HYDROLOGIC CONNECTIVITY AND THE MANAGEMENT OF BIOLOGICAL RESERVES: A GLOBAL PERSPECTIVE

Increasingly, biological reserves throughout the world are threatened by cumulative alterations in hydrologic connectivity within the greater landscape. Hydrologic connectivity is used here in an ecological sense to refer to water‐mediated transfer of matter, energy, and/or organisms within or between elements of the hydrologic cycle. Obvious human influences that alter this property include dams, associated flow regulation, groundwater extraction, and water diversion, all of which can result in a cascade of events in both aquatic and terrestrial ecosystems. Even disturbances well outside the boundaries of reserves can have profound effects on the biological integrity of these “protected” areas. Factors such as nutrient and toxic pollution and the spread of nonnative species are perpetuated by hydrologic connectivity, and their effects can be exacerbated by changes in this property. Hydrological alterations are now affecting reserves through increasingly broad feedback loops, ranging from overdrawn aquifers to atmospheric deposition and global climate change. Such alterations are often beyond the direct control of managers because they lie outside reserve boundaries, and data on hydrologic connection between reserves and surrounding landscapes are scant. The subject of water has also been typically excluded from the literature pertaining to both theoretical and practical aspects of reserve size, isolation, and design. This results, in part, from early management strategies developed when the landscape matrix outside of reserves was not excessively fragmented, and when awareness of hydrologic connectivity was in its infancy. The location of a given reserve within a watershed, relative to regional aquifers and wind and precipitation patterns, can play a key role in its response to human disturbance transmitted through the hydrologic cycle. To illustrate this point, I discuss reserves of varying sizes from diverse regions throughout the world. Reserves located in middle and lower watersheds often suffer direct hydrologic alterations that cause severe habitat modification and exacerbate the effects of pollution. In contrast, reserves in upper watersheds may have intact physical habitat and contain important source populations of some native biota, yet hydrologic disturbances in lower watersheds may cause extirpation of migratory species, cascading trophic effects, and genetic isolation. Worldwide, <7% of land area is either strictly or partially protected, and many reserves are in danger of becoming population “sinks” for wildlife if we do not develop a more predictive understanding of how they are affected by hydrologic alterations that originate outside of their boundaries. For reprints of this Invited Feature, see footnote 1, p. 945.