidea of May (1972) that compartmented ecosystems are more likely to be stable than systems without compartmentation. How precisely the organization and transfer of energy within food webs are related to food web stability is yet unclear. Results of experiments establishing population-dynamic effects of a disturbance in interactions among trophic groups have not revealed a straightforward relationship with the energetics. Perturbations of interactions representing relatively small rates of material transfer sometimes lead to a large response, and perturbations of interactions representing a major pathway of material flow sometimes lead to a relatively small response (e.g., Paine (1980, 1992)). These experimental findings question whether a necessary link exists between the energetics in a food web and its stability.