More Like this

1. Diet energy density estimated from isotopes in predator hair associated with survival, habitat, and population dynamics

   https://doi.org/10.1002/eap.2751  

   Rode, Karyn D. ; Taras, Brian D. ; Stricker, Craig A. ; Atwood, Todd C. ; Boucher, Nicole P. ; Durner, George M. ; Derocher, Andrew E. ; Richardson, Evan S. ; Cherry, Seth G. ; Quakenbush, Lori ; et al ( December 2022 , Ecological Applications)

   Sea ice loss is fundamentally altering the Arctic marine environment. Yet there is a paucity of data on the adaptability of food webs to ecosystem change, including predator–prey interactions. Polar bears (Ursus maritimus) are an important subsistence resource for Indigenous people and an apex predator that relies entirely on the under‐ice food web to meet its energy needs. In this study, we assessed whether polar bears maintained dietary energy density by prey switching in response to spatiotemporal variation in prey availability. We compared the macronutrient composition of diets inferred from stable carbon and nitrogen isotopes in polar bear guard hair (primarily representing summer/fall diet) during periods when bears had low and high survival (2004–2016), between bears that summered on land versus pack ice, and between bears occupying different regions of the Alaskan and Canadian Beaufort Sea. Polar bears consumed diets with lower energy density during periods of low survival, suggesting that concurrent increased dietary proportions of beluga whales (Delphinapterus leucas) did not offset reduced proportions of ringed seals (Pusa hispida). Diets with the lowest energy density and proportions from ringed seal blubber were consumed by bears in the western Beaufort Sea (Alaska) during a period when polar bear abundance declined. Intake required to meet energy requirements of an average free‐ranging adult female polar bear was 2.1 kg/day on diets consumed during years with high survival but rose to 3.0 kg/day when survival was low. Although bears that summered onshore in the Alaskan Beaufort Sea had higher‐fat diets than bears that summered on the pack ice, access to the remains of subsistence‐harvested bowhead whales (Balaena mysticetus) contributed little to improving diet energy density. Because most bears in this region remain with the sea ice year round, prey switching and consumption of whale carcasses onshore appear insufficient to augment diets when availability of their primary prey, ringed seals, is reduced. Our results show that a strong predator–prey relationship between polar bears and ringed seals continues in the Beaufort Sea. The method of estimating dietary blubber using predator hair, demonstrated here, provides a new metric to monitor predator–prey relationships that affect individual health and population demographics.

    

   more » « less
2. Increased Arctic sea ice drift alters adult female polar bear movements and energetics

   https://doi.org/10.1111/gcb.13746  

   Durner, George M. ; Douglas, David C. ; Albeke, Shannon E. ; Whiteman, John P. ; Amstrup, Steven C. ; Richardson, Evan ; Wilson, Ryan R. ; Ben‐David, Merav ( June 2017 , Global Change Biology)

   Recent reductions in thickness and extent have increased drift rates of Arctic sea ice. Increased ice drift could significantly affect the movements and the energy balance of polar bears (Ursus maritimus) which forage, nearly exclusively, on this substrate. We used radio‐tracking and ice drift data to quantify the influence of increased drift on bear movements, and we modeled the consequences for energy demands of adult females in the Beaufort and Chukchi seas during two periods with different sea ice characteristics. Westward and northward drift of the sea ice used by polar bears in both regions increased between 1987–1998 and 1999–2013. To remain within their home ranges, polar bears responded to the higher westward ice drift with greater eastward movements, while their movements north in the spring and south in fall were frequently aided by ice motion. To compensate for more rapid westward ice drift in recent years, polar bears covered greater daily distances either by increasing their time spent active (7.6%–9.6%) or by increasing their travel speed (8.5%–8.9%). This increased their calculated annual energy expenditure by 1.8%–3.6% (depending on region and reproductive status), a cost that could be met by capturing an additional 1–3 seals/year. Polar bears selected similar habitats in both periods, indicating that faster drift did not alter habitat preferences. Compounding reduced foraging opportunities that result from habitat loss; changes in ice drift, and associated activity increases, likely exacerbate the physiological stress experienced by polar bears in a warming Arctic.

    

   more » « less
3. High winds and melting sea ice trigger landward movement in a polar bear population of concern

   https://doi.org/10.1002/ecs2.4420  

   Kellner, Annie ; Atwood, Todd C. ; Douglas, David C. ; Breck, Stewart W. ; Wittemyer, George ( February 2023 , Ecosphere)

   Some animal species are responding to climate change by altering the timing of events like mating and migration. Such behavioral plasticity can be adaptive, but it is not always. Polar bears (Ursus maritimus) from the southern Beaufort Sea subpopulation have mostly remained on ice year‐round, but as the climate warms and summer sea ice declines, a growing proportion of the subpopulation is summering ashore. The triggers of this novel behavior are not well understood. Our study uses a parametric time‐to‐event model to test whether biological and/or time‐varying environmental variables thought to influence polar bear movement and habitat selection also drive decisions to swim ashore. We quantified the time polar bears spent occupying offshore sea ice of varying ice concentrations. We evaluated variations in the ordinal date bears moved to land with respect to local environmental conditions such as sea ice concentration and wind across 10 years (2005–2015). Results from our study suggest that storm events (i.e., sustained high wind speeds) may force polar bears from severely degraded ice habitat and catalyze seasonal movements to land. Unlike polar bears long adapted to complete summer ice melt, southern Beaufort Sea bears that summer ashore appear more tolerant of poor‐quality sea ice habitat and are less willing to abandon it. Our findings provide a window into emergent, climatically mediated behavior in an Arctic marine mammal vulnerable to rapid habitat decline.

