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Hendrix, Jack G; Fisher, David; Martinig, April; Boutin, Stan; Dantzer, Ben; Lane, Jeffrey; McAdam, Andrew 2021-03-06 <p>1) Juvenile survival to first breeding is a key life history stage for all taxa. Survival through this period can be particularly challenging when it can coincide with harsh environmental conditions such as a winter climate or food scarcity, leading to highly variable cohort survival. However, the small size and dispersive nature of juveniles generally makes studying their survival more difficult. 2) In territorial species, a key life history event is the acquisition of a territory. A territory is expected to enhance survival, but how it does so is not often identified. We tested how the timing of territory acquisition influenced the winter survival of juvenile North American red squirrels Tamiasciurus hudsonicus, hereafter red squirrels, and how the timing of this event mediated sources of mortality. We hypothesized that securing a territory prior to when food resources become available would reduce juvenile susceptibility to predation and climatic factors over winter. 3) Using 27 years of data on the survival of individually-marked juvenile red squirrels, we tested how the timing of territory acquisition influenced survival, whether the population density of red squirrel predators and mean temperature over winter were related to individual survival probability, and if territory ownership mediated these effects. 4) Juvenile red squirrel survival was lower in years of high predator abundance and in colder winters. Autumn territory owners were less susceptible to lynx Lynx canadensis, and possibly mustelid Mustela and Martes spp., predation. Autumn territory owners had lower survival in colder winters, but surprisingly non-owners had higher survival in cold winters. 5) Our results show how the timing of a life history event like territory acquisition can directly affect survival and also mediate the effects of biotic and abiotic factors later in life. This engenders a better understanding of the fitness consequences of the timing of key life history events.</p>
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Menzies, Allyson; Studd, Emily; Majchrzak, Yasmine; Peers, Michael; Boutin, Stan; Dantzer, Ben; Lane, Jeffrey; McAdam, Andrew; Humphries, Murray 2020-07-31 <ol> <li style="margin-bottom:12px;">Organisms survive environmental variation by combining homeostatic regulation of critical states with allostatic variation of other traits, and species differences in these responses can contribute to coexistence in temporally-variable environments.</li> <li style="margin-bottom:12px;">In this paper, we simultaneously record variation in three functional traits – body temperature (Tb), heart rate, and activity - in relation to three forms of environmental variation – air temperature (Ta), photoperiod, and experimentally-manipulated resource levels – in free-ranging snowshoe hares and North American red squirrels to characterize distinctions in homeotherm responses to the extreme conditions of northern boreal winters.</li> <li style="margin-bottom:12px;">Hares and squirrels differed in the level and precision of Tb regulation, but also in the allostatic pathways necessary to maintain thermal homeostasis. Hares demonstrated a stronger metabolic pathway (through heart rate variation reflective of the thermogenesis), while squirrels demonstrated a stronger behavioral pathway (through activity variation that minimizes cold exposure).</li> <li style="margin-bottom:12px;">As intermediate-sized, winter-active homeotherms, hares and squirrels share many functional attributes, yet, through the integrated monitoring of multiple functional traits in response to shared environmental variation, our study reveals many pairwise species differences in homeostatic and allostatic traits, that both define and are defined by the natural history, functional niches, and coexistence of sympatric species.</li> </ol> https://creativecommons.org/publicdomain/zero/1.0/
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Petrullo, Lauren; Dantzer, Ben; McAdam, Andrew; Boutin, Stan; Lane, Jeffrey E. 2023 Included in this repository are three (3) dataset .csv files. The first is the main dataset for all females included in the study (emt_data_pub.csv). The second is the main dataset for all offspring/pups born to the females from Dataset 1 included in the study (emt_offspring_dataset.csv). The third is a subset of the first dataset including only females for who we had total cache size estimates for (cache_size_pub.csv). Please see the Materials and Methods section of the supplementary material for this manuscript for detail on statistical methods and variable descriptions. Additionally included in this repository is a single R script (emt_code.R) containing the necessary code and calls to the relevant tables in order to generate the data presented in the manuscript. https://creativecommons.org/licenses/by/4.0/legalcode

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