Genetic analysis reveals demographic fragmentation of grizzly bears yielding vulnerably small populations

Abstract

Ecosystem conservation requires the presence of native carnivores, yet in North America, the distributions of many larger carnivores have contracted. Large carnivores live at low densities and require large areas to thrive at the population level. Therefore, if human-dominated landscapes fragment remaining carnivore populations, small and demographically vulnerable populations may result. Grizzly bear range contraction in the conterminous USA has left four fragmented populations, three of which remain along the Canada-USA border. A tenet of grizzly bear conservation is that the viability of these populations requires demographic linkage (i.e. inter-population movement of both sexes) to Canadian bears. Using individualbased genetic analysis, our results suggest this demographic connection has been severed across their entire range in southern Canada by a highway and associated settlements, limiting female and reducing male movement. Two resulting populations are vulnerably small (%100 animals) and one of these is completely isolated. Our results suggest that these trans-border bear populations may be more threatened than previously thought and that conservation efforts must expand to include international connectivity management. They also demonstrate the ability of genetic analysis to detect gender-specific demographic population fragmentation in recently disturbed systems, a traditionally intractable yet increasingly important ecological measurement worldwide.

Genetic and genomic monitoring with minimally invasive sampling methods

“…MIS using microsatellites has also been valuable for assessing the effectiveness of corridors (Dixon et al, 2006) and evaluating potential barriers (Epps et al, 2005;Kendall et al, 2009;Proctor et al, 2005). More recently, SNPs have been utilized to estimate pedigree-based dispersal models in brown bears (Norman et al, 2015) and to infer individual provenance (i.e., identify potential migrants) based on the distribution of pairwise relatedness (DeWoody et al, 2017).…”

“…In the last 25 years, researchers have demonstrated a variety of important applications of MIS including detecting rare species (Palomares et al, 2002;Valière et al, 2003), estimating population size and other demographic parameters (Carroll et al, 2013;Kendall et al, 2009;M. H. Kohn et al, 1999;Rudnick et al, 2005;Woodruff et al, 2016;Woods et al, 1999), evaluating genetic diversity and gene flow (Epps et al, 2005;Gerloff et al, 1999;Lucchini et al, 2002;Palsbøll et al, 1997), detecting movement and migration (Dixon et al, 2006;Proctor et al, 2005), evaluating social structure (Constable et al, 2001;Ford et al, 2011;Morin et al, 1994), detecting hybridization (Adams et al, 2003;Bohling et al, 2016;Steyer et al, 2016), monitoring disease epizootics (M. H. Kohn & Wayne, 1997;Schunck et al, 1995), identifying diet items (De Barba et al, 2016;Höss, 1992;Taberlet & Fumagalli, 1996), and wildlife forensic applications (Banks et al, 2003;Ernest et al, 2002;Lukoshek et al, 2009;Wasser et al, 2004).…”

Fragmentation, dispersal and metapopulation function in remnant populations of endangered mountain caribou

“…Near the southern edge of their distribution, they too are found in small, isolated subpopulations (Proctor, McLellan & Strobeck, 2002). Although some subpopulations are gradually expanding their range (Schwartz et al, 2006), limited dispersal, particularly by females, (McLellan & Hovey, 2001;Proctor et al, 2002Proctor et al, , 2005, has prevented them from recolonizing any of 30 patches that contained bears a century ago (Merriam, 1922), despite complete protection in the US since 1975. Wolves, on the other hand, disperse widely (Fritts, 1983;Lehman et al 1992;Forbes & Boyd, 1997), possibly an adaptation to avoid inbreeding as unlike bears or caribou, wolves are territorial.…”

“…Genetic analysis was not used because the overall population has been declining (Wittmer et al, 2005a) and half of the subpopulations have 30 or fewer animals. With necessarily small sample sizes per subpopulation and the declining population paradigm suggesting recent fragmentation, there was insufficient genetic structuring to identify putative migrants as has been carried out with other species with increasing movements (Proctor et al, 2005;Dixon et al, 2006;Paetkau et al, 2009). Furthermore, small and rapidly declining populations are not at 'migration-drift' equilibrium making it inappropriate to estimate migrants using classic population genetics (Whitlock & McCauley, 1999).…”

Genetic evidence for spatial structuring in a continuous African elephant (Loxodonta africana) population

“…in amphibians (Dixo et al 2009), birds (Segelbacher et al 2003), mammals (Proctor et al 2005) and reptiles (Gibbon et al 2000)). The African savannah elephant (L. africana) typifies this scenario in that the over-exploitation (e.g.…”