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

Abstract

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 km 2 ), 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 km 2 ), 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). Highsalmon 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 predatorprey 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.

Values-led management: the guidance of place-based values in environmental relationships of the past, present, and future

“…This is incongruent with the respectful relationships required by Coastal Peoples. Instead, Coastal Peoples require (and employ) noninvasive approaches for research in the area, with information gleaned through passively collected hair samples without direct interactions or stresses to the bears (Bryan et al 2013, Adams et al 2017; see also Darimont et al 2008 for scat-based approaches). Research on tītī provides a parallel, where strong teachings are in place to protect the mana (honor) and mauri (life force) of the breeding grounds and adult individuals being studied.…”

“…The shift to EBM recognizes that holistic consideration is needed of all components of ecosystems, including people, an important evolution from management focused on individual species, with different and sometimes opposing policies and practices being applied to different elements of ecosystems, e.g., separate management of predators and prey (Darimont et al 2010, Adams et al 2017. However, whereas EBM might recognize the interconnections between people and the environment, its implementation is rarely founded on place-based values (though see Jones et al 2010, Kahui and Richards 2014, and Marine Planning Partnership Initiative 2015 for discussion on intersection of values-led management and EBM).…”

The primacy of bears as seed dispersers in salmon‐bearing ecosystems

“…, , Adams et al. ). However, extensive berry consumption by competitively dominant brown bears, which has been demonstrated in a system without black bears (Willson and Gende ), would cast doubt on resource partitioning as the mechanism of Ursid coexistence.…”

“…Where brown and black bears are sympatric in salmon-rich systems, competitively dominant brown bears exclude black bears from accessing salmon (Belant et al 2006, Levi et al 2015, leaving black bears to primarily consume berries and green vegetation (Belant et al 2006, 2010, Adams et al 2017). However, extensive berry consumption by competitively dominant brown bears, which has been demonstrated in a system without black bears (Willson and Gende 2004), would cast doubt on resource partitioning as the mechanism of Ursid coexistence.…”

Synchronous timing of food resources triggers bears to switch from salmon to berries

“…How bear behavior and social dominance is altered by synchronization of key foods is unclear but an important topic for future research given that subdominant bears are especially important for moving salmon carcasses into the adjacent riparian zone; subdominant bears often haul salmon carcasses into the forest to avoid dominant bears in the stream channel (9). Moreover, male bears tend to have a more salmon-rich diet than females (10), possibly because females with spring cubs actively avoid salmon streams to reduce the risk of infanticide (11). If females switch from stream salmon to elderberry earlier than males, this might partially explain the results of previous studies (10,11) and have consequences for cub growth and survival, particularly if cubs are more protein-limited than adult bears.…”