Food web dynamics in the ocean. I. Best-estimates of flow networks using inverse methods

Abstract

We describe the application of inverse methods to the estimation of food web fluxes in undersampled ocean environments. The general objective is to deduce the flow networks that conserve mass, satisfy basic biological constraints, and are compatible with the observed structure of the food web. Given inevitable gaps in the observational data, a number of different networks will fit these requirements. In this paper, we estimate the simplest possible flow structure, that is, the network that minimizes (1) the sum total of the rate constants that relate flux to stock and (2) the differences among the constants. We present a general framework for the application of the inverse algorithm: (1) a linear compartmental model of the oceanic food web that initially includes all the possible inter-compartmen- tal fluxes, and (2) a set of constraints on the flow estimates that reflect contemporary knowledge of the limits and efficiencies of ecophysiological processes. The methodology is applied to detailed observa- tions of food web structure and dynamics in 2 areas off the English coast. The inverse solutions are discussed in terms of current concepts of the role of the microbial loop in the pelagic marine ecosystem. INTRODUCTION