Conservation in a changing world: Do we need a disequibrium theory of ecology?

Background/Question/Methods

The rapid pace of environmental change in the next century is expected to cause widespread and pervasive changes in the structure and function of ecological communities. The conceptual framework of conservation biology is being widely reevaluated, as the idea of conserving or restoring historical conditions appears increasingly elusive. The paleoecological record offers pervasive evidence of large-scale species movement and changing community composition in response to changing climates. In communities dominated by long-lived or slow-dispersed organisms, trees in particular, these changes often transpire over hundreds to thousands of years. By implication, conservation biologists may be faced with transient dynamics, or disequilibrium communities, for the foreseeable future. The central question of this talk is whether a new ‘disequilibrium’ theory of ecology is needed, or whether the existing conceptual tools will be adequate to address the transient dynamics of ecological change and guide the practical strategies and tactics of conservation biology.

Results/Conclusions

We identify four, interrelated theoretical frameworks that address these challenges: 1) critical transitions and alternative stable (or transient) regimes; 2) limits to species distributions, and dynamics of leading and trailing edges; 3) disturbance and succession, with a need to incorporate underlying changes in environmental conditions; and 4) priority effects and demographic inertia, i.e. the contingency of historical effects in community assembly. Unfortunately, while these frameworks all suggest that disequilibrial responses are likely to be common, it is difficult to make critical predictions such as the duration of disequilibrium, community composition during transient transitions and the mechanisms which can prolong or truncate disequilibrium dynamics.  The situation is further complicated in conservation planning because the endpoint equilibrial conditions are a “moving target” as climate and land use continue to change in the future. In this framework, conservation strategies can be evaluated in terms of their impacts on the rates of critical processes (e.g., enhancing dispersal to reduce disequilibrium), their ability to minimize the impacts of disequilibrium conditions (e.g., reducing undesirable invasives until native plants can establish), and their effects on the sign and magnitude of feedback processes that can enhance resilience or facilitate transitions to desired conditions.