Monitoring Strategy for Eight Amphibian Species in French Guiana, South America

Abstract

Although dramatic amphibian declines have been documented worldwide, only few of such events have been quantitatively documented for the tropical forests of South America. This is due partly to the fact that tropical amphibians are patchily distributed and difficult to detect. We tested three methods often used to monitor population trends in amphibian species in a remote lowland tropical forest of French Guiana. These methods are capture-mark-recapture (CMR), estimation of the number of calling males with repeated counts data and distance sampling, and rates of occupancy inferred by presence/absence data. We monitored eight diurnal, terrestrial amphibian species including five Dendrobatidae and three Bufonidae. We found that CMR, the most precise way of estimating population size, can be used only with two species in high density patches where the recapture rate is high enough. Only for one of the species (Dendrobates tinctorius), a low coefficient of variation (CV = 0.19) can be achieved with 15 to 20 capture events. For dendrobatid species with day-calling males, audio surveys yield a better probability of detection with only 8 audio surveys needed; quantitative estimates can be achieved by computing the number of calling males inferred from audio counts or distance sampling analysis. We therefore suggest that an efficient monitoring protocol for Neotropical amphibian species should include a combination of sighting and audio techniques, and we discuss the need of implementing a large-scale monitoring in order to provide a baseline for comparison with future changes.

The power of monitoring: optimizing survey designs to detect occupancy changes in a rare amphibian population

“…itambe may be an unusual model for a rare and threatened species. Estimates of amphibian detection are frequently low 20 , 22 , 43 , 55 and this is particularly challenging for population monitoring. Although strong inferences on population trends are mostly needed for rare and cryptic species, these are the very taxa that display low detectability or occupancy rates (or both).…”

“…Although strong inferences on population trends are mostly needed for rare and cryptic species, these are the very taxa that display low detectability or occupancy rates (or both). Amphibian detectability can be improved by conducting surveys with multiple observers or repeating sampling occasions in a single night 13 , increasing the number of traps and/or reducing the sampling area 43 , combining different sampling methods 20 , 22 , 56 or surveying under ideal weather conditions 19 . However, it may be more costly to obtain precise estimates for rare and cryptic species because of the increased sampling effort needed.…”

“…Very often sampling designs are unlikely to provide sufficient power to detect small changes in estimated parameters 9 , 27 , 28 especially for less detectable species 58 . Statistical power to detect small changes can be increased by changing the sampling design, usually (if not always) by increasing sampling effort 5 , 9 , 22 , 25 , 27 – 29 , 59 . In our case, increasing the number of sampling occasions had only a small effect on statistical power.…”

“…Occupancy models estimate site occupancy and detection probabilities in an unbiased way 13 , 14 and occupancy may also be used as a proxy for abundance 6 . Although sampling designs for occupancy models have been explored theoretically 15 – 18 , few studies have used empirical data to investigate the survey effort required for the reliable inference of absence 19 – 21 or to explore the precision and accuracy of occupancy estimates 22 – 24 . In the context of occupancy monitoring, studies have also considered statistical power using empirical data 8 , 24 – 29 .…”

Widespread Occurrence of Bd in French Guiana, South America

“…For future Bd surveillance, it is also of importance to determine sentinel species to focus efforts on the most susceptible species and to detect the presence of Bd unambiguously. D endrobates tinctorius , Allobates femoralis and Anomaloglossus baeobatrachus displayed the highest Bd prevalence in this study and are locally abundant [ 49 ]. Moreover, we observed an increase of Bd prevalence in two species ( D .…”