Toward reliable population estimates of wolves by combining spatial capture-recapture models and non-invasive DNA monitoring

Abstract

Decision-makers in wildlife policy require reliable population size estimates to justify interventions, to build acceptance and support in their decisions and, ultimately, to build trust in managing authorities. Traditional capture-recapture approaches present two main shortcomings, namely, the uncertainty in defining the effective sampling area, and the spatially-induced heterogeneity in encounter probabilities. These limitations are overcome using spatially explicit capture-recapture approaches (SCR). Using wolves as case study, and non-invasive DNA monitoring (faeces), we implemented a SCR with a Poisson observation model in a single survey to estimate wolf density and population size, and identify the locations of individual activity centres, in NW Iberia over 4,378 km 2 . During the breeding period, posterior mean wolf density was 2.55 wolves/100 km 2 (95%BCI = 1.87-3.51), and the posterior mean population size was 111.6 ± 18.8 wolves (95%BCI = 81.8-153.6). From simulation studies, addressing different scenarios of non-independence and spatial aggregation of individuals, we only found a slight underestimation in population size estimates, supporting the reliability of SCR for social species. The strategy used here (DNA monitoring combined with SCR) may be a cost-effective way to generate reliable population estimates for large carnivores at regional scales, especially for endangered species or populations under game management.Estimating the abundance of species is one of the most contentious issues in conservation and applied ecology 1,2 . Decision-makers in wildlife policy require reliable population size and density estimates to adopt and justify interventions. Reliability is essential to build acceptance and support in management decisions and, ultimately, trust in managing authorities. Otherwise, speculation and distrust can emerge after decisions are made, and may undermine entire management or conservation strategies 1,3 . Incorrect population estimates may lead to misinterpretations of the status of populations, the impact of interventions (e.g., hunting quotas or culling programs), or the degree to which conservation goals have been achieved.The management of large carnivores is controversial due to the multiple political, socio-economic and conservation interests involved. Information on population size or the impact of interventions is in constant demand, not only by managers, researchers and conservationists, but also by other interest groups. This is exemplified by recurrent debates around large carnivore numbers, particularly centred on endangered and charismatic species, such as in the case of tigers (Panthera tigris), lions (Panthera leo) or wolves (Canis lupus) [4][5][6][7][8] . Clear population targets are often established by managing authorities, and have become political issues, with reliable assessments of changes in large carnivore ranges and population size required to justify actions 9 .Wolves are a good example of a species whose estimates of population size and range are systemati...

Spatial density estimates of Eurasian lynx (Lynx lynx) in the French Jura and Vosges Mountains

“…multi-site dimension of our study allows exploring variability in the density estimates across landscapes. Our study is yet another example of the potential of combining SCR methods and noninvasive sampling techniques to estimate abundance and density for elusive and wide-ranging species, like large carnivores(Alexander et al, 2015;Broekhuis & Gopalaswamy, 2016;Goldberg et al, 2015;López-Bao et al, 2018;Pesenti & Zimmermann, 2013;Stetz et al, 2018).When examining densities across study areas in the French Jura mountains, we found spatial variation between the three counties, with Doubs area having the lowest densities, Ain the highest densities, and Jura intermediate densities. Our density estimates were of similar magnitude to other lynx populations in Europe: 1.47 and 1.38 lynx/100 km 2 in the Northwestern Swiss Alps(Pesenti & Zimmermann, 2013), 0.58 (Štiavnica mountains) and 0.81 individuals/100 km 2 (Velká Fatra National Park) in Slovakia(Kubala et al, 2017) and 0.9 individuals/100 km 2 in the Bavarian Forest National Park in Germany(Weingarth et al, 2012).…”

“…The multi‐site dimension of our study allows exploring variability in the density estimates across landscapes. Our study is yet another example of the potential of combining SCR methods and noninvasive sampling techniques to estimate abundance and density for elusive and wide‐ranging species, like large carnivores (Alexander et al, ; Broekhuis & Gopalaswamy, ; Goldberg et al, ; López‐Bao et al, ; Pesenti & Zimmermann, ; Stetz et al, ).…”

“…In addition, individual heterogeneity in detection due to spatial variation in the distance of home ranges to the sampling devices may lead to biased density estimates (Otis et al, 1978). Spatial capture-recapture (SCR) models deal with these issues by explicitly incorporating spatial locations of detections (Borchers, 2012;Borchers & Efford, 2008;Efford, 2004;Royle & Young, 2008), and they are increasingly used to estimate densities of large carnivores (Alexander, Gopalaswamy, Shi, & Face, 2015;Broekhuis & Gopalaswamy, 2016;Goldberg et al, 2015;López-Bao et al, 2018;Pesenti & Zimmermann, 2013;Stetz, Mitchell, & Kendall, 2018).…”

Integrating multiple genetic detection methods to estimate population density of social and territorial carnivores

“…North American gray wolves (Canis lupus), Mexican gray wolves (C. l. baileyi), and red wolves (C. rufus) are federally endangered in parts of the United States, whereas coyotes (C. latrans) have expanded range and present a number of management challenges in both wildland and urban environments, including hybridization with wolves (Kays et al 2009, Bohling and. Both coyotes and wolves tend to be highly territorial and strategically defecate to mark and communicate territory extents to conspecifics (Rothman and Mech 1979, Gese and Ruff 1997, Barja and List 2014; therefore, collecting scat samples along travel routes or at rendezvous sites has proven effective , Morin et al 2016, Piaggio et al 2016, L opez-Bao et al 2018. Although camera trapping is perhaps the most widely used method for noninvasively detecting wildlife (Foster and Harmsen 2012), the lack of individually unique natural markings (e.g., pelage spotting or striping) on wolves, coyotes, and other canids typically precludes individual identification from photographs.…”

“…In contrast, noninvasive genetic sampling that capitalizes on the ecological and behavioral characteristics of canids has become an efficient framework for detecting and individually identifying animals. Both coyotes and wolves tend to be highly territorial and strategically defecate to mark and communicate territory extents to conspecifics (Rothman and Mech 1979, Gese and Ruff 1997, Barja and List 2014; therefore, collecting scat samples along travel routes or at rendezvous sites has proven effective , Morin et al 2016, Piaggio et al 2016, L opez-Bao et al 2018). Furthermore, rubbing in odorous materials, such as carcasses of dead wildlife, is a natural behavioral response of canids (Ryon et al 1986, Martin and Farge 1988, Heffernan et al 2007, and collecting hair from lured ground-based rub pads has been used to detect both wolves and coyotes (Ausband et al 2011).…”