Time-to-detection Occupancy Modeling: An Efficient Method for Analyzing the Occurrence of Amphibians and Reptiles
Occupancy models provide a reliable measure of species distributions while accounting for imperfect detectability. The cost of accounting for false absences is that occupancy surveys typically require repeated visits to a site or multiple-observer techniques. More efficient methods of estimating detection probabilities would allow more sites to be surveyed for the same effort, resulting in more information about the ecological processes leading to occupancy. Time-to-detection surveys allow the estimation of detection probability based on a single site visit by one observer, and therefore might be an efficient technique for herpetological occupancy studies. We evaluated the use of time-to-detection surveys to estimate the occupancy of pond-breeding amphibians at Point Reyes National Seashore, California, USA, including variables that affected detection rates and the probability of occurrence. We found that detection times were short enough and occupancy high enough to reliably estimate the probability of occurrence of three pond-breeding amphibians at Point Reyes National Seashore, and that survey and site conditions had species-specific effects on detection rates. In particular, relative abundance was negatively related to the time to initial detection of all species, and pond area was positively related to time to initial detection for Sierran Treefrogs (Hyliola sierra) and Rough-skinned Newts (Taricha granulosa). Rough-skinned newt time to initial detection also was affected by date, with lowest initial detection time in early summer. California Red-legged Frog (Rana draytonii) time to detection was lowest in ponds with a mean depth of 0.6 m, and higher in shallower and deeper ponds. Probability of occurrence of Sierran Treefrogs and Rough-skinned Newts was negatively related to the presence of fish and pond area. Rarely detected species required constraints on priors to fit time-to-detection models. Time-to-detection surveys can provide an efficient method of estimating detection probabilities and accounting for false absences in occupancy studies of reptiles and amphibians.
|Outlet/Publisher:||Journal of Herpetology 52:416-425|