Partitioning ecosystems for sustainability.

Decline in the abundance of renewable natural resources (RNRs) coupled with increasing demands of an expanding human population will greatly intensify competition for Earth's natural resources during this century, yet curiously, analytical approaches to the management of productive ecosystems (ecological theory of wildlife harvesting, tragedy of the commons, green economics, and bioeconomics) give only peripheral attention to the driving influence of competition on resource exploitation. Here, I apply resource competition theory (RCT) to the exploitation of RNRs and derive four general policies in support of their sustainable and equitable use: (1) regulate resource extraction technology to avoid damage to the resource base; (2) increase efficiency of resource use and reduce waste at every step in the resource supply chain and distribution network; (3) partition ecosystems with the harvesting niche as the basic organizing principle for sustainable management of natural resources by multiple users; and (4) increase negative feedback between consumer and resource to bring about long-term sustainable use. A simple policy framework demonstrates how RCT integrates with other elements of sustainability science to better manage productive ecosystems. Several problem areas of RNR management are discussed in the light of RCT, including tragedy of the commons, overharvesting, resource collapse, bycatch, single species quotas, and simplification of ecosystems.

Resource-ratio theory applied to large herbivores.

The theoretical description of exploitation competition, known as resource competition theory (RCT) or resource-ratio theory, has been tested in terrestrial plant communities and microorganisms in laboratory cultures. Applications in animal ecology have been rare, although the theory itself is generic. A major difficulty is that the description of resources in RCT is fundamentally different from that used in classical studies of animal competition. In presenting the first fully specified RCT models for terrestrial animals, we distinguish between positive attributes (mineral elements) and negative attributes (plant defenses) as indicators of quality in animal resources. Using the latter we apply RCT to ungulate communities that exploit just two resources: the cell wall and cell contents of plant material. We show how coexistence in the same habitats depends on the strategy of resource exploitation. Ungulate species that differ in body size adopt a "demand-minimizing" strategy that permits them to coexist on ratios of the two resources by acquiring less of the resource that most limits their competitor. Ungulates that differ in mouth width adopt an "extraction-maximizing" strategy that leads to competitive exclusion because they acquire more of the resource that most limits their competitor. We conclude that differential resource utilization permits grazing herbivores of different body size to coexist on the same grassland habitats, but that the full diversity of grazing communities depends on spatial heterogeneity in plant defenses at the landscape level.

An inverse relationship between the cost of static posture and the cost of cycling?

To test the hypothesis that both species and individuals with low metabolic costs in locomotion have high energetic costs in maintaining static posture (and vice versa), energy expenditure was measured in men engaged in different activities. Subjects were asked to exercise on a cycle ergometer at different speeds at constant work rates and to maintain a set isometric tension when sitting using different angles of the knee. Individuals with a low energy cost of sitting (minus BMR) had a high energy cost of cycling at 50 rev/min at an external work rate of 25 W (minus energy cost in a sitting position on the cycle). However, there was no significant correlation between the energy cost during a dynamic cycling task and the energy cost during maintenance of a standardized static posture. These findings suggest that mechanisms involved in the conservation of energy expended during cycling may be different from those involved during maintenance of standardized static postures. Curves relating energy expenditure to speed (for a constant work rate) were remarkably flat in the range 20-70 rev/min, indicating a difference in the way energy is conserved in cycling and within gaits. © 1992 Wiley-Liss, Inc.