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

Corlatti, L., Nelli, L., Bertolini, M., Zibordi, F. and Pedrotti, L. (2017) A comparison of four different methods to estimate population size of Alpine marmot (Marmota marmota). Hystrix, 28(1), pp. 61-67. (doi:10.4404/hystrix-28.1-11698)

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Abstract

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 aimed to compare the performance of 4 different 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 (54,71)]; Poisson log-normal estimator: n=62 [95% CI (55,69)]}. Line distance sampling and double-observer methods were severely biased low {Line distance sampling: n=24 individuals [95% CI (19,31)]; Independent double-observer: n=24 [95% CI (22, 35)]; Dependent double-observer: 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 sampling scheme, the semifossorial behaviour of the target species is likely to lower the detection probabilities and violate the assumption of perfect detection on the transect.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Nelli, Dr Luca
Authors: Corlatti, L., Nelli, L., Bertolini, M., Zibordi, F., and Pedrotti, L.
College/School:College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
Journal Name:Hystrix
Publisher:Associazione Teriologica Italiana
ISSN:0394-1914
ISSN (Online):1825-5272
Published Online:22 February 2017
Copyright Holders:Copyright © 2017 The Authors
First Published:First published in Hystrix 28(1): 61-67
Publisher Policy:Reproduced under a Creative Commons License

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