Long-term persistence of amphibian populations in a restored wetland complex

Abstract

Although breeding habitats for amphibians are frequently created in restored wetlands, populations at restored sites often have no connectivity to neighboring populations and are vulnerable to site-wide extinctions. We conducted a 13-year study to examine the persistence of amphibian populations at a geographically isolated restoration site in western North Carolina. We created a complex of breeding sites that were intended to buffer populations from environmental stressors and to enhance population persistence. Our primary efforts involved monitoring the use of 10 constructed and 10 reference ponds on site. We estimated annual juvenile production of the wood frog (Lithobates sylvaticus) and spotted salamander (Ambystoma maculatum) based on the number of larvae in ponds at the initiation of metamorphosis. We documented changes in adult breeding population size based on annual censuses of egg masses. Most constructed and reference ponds failed to produce juveniles annually between 1998 and 2006 as a result of stressors that included a drought, outbreaks of a lethal pathogen (Ranavirus), and the widespread occupancy of constructed ponds by fish. Despite numerous reproductive failures, a few ponds produced juveniles annually at rates that allowed wood frog and spotted salamander populations to persist at high levels. Both species exhibited strong resistance to environmental stressors, and none of six other pond-breeding amphibians that were monitored suffered site-wide extinctions from 1996 to 2006. Our results provide evidence that complex wetland designs may enhance the resistance and long-term persistence of populations that have little or no connectivity to neighboring populations. © 2007 Elsevier Ltd. All rights reserved.