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Title: Factors affecting southern water vole (Arvicola sapidus) detection and occupancy probabilities in Mediterranean farmland
Authors: Peralta, Dinora
Leitão, Inês
Ferreira, António
Mira, António
Beja, Pedro
Pita, Ricardo
Keywords: Agricultural landscapes
Imperfect detection
Occupancy models
Presence signs
Issue Date: 2016
Publisher: Mammalian Biology
Citation: Peralta, D.; Leitao, I.; Ferreira, A.; Mira, A.; Beja, P.; Pita, R. 2016. Factors affecting southern water vole (Arvicola sapidus) detection and occupancy probabilities in Mediterranean farmland. Mammalian Biology, 81(2): 123-129.
Abstract: Failure to detect a species at sites where it is present (i.e. imperfect detection) is known to occur frequently, but this is often disregarded in monitoring programs and metapopulation studies. Here we modelled for the first time the probability of patch occupancy by a threatened small mammal, the southern water vole (Arvicola sapidus, while accounting for the probability of detection given occupancy. Based on replicated presence sign surveys conducted in autumn (November–December 2013) and winter (February–March 2014) in a farmland landscape, we used occupancy detection modelling to test the effects of vegetation, sampling effort, observer experience, and rainfall on detection probability. We then assessed whether occupancy was related to patch size, isolation, vegetation, or presence of water, after correcting for imperfect detection. The mean detection probabilities of water vole signs in autumn (0.71) and winter (0.81) indicated that false absences may be generated in about 20–30% of occupied patches surveyed by a single observer on a single occasion. There was no statistical support for the effects of covariates on detectability. After controlling for imperfect detection, the mean probabilities of occupancy in autumn (0.31) and winter (0.29) were positively related to patch size and presence of water, and negatively so, albeit weakly, to patch isolation. Overall, our study underlined the importance of accounting for imperfect detection in sign surveys of small mammals such as water voles, pointing out the need to use occupancy detection modelling together with replicate surveys for accurately estimating occupancy and the factors affecting it.
Type: article
Appears in Collections:MED - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica
BIO - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica

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