Geographical assignment of polar bears using multi-element isoscapes

Abstract

Wide-ranging apex predators are among the most challenging of all fauna to conserve and manage. This is especially true of the polar bear ( Ursus maritimus ), an iconic predator that is hunted in Canada and threatened by global climate change. We used combinations of stable isotopes ( 13 C, 15 N, 2 H, 18 O) in polar bear hair from > 1000 individuals, sampled from across much of the Canadian Arctic and sub-Arctic, to test the ability of stable isotopic profiles to ‘assign’ bears to (1) predefined managed subpopulations, (2) subpopulations defined by similarities in stable isotope values using quadratic discriminant analysis, and (3) spatially explicit, isotopically distinct clusters derived from interpolated (i.e. ‘kriged’) isotopic landscapes, or ‘isoscapes’, using the partitioning around medoids algorithm. A four-isotope solution provided the highest overall assignment accuracies (~80%) to pre-existing management subpopulations with accuracy rates ranging from ~30–99% (median = 64%). Assignment accuracies of bears to hierarchically clustered ecological groups based on isotopes ranged from ~64–99%. Multivariate assignment to isotopic clusters resulted in highest assignment accuracies of 68% (33–77%), 84% (47–96%) and 74% (53–85%) using two, three and four stable isotope groups, respectively. The resulting spatial structure inherent in the multiple stable isotopic compositions of polar bear tissues is a powerful forensic tool that will, in this case, contribute to the conservation and management of this species. Currently, it is unclear what is driving these robust isotopic patterns and future research is needed to evaluate the processes behind the pattern. Nonetheless, our isotopic approach can be further applied to other apex mammalian predators under threat, such as the large felids, providing that isotopic structure occurs throughout their range.

Zinc isotopes from archaeological bones provide reliable trophic level information for marine mammals

“…1a ). The δ 15 N and δ 13 C variability between the archaeological sites is in good agreement in both spacing and amplitude with modern geographical variations observed from zooplankton 28 , 45 , 46 and higher consumer soft tissue 6 , 49 including P. hispida 37 , 53 , 54 , 74 – 76 and U. maritimus 33 . While dietary differences between populations may have contributed to the geographic spacing of δ 15 N and δ 13 C values, integration of regional baseline isotopic patterns is likely the main factor controlling the observed inter-site isotopic variability in P. hispida and U. maritimus collagen (Supplementary Discussion 3.3 ).…”

“…Focusing on these species allows us to investigate δ 66 Zn trophic level isotope discrimination factors between predator and prey geographically. Both species have a circumpolar Arctic distribution and are abundant throughout the Arctic today 32 , 33 . Particularly, P. hispida remains are frequently found in archaeological assemblages with a large temporal and spatial range 30 , 34 , 35 .…”

Advantages of zinc isotopes as a new dietary proxy in marine ecology

“…1a). The  15 N and  13 C variability between the archaeological sites is in good agreement in both spacing and amplitude with modern geographical variations observed from zooplankton 26,27,28 and higher consumer soft tissue 6,27,28,31 including P. hispida 51,52,53,54,55,56 and U. maritimus 46 . While dietary differences between populations may have contributed to the geographic spacing of  15 N and  13 C values, an integration of regional baseline isotopic patterns is the main factor controlling the observed inter-site isotopic variability in P. hispida and U. maritimus collagen (Supplementary Discussion).…”

“…Focusing on these species allows us to investigate  66 Zn trophic level isotopic discrimination factors between predator and prey geographically. Both species have a circumpolar Arctic distribution and are abundant throughout the Arctic today 45,46 . Particularly, P. hispida remains are frequently found in archaeological assemblages with a large temporal and spatial range 43,47,48 .…”

On the identity of the tamarin AMNH 98303 (“<i>Saguinus fuscicollis tripartitus</i>”; Primates: Haplorrhini: Simiiformes: Platyrrhini: Callitrichidae)

“…For comparison, mtDNA sequences are available for a large number of Leontocebus taxa (Matauschek et al, 2011;Buckner et al, 2015;Sampaio et al, 2015). Stable isotope analyses could also help to explore its geographic origin (Koehler et al, 2019;Dominy et al, 2020). Also, other museums could revise their tamarin collections to see whether they include specimens that phenotypically match AMNH 98303.…”