A comparison of four methods to estimate population size of Alpine marmot (Marmota marmota)

作者：Corlatti Luca; Nelli Luca; Bertolini Matteo; Zibordi Filippo; Pedrotti Luca^*

来源：Hystrix - The Italian Journal of Mammalogy, 2017, 28(1).

DOI：10.4404/hystrix-28.1-11698

• abundance
• capture-mark-recapture
• distance sampling
• double-observer
• mark-resight
• surveys

Obtaining reliable information on animal abundance in mountainous landscapes is challenging. Highly heterogeneous habitats tend to reduce detection probabilities, and the three-dimensional, rugged nature of the terrain poses severe limits to the fulfilment of a number of assumptions underlying several statistical methods. In this study, we compared the performance of 4 methods to estimate population size of Alpine marmot (Marmota marmota), a highly social semifossorial rodent widely distributed on the European Alps. Between May and August 2015, in a study area within the Stelvio National Park (Italy), we conducted 8 sessions of capture-mark-recapture, 6 sessions of mark-resight from vantage points, 8 sessions of line distance sampling along 4 transects, and 2 sessions using double-observer methods from vantage points. The minimum number of animals alive, obtained during the mark-resight surveys, was n= 54 individuals. Capture-mark-recapture models estimated a population size of n= 56 individuals (95% CI= 45-87); similar, but more precise estimates were obtained with the mark-resight approach (Bowden's estimator: n= 62, 95% CI= 5471; Poisson log-normal estimator: n= 62, 95% CI= 55-69). Line transect distance sampling and double-observer methods were severely biased low (line transect distance sampling: n= 24 individuals, 95% CI= 19-31; independent double-observer: n= 24, 95% CI= 22-35; dependent doubleobserver: n= 15, 95% CI= 15-20). Our results suggest that the probabilistic approach based on marked individuals yielded fairly robust estimates of population size. The underestimates obtained using distance sampling and double-observer methods were likely due to the violation of some underlying assumptions. While the topography of the mountainous landscape makes it difficult to randomize the distribution of line transects, the burrowing behaviour of the species is likely to violate the assumption of perfect detection on the transect; in addition, the semifossorial habits of marmots lower their detection probabilities, thus hampering the performance of these methods.

• 出版日期2017