The bioeconomics of tritrophic systems: applications to invasive species

Abstract

Adapted species in nature are assumed to have solved renewable resource management problems, and this is examined here using a physiologically based model of energy acquisition and allocation. Newly established invasive species are merely in an early phase of this process in their new environment. Analogies between the economies of humans and other species are used to develop an objective function for individual utility of energy allocation. The objective function includes the physiologically based population dynamics models of the consumer and resource species in a food chain as constraints. The model applies to all trophic levels in a food chain including human harvesting of renewable resources (see also Regev et al. (Regev, U., Gutierrez, A.P., Schreiber, S., Zilberman, D., 1998. Biological and Economic Foundation of Renewable Resource Exploitation. Ecological Economics. 26 (3), 227-242.)).

Specifically, the analysis:

• Attempts to combine ecological and economic theory;

• Points out the importance of time frame in the two economies (evolutionary vs. market time);

• Examines the effects of expected uncertainty due to environmental hazards in defining energy acquisition and allocation strategies in two invasive aphid species at the extremes of so called r- and K-strategies and the well adapted Central American cotton–cotton bollweevil system;

• Evaluates the effects of changes in behavioral and physiological parameters and environmental degradation on the abundance of resource and consumer species.

Introduction

Unlike humans, species in nature solve sustainable renewable resource management problems through the process of natural selection. We examine how this is done showing how the economies of plants and animals differ from that of humankind. Analogies between the two economies are used to develop an objective function “maximizing” individual utility of energy allocation in organisms. The use of economic analogies in ecology and vice-versa is not new (Ghiselin, 1995), nor has it been free of controversy (Rapport, 1991).

The comparative approach outlined here to examine interactions in a food chain is based on standard economic and ecological theory, but our approach differs from prior studies on optimal allocation of resources reviewed by Perrin and Sibley (1993), optimal foraging theory reviewed and criticized by Rapport (1991), and studies based on the theory of ecologically stable strategies (ESS). Unlike prior models of renewable resource management, the objective function in our model includes the physiologically based population dynamics models of the consumer and resource species as constraints. The model applies to all trophic levels in a food chain including human harvesting of renewable resource species. Regev et al. (1998) explored this latter topic and that paper should be considered dual to this one¹.

The underlying assumption of our model is that in adapted species, the observed phenotypes (including behavior and physiology) are the product of natural selection (Darwin, 1858), and hence, the strategies and the genes that code for them have survival value (sensu Dawkins, 1995). We note that selection has not been directed as the observed phenotypes carry the genetic burden of prior history of what worked (Gould, 1986). Furthermore, we cannot, except on rare occasions, see the survival value of a specific bit of DNA, rather we can only observe what phenotype organisms do, estimate the costs of the strategy they adopt and examine via models what would happen if they did something different. We make no argument that individual organisms choose optimal strategies despite the fact that we use optimization methods to understand the dynamics. Rather we assume at the start that the evolved strategy reflects an optimization strategy that is on average flexible enough to meet the expected variation in their biotic and abiotic environment (e.g., Gutierrez and Regev, 1983). Established invasive species may be viewed as being in transition toward adaptedness in their new environment, noting that most invasions fail.

All organisms, including plants and humans, are consumers (i.e., predators in a general sense), and all have the same problems of resource acquisition and allocation in priority order to egestion, conversion costs, respiration, reproduction and growth (including reserves). The economic analogies are respectively wastages, cost of doing business, costs of converting the raw material to a product, profit and firm growth (see Regev et al., 1998 for economic analogies). Energy fixed by plants during photo- (or chemosynthesis) passes up the trophic chain (web) to higher trophic levels as a more complete food. In our primal state, humans differed little from other animal species being both prey and predator. Over time there arose an innovative remnant (cf., Winters, 1971) that led to modern humans that enabled us to become the top predator in the food chain and to escape regulation of our numbers by natural enemies. As modern economies developed, harvests of renewable resources came to be valued by price, but despite this the acquisition and allocation of revenues have analogies to the acquisition and allocation of energy by organisms in nature (Fig. 1, cf., Gutierrez and Curry, 1989). Important analogies between ecology and economics were proposed by Winters (1971), Gutierrez and Regev (1983), Perrin and Sibley (1993), Regev et al. (1998), others and here, and hence the same economics model applies to both systems.