Delayed spring onset drives declines in abundance and recruitment in a mountain ungulate

Rattenbury, Kumi L.; Schmidt, Joshua H.; Swanson, David K.; Borg, Bridget L.; Mangipane, Buck A.; Sousanes, Pamela J.

doi:10.1002/ecs2.2513

Cited by 21 publications

(33 citation statements)

References 60 publications

(118 reference statements)

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“…Bear body size and productivity were generally higher in this subarea as well (Hilderbrand et al 2019 b ), suggesting that greater access to food resources (e.g., large spawning concentrations of chum salmon ( Oncorhynchus keta ) in the lower portions of the Noatak River [Menard et al 2020], beached marine mammals, and a suite of ungulate prey species) may afford a partial explanation. Estimates from the other 3 subareas were similar to those reported for other interior Alaska populations, possibly a function of ≥1 factors, including limited food resources (i.e., limited salmon and lower ungulate densities in the Upper Noatak and Gates of the Arctic; Miller et al 1997, Westing 2012, Rattenbury et al 2018), limited reproductive output in Gates of the Arctic (Hilderbrand et al 2019 a , b ), shorter growing seasons, and higher harvest in the case of the Seward Peninsula.…”

Section: Discussionsupporting

confidence: 66%

Brown Bear Density and Estimated Harvest Rates in Northwestern Alaska

et al. 2021

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Human‐caused mortality in general, and unregulated hunting in particular, have been implicated in reductions in brown bear (Ursus arctos) populations throughout much of their range. In northwestern Alaska, USA, bear densities have not been assessed in 20 years while harvest regulations have been liberalized, raising concerns that broad undetected population declines might occur. We used a modified mark‐resight approach to estimate brown bear density during 2005–2018 in 4 subareas throughout the region. We also summarized harvest information for each subarea and used our survey results to estimate harvest rates. We estimated densities for independent bears assuming constant or heterogeneous probabilities of detection and occurrence. We present the results of the constant model for more direct comparison with past work and the heterogeneity model results to provide estimates of density that are less likely to be negatively biased. Using the constant model, we estimated the density of independent bears was 17.0, 49.2, 24.9, and 19.4/1,000 km2 on portions of the Seward Peninsula, the lower Noatak River, the upper Noatak River, and Gates of the Arctic National Park and Preserve, respectively. These estimates are broadly similar to those from past work in interior and northwestern Alaska, with the exception of the lower Noatak River subarea where our estimates are the highest reported for a bear population in northern Alaska. We estimated that the harvest rate on the Seward Peninsula was approximately 5.2% or 7.7% on average, depending upon the model used. In the remaining areas, we estimated annual harvest rates were <2.5%, well within sustainability guidelines from past work. Overall, our results suggest that brown bear densities are similar or somewhat higher than in the past in much of northwestern Alaska and that current harvest rates are sustainable in most areas, except perhaps the Seward Peninsula. Ongoing survey work will be useful for further evaluating the assumptions of the modified mark‐resight survey approach, assessing population trajectory, and determining the effect of harvest on brown bear populations. © 2021 The Wildlife Society.

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Section: Discussionsupporting

confidence: 66%

Brown Bear Density and Estimated Harvest Rates in Northwestern Alaska

et al. 2021

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“…Recent work has suggested that climate can exert a strong influence on the behavior and demography of Dall’s sheep, but many questions remain. Across Alaska, a decline in recruitment of lambs and survival of adults is strongly affected by spring weather, and the magnitude of the effect varies across latitudes [ 32 – 34 ]. In the Northern Richardson Mountains of the Yukon in Canada, multiple factors such as potential competition for resources with other herbivores, predation, and emerging diseases could be contributing to observed population declines, however, the effects of documented increases in temperature and precipitation related to climate change remain unknown [ 30 ].…”

