Emigration effects on estimates of age- and sex-specific survival of two sciurids,Ecology and Evolution

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Emigration effects on estimates of age- and sex-specific survival of two sciurids
Ecology and Evolution ( IF 2.3 ) Pub Date : 2022-04-23 , DOI: 10.1002/ece3.8833
Matthew J Weldy ₁ , Damon B Lesmeister _{1,

2} , Clinton W Epps ₂

Affiliation

Age- and sex-specific survival estimates are crucial to understanding important life history characteristics, and variation in these estimates can be a key driver of population dynamics. When estimating survival using Cormack–Jolly–Seber (CJS) models, emigration is typically unknown but confounded with apparent survival. Consequently, especially for populations or age classes with high dispersal rates, apparent survival estimates are often biased low and temporal patterns in survival might be masked when site fidelity varies temporally. We used 9 years of annual mark–recapture data to estimate age-, sex-, and time-specific apparent survival of Humboldt's flying squirrels (Glaucomys oregonensis) and Townsend's chipmunks (Neotamias townsendii). For Humboldt's flying squirrels, these estimates support a small body of research investigating potential variation in survival among age and sex classes, but age- and sex-specific survival has not been evaluated for Townsend's chipmunks. We also quantified the effects of age- and sex-specific emigration on confounded estimates of apparent survival. Our estimates of juvenile flying squirrel survival were high relative to other small mammal species and estimates for both species were variable among years. We found survival differed moderately among age and sex classes for Humboldt's flying squirrels, but little among age and sex classes for Townsend's chipmunks, and that the degree to which emigration confounded apparent survival estimates varied substantially among years. Our results demonstrate that emigration can influence commonly used estimates of apparent survival. Unadjusted estimates confounded the interpretation of differences in survival between age and sex classes and masked potential temporal patterns in survival because the magnitude of adjustment varied among years. We conclude that apparent survival estimators are robust during some time periods; however, when emigration rates vary in time, the effects of emigration should be carefully considered and accounted for.

中文翻译：

移民对两种松鼠科动物年龄和性别特异性生存估计的影响

特定年龄和性别的生存估计对于了解重要的生活史特征至关重要，这些估计的变化可能是人口动态的关键驱动因素。当使用 Cormack-Jolly-Seber (CJS) 模型估计生存率时，移民通常是未知的，但与表观生存率相混淆。因此，特别是对于具有高扩散率的人群或年龄层，表观生存估计通常偏低，并且当站点保真度随时间变化时，生存的时间模式可能会被掩盖。我们使用了 9 年的年度标记-重新捕获数据来估计洪堡飞鼠 ( Glaucomomys oregonensis ) 和汤森花栗鼠 ( Neotamias Townsendii ) 的年龄、性别和时间特定的表观存活率。对于洪堡飞鼠来说，这些估计支持了一小部分调查年龄和性别类别之间生存率潜在差异的研究，但尚未对汤森花栗鼠的年龄和性别特异性生存率进行评估。我们还量化了特定年龄和性别的移民对表观生存的混杂估计的影响。相对于其他小型哺乳动物物种，我们对幼年鼯鼠存活率的估计较高，并且对这两个物种的估计多年来都有所变化。我们发现，洪堡鼯鼠的年龄和性别类别之间的生存率存在适度差异，但汤森花栗鼠的年龄和性别类别之间的生存率差异不大，而且移民对表观生存率估计的干扰程度在不同年份之间存在很大差异。我们的结果表明，移民可以影响常用的表观生存估计。未经调整的估计混淆了对年龄和性别类别之间生存差异的解释，并掩盖了生存的潜在时间模式，因为调整的幅度因年份而异。我们得出的结论是，表观生存估计量在某些时间段内是稳健的；然而，当移民率随时间变化时，应仔细考虑和解释移民的影响。

更新日期：2022-04-24

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