Effects of direct human disturbance on the endemic Iberian frog Rana iberica at individual and population levels

There is widespread concern about the global decline of amphibians, but little is known about whether and how direct human disturbance might affect populations. The goal of this study was to assess the effects of recreational activities on Iberian frogs Rana iberica, an endemic and vulnerable species of the Iberian Peninsula, through observation and manipulative approaches. At the population level, we found that frog abundance decreased with the proximity to recreational areas. At the individual level, the behavioral responses of frogs to repeated disturbance events increased the time to resume pre-disturbance activities, but did not affect significantly flight initiation distances. We simulated different levels of human visitation to the stream banks, and found 80% and 100% decrease in stream bank use with a fivefold and a 12-fold increase in direct disturbance rate, respectively. Recreational activities are negatively affecting Iberian frogs through a loss in the spatial and temporal availability of resources. To reduce the level of local disturbance to this species, we recommend setting up buffer areas >2.5 m from the streams or reducing visitor rates to fewer than 5 visits per hour (either groups or individuals). The role of direct human disturbance should be considered further as a potential factor affecting local amphibian declines.