Section: Introductionmentioning

confidence: 99%

Habitat selection by Dall’s sheep is influenced by multiple factors including direct and indirect climate effects

et al. 2021

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Arctic and boreal environments are changing rapidly, which could decouple behavioral and demographic traits of animals from the resource pulses that have shaped their evolution. Dall’s sheep (Ovis dalli dalli) in northwestern regions of the USA and Canada, survive long, severe winters and reproduce during summers with short growing seasons. We sought to understand the vulnerability of Dall’s sheep to a changing climate in Lake Clark National Park and Preserve, Alaska, USA. We developed ecological hypotheses about nutritional needs, security from predators, energetic costs of movement, and thermal shelter to describe habitat selection during winter, spring, and summer and evaluated habitat and climate variables that reflected these hypotheses. We used the synoptic model of animal space use to estimate parameters of habitat selection by individual females and calculated likelihoods for ecological hypotheses within seasonal models. Our results showed that seasonal habitat selection was influenced by multiple ecological requirements simultaneously. Across all seasons, sheep selected steep rugged areas near escape terrain for security from predators. During winter and spring, sheep selected habitats with increased forage and security, moderated thermal conditions, and lowered energetic costs of movement. During summer, nutritional needs and security influenced habitat selection. Climate directly influenced habitat selection during the spring lambing period when sheep selected areas with lower snow depths, less snow cover, and higher air temperatures. Indirectly, climate is linked to the expansion of shrub/scrub vegetation, which was significantly avoided in all seasons. Dall’s sheep balance resource selection to meet multiple needs across seasons and such behaviors are finely tuned to patterns of phenology and climate. Direct and indirect effects of a changing climate may reduce their ability to balance their needs and lead to continued population declines. However, several management approaches could promote resiliency of alpine habitats that support Dall’s sheep populations.

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“…Evidence of the effects of weather and climate on wildlife populations includes mortality due to extreme events (e.g., Rattenbury et al 2018), reduction in food resources (e.g., Rutz and Bijlsma 2006;Schmidt et al 2018a, b), and phenological mismatches (Stenseth and Mysterud 2002;Durant et al 2007;Post and Forchhammer 2007). Our findings further suggest that the effects of reductions in resource access can be nuanced and interconnected, thereby playing an important role in determining how variation in weather conditions can influence population dynamics.…”

Section: Discussionmentioning

confidence: 52%

“…Variation in weather and climate influence primary productivity and are important drivers of population dynamics in a variety of vertebrate taxa including ungulates (Post and Stenseth 1999;Rattenbury et al 2018), passerines (Sillett et al 2000;Boelman et al 2017), seabirds (Thompson and Ollason 2001), and raptors (Franklin et al 2000;Fairhurst and Bechard 2005;Glenn et al 2010). The effects of weather and climate can be both direct and indirect, potentially complicating a mechanistic understanding of systems.…”

Section: Introductionmentioning

confidence: 99%

Direct and indirect effects of temperature and prey abundance on bald eagle reproductive dynamics

2019

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Understanding the mechanisms by which populations are regulated is critical for predicting the effects of large-scale perturbations. While discrete mortality events provide clear evidence of direct impacts, indirect pathways are more difficult to assess but may play important roles in population and ecosystem dynamics. Here, we use multi-state occupancy models to analyze a long-term dataset on nesting bald eagles in south-central Alaska with the goal of identifying both direct and indirect mechanisms influencing reproductive output in this apex predator. We found that the probabilities of both nest occupancy and success were higher in the portion of the study area where water turbidity was low, supporting the hypothesis that access to aquatic prey is a critical factor limiting the reproductive output of eagles in this system. As expected, nest success was also positively related to salmon abundance; however, the negative effect of spring warmth suggested that access to salmon resources is indirectly diminished in warm springs as a consequence of increased glacial melt. Together, these findings reveal complex interrelationships between a critical prey resource and large-scale weather and climate processes which likely alter the accessibility of resources rather than directly affecting resource abundance. While important for understanding bald eagle reproductive dynamics in this system specifically, our results have broader implications that suggest complex interrelationships among system components.

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Delayed spring onset drives declines in abundance and recruitment in a mountain ungulate

Cited by 21 publications

References 60 publications

Brown Bear Density and Estimated Harvest Rates in Northwestern Alaska

Brown Bear Density and Estimated Harvest Rates in Northwestern Alaska

Habitat selection by Dall’s sheep is influenced by multiple factors including direct and indirect climate effects

Direct and indirect effects of temperature and prey abundance on bald eagle reproductive dynamics

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