    

   more » « less
4. Zygomatic arch root position in relation to dietary type in haplorhine primates

   https://doi.org/10.1002/ar.25340  

   Edmonds, Hallie M. ; Daly, E. Susanne ; Smail, Irene E. ( October 2023 , The Anatomical Record)

   The zygomatic root, along with other key craniofacial features, is hypothesized to play a crucial role in strengthening the face in response to stresses and strains related to feeding. As such, it has been cited as indicative of dietary specialization among fossil taxa, although it remains unknown how variable zygomatic arch root position is among living primates, and whether its positioning predicts differences in diet. We test whether primates that consume more mechanically challenging foods possess more anteriorly positioned zygomatic roots compared to those consuming less challenging foods. Zygomatic root position, as defined by the zygomaxillare landmark, was identified and recorded from digital images and physical specimens of adult primate crania. Data were collected from 33 haplorhine species (n = 722). Published data were used to assign species to a dietary type based on patterns of overall consumption along with reliance on especially challenging foods. Pairwise comparisons between mechanically challenging (hard and/or tough) and less mechanically challenging (soft) consumers found significant differences (p < 0.05) in the position of the zygomatic root in 17 of 20 pairs, 11 of which supported the prediction that a more mechanically challenging diet is associated with a more anteriorly placed zygomatic root. PGLS analysis found no significant effect of phylogeny on root position. This suggests that a more anteriorly positioned zygomatic root is useful for identifying dietary specialization in some taxa but is not required for consuming a mechanically challenging diet given that other craniofacial and behavioral factors can facilitate the consumption of such foods.

    

   more » « less
5. How mangabey molar form differs under routine vs. fallback hard-object feeding regimes

   https://doi.org/10.7717/peerj.16534  

   Guatelli-Steinberg, Debbie ; Renteria, Cameron ; Grimm, Jack R. ; Maeret Carpenter, Izabela ; Arola, Dwayne D. ; McGraw, W. Scott ( January 2023 , PeerJ)

   Components of diet known as fallback foods are argued to be critical in shaping primate dental anatomy. Such foods of low(er) nutritional quality are often non-preferred, mechanically challenging resources that species resort to during ecological crunch periods. An oft-cited example of the importance of dietary fallbacks in shaping primate anatomy is the grey-cheeked mangabeyLophocebus albigena. This species relies upon hard seeds only when softer, preferred resources are not available, a fact which has been linked to its thick dental enamel. Another mangabey species with thick enamel, the sooty mangabeyCercocebus atys, processes a mechanically challenging food year-round. That the two mangabey species are both thickly-enameled suggests that both fallback and routine consumption of hard foods are associated with the same anatomical feature, complicating interpretations of thick enamel in the fossil record. We anticipated that aspects of enamel other than its thickness might differ betweenCercocebus atysandLophocebus albigena.We hypothesized that to function adequately under a dietary regime of routine hard-object feeding, the molars ofCercocebus atyswould be more fracture and wear resistant than those ofLophocebus albigena.

   Here we investigated critical fracture loads, nanomechanical properties of enamel, and enamel decussation inCercocebus atysandLophocebus albigena.Molars ofCercopithecus, a genus not associated with hard-object feeding, were included for comparison. Critical loads were estimated using measurements from 2D µCT slices of upper and lower molars. Nanomechanical properties (by nanoindentation) and decussation of enamel prisms (by SEM-imaging) in trigon basins of one upper second molar per taxon were compared.

   Protocone and protoconid critical fracture loads were significantly greater inCercocebus atysthanLophocebus albigenaand greater in both than inCercopithecus. Elastic modulus, hardness, and elasticity index in most regions of the crown were greater inCercocebus atysthan in the other two taxa, with the greatest difference in the outer enamel. All taxa had decussated enamel, but that ofCercocebus atysuniquely exhibited a bundle of transversely oriented prisms cervical to the radial enamel. Quantitative comparison of in-plane and out-of-plane prism angles suggests that decussation in trigon basin enamel is more complex inCercocebus atysthan it is in eitherLophocebus albigenaorCercopithecus cephus. These findings suggest thatCercocebus atysmolars are more fracture and wear resistant than those ofLophocebus albigenaandCercopithecus. Recognition of these differences betweenCercocebus atysandLophocebus albigenamolars sharpens our understanding of associations between hard-object feeding and dental anatomy under conditions of routine vs. fallback hard-object feeding and provides a basis for dietary inference in fossil primates, including hominins.

    

   more » « less