Conserving connectivity: Human influence on subsidy transfer and relevant restoration efforts

Abstract

Conservation efforts tend to focus on the direct impacts humans have on their surrounding environment; however there are also many ways in which people indirectly affect ecosystems. Recent research on ecological subsidies-the transfer of energy and nutrients from one ecosystem to another-has highlighted the importance of nutrient exchange for maintaining productivity and diversity at a landscape scale, while also pointing toward the fragility of ecotones and vulnerability of subsidies to human activities. We review the recent literature on landscape connectivity and ecosystem subsidies from aquatic systems to terrestrial systems. Based on this review, we propose a conceptual model of how human activities may alter or eliminate the flow of energy and nutrients between ecosystems by influencing the delivery of subsidies along the pathway of transfer. To demonstrate the utility of this conceptual model, we discuss it in the context of case studies of subsidies derived from salmon, marine mammals, sea turtles, sea birds, and shoreline debris. Subsidy restoration may require a different set of actions from simply reversing the pathway of degradation. We suggest that effective restoration and conservation efforts will require a multifaceted approach, targeting many steps along the subsidy transfer pathway, to address these issues.

Keywords: Conservation; Ecological subsidies; Ecotone; Landscape connectivity.

Fig. 1

Conceptual model highlighting the three different ways by which human activities may influence the quantity or quality of an ecological subsidy as it moves from its system of origin (‘donor’ system) to its destination (‘recipient’ system). (1) When human activity within the donor system leads to a decline in the subsidy’s availability, (2) when human activity along an ecosystem boundary blocks the transfer of the subsidy, and (3) when human activity within the recipient system leads to a decline in the subsidy’s facilitator. For each category, we have provided examples of human activities, whether those activities are top-down or bottom-up mediated, and the subsequent effects those activities may have on the subsidy in question