When no color pattern is available: Application of double observer methods to estimate population size of the Alpine salamander

ABSTRACT

Monitoring wild populations is an essential tool to assess the conservation status and the ecological requirements of a species. Capture–mark–recapture (CMR), based on individual recognition, is the most commonly used and most effective technique. However, in cases of species with no individual color pattern, tracing the encounter history of individuals without invasive marking methods is impossible. In this study we aimed to (1) estimate population abundance and density using a less effort-intensive and nonstressful technique, (2) test a long-term monitoring protocol, and (3) assess the fine-scale ecological requirements of a black-colored amphibian, Salamandra atra, in the Italian Alps. For three populations we applied an N-mixture model on data collected using a dependent double-observer approach. To understand ecological requirements, we assessed the relative importance of a set of environmental and topographical variables. The double-observer approach was a cost-effective technique that provided reliable demographic estimates of population density. Our results suggest that the most important fine-scale ecological variables positively associated with salamander abundance were canopy cover and terrain ruggedness, which are strictly related to shelter availability and soil moisture.

KEYWORDS:

• Abundance estimation
• Alps
• amphibians
• double observer
• salamanders

Acknowledgments

The Paneveggio–Pale di San Martino Natural Park provided logistic facilities close to the sampling site. In particular, we are grateful to the Technical Coordinator Piergiovanni Partel, the Director Vittorio Ducoli, and the park guard Gilberto Volcan. Thanks to Rachele Gobbi for the contributions to field sampling.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study is a part of the Natura 2000 Network Habitat Directive monitoring and was partially supported by Servizio Aree Protette e Sviluppo Sostenibile PAT (Piano di monitoraggio fauna vertebrata Direttiva Habitat; Progetto LIFE11/ NAT/IT/000187 “TEN”–Trentino Ecological Network) and by the Paneveggio–Pale di San Martino Natural Park (Fondi Piano di Sviluppo Rurale PAT).