Research: Intrapopulation diversity in isotopic niche over landscapes: Spatial patterns inform conservation of bear–salmon systems

New dietary study reveals salmon hotspots for grizzly and black bears across 700,000 square kilometres

Overview: A new study by scientists at Raincoast and the University of Victoria shows hotspots of salmon consumptions by bears across a huge expanse of western North America.  The study showed clear patterns on a landscape scale. Salmon-bearing waterways punctuate into British Columbia over hundreds of kilometres. The authors found that grizzly bears – especially males – access this resource over 1,000 km into interior habitats. These findings were published in the peer-reviewed open-access journal, Ecosphere.

Abstract:

Intrapopulation variability in resource acquisition (i.e., niche variation) influences population dynamics, with important implications for conservation planning. Spatial analyses of niche variation within and among populations can provide relevant information about ecological associations and their subsequent management. We used stable isotope analysis and kernel-weighted regression to examine spatial patterns in a keystone consumer–resource interaction: salmon (Oncorhynchus spp.) consumption by grizzly and black bears (Ursus arctos horribilis, n = 886; and Ursus americanus, n = 557) from 1995 to 2014 in British Columbia (BC), Canada. In a region on the central coast of BC (22,000 km2), grizzly bears consumed far more salmon than black bears (median proportion of salmon in assimilated diet of 0.62 and 0.06, respectively). Males of both species consumed more salmon than females (median proportions of 0.63 and 0.57 for grizzly bears and 0.06 and 0.03 for black bears, respectively). Black bears showed considerably more spatial variation in salmon consumption than grizzlies. Protected areas on the coast captured no more habitat for bears with high-salmon diets (i.e., proportions >0.5 of total diet) than did unprotected areas. In a continental region (~692,000 km2), which included the entire contemporary range of grizzlies in BC, males had higher salmon diets than females (median proportions of 0.41 and 0.04, respectively). High-salmon diets were concentrated in coastal areas for female grizzly bears, whereas males with high-salmon diets in interior areas were restricted to areas near major salmon watersheds. To safeguard this predator–prey association that spans coastal and interior regions, conservation planners and practitioners can consider managing across ecological and jurisdictional boundaries. More broadly, our approach highlights the importance of visualizing spatial patterns of dietary niche variation within populations to characterize ecological associations and inform management.

Citation:

Adams, M.S., C.N. Service, A. Bateman, M. Bourbonnais, K.A. Artelle, T. Nelson, P.C. Paquet, T. Levi, and C.T. Darimont. 2017. Intrapopulation diversity in isotopic niche over landscapes: Spatial patterns inform conservation of bear–salmon systems. Ecosphere 8(6):e01843. 10.1002/ecs2.1843 http://onlinelibrary.wiley.com/wol1/doi/10.1002/ecs2.1843/full 

Intrapopulation diversity in isotopic niche over landscapes Ecosphere, Adams et al 2017 (PDF) 

Figure 5. Spatial patterns of salmon consumption estimated (PDF).

 

 

Side by side maps of density of male and female Grizzly bears

Fig. 5. Spatial patterns of salmon consumption estimated by kernel regression in (a) female and (b) male grizzly bear (Ursus arctos horribilis) diet across British Columbia, between 1995 and 2014. Major salmon-bearing rivers are depicted as gray lines. Areas depicted in white represent regions outside of the models’ spatial extent. Histograms represent frequency of individual bears’ observed median values of proportional salmon consumption.

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