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Territory acquisition mediates the influence of predators and climate on juvenile red squirrel survival

Citation

Hendrix, Jack G et al. (2021), Territory acquisition mediates the influence of predators and climate on juvenile red squirrel survival, Dryad, Dataset, https://doi.org/10.5061/dryad.q2bvq83g0

Abstract

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.

Methods

A population of red squirrels in the southwest Yukon has been monitored since 1989. We used reproductive and survival data from this population, along with data on predator abundance and weather conditions, to measure survival of juveniles that were alive at the end of the summer in the year of their birth.