Riparian disturbance restricts in-stream movement of salamanders

Long-term population persistence or population rescue require dispersal from other source populations. Barriers to movement can effectively fragment and isolate populations, reducing persistence and recolonisation. For stream organisms that depend heavily on movement within dendritic networks, research is needed to identify and estimate the effects of such barriers on connectivity. We used capture-mark-recapture of displaced larval and adult salamanders to estimate return rates across gaps (length 13-85 m) in the riparian canopy and thus to assess the fragmentation of salamander populations within otherwise fully forested catchments. Relative to salamanders in fully forested reaches, displaced salamanders were 86% less likely to return to their capture location when required to cross gaps in the canopy as short as 13 m, and the likelihood of return declined with increasing gap length. The effects of gaps on return rates were consistent among life stages and for up- and downstream movement. Our study suggests that riparian disturbance can reduce permeability to salamanders, even in the absence of additional land-use change. Because anthropogenic features, such as roads and powerlines, frequently cross small streams, the accumulation of apparently small land-cover changes has the potential to reduce continuous populations to small fragments with limited connectivity.