Theriot Miranda K, Olson Link E, Lanier Hayley C
Sam Noble Oklahoma Museum of Natural History, School of Biological Sciences, University of Oklahoma, Norman, OK 73072, United States.
University of Alaska Museum, University of Alaska Fairbanks, Fairbanks, AK 99775, United States.
J Mammal. 2024 Mar 7;105(3):512-523. doi: 10.1093/jmammal/gyae005. eCollection 2024 Jun.
Shifts in mean body size coinciding with environmental change are well documented across animal species and populations, serving as a widespread and complex indicator of climate-change response. In mammal research, identifying and disentangling the potential drivers of these trends (e.g., thermoregulation, resource availability) is hindered by treating adult size as fixed, ignoring morphological changes that occur throughout life in many species. However, observed population-level size trends may reflect underlying shifts in age structure (i.e., change in the proportion of older, potentially larger individuals in the population). Here, we assessed the role of age structure by explicitly evaluating age as a contributor to temporal variation in skull size (a proxy for body size) in 2 carnivorans, Canadian Lynx () and American Marten (). Using a series of linear and nonlinear models, we tested age in years (determined by cementum-layer analysis) as a predictor of skull size alongside other factors previously proposed to be important drivers of body-size trends, including population density for lynx and growing season conditions for martens. In both species, age was a significant predictor of skull size indicating a rapid year-to-year increase in young adult size that diminished in later adulthood. However, temporal shifts in age structure alone did not explain the observed changes in size over time, indicating that age structure acts in concert with other as-yet unidentified factors to drive body-size change. By explicitly evaluating the role of age, we can both refine models of temporal body-size trends and gain insights into size change as a signal of underlying demographic shifts-such as age-specific survivorship-providing a more holistic understanding of how mammals are responding to climate change.
在动物物种和种群中，平均体型的变化与环境变化相吻合，这在大量文献中都有记载，是气候变化响应的一个广泛而复杂的指标。在哺乳动物研究中，将成年体型视为固定不变，忽略了许多物种一生中发生的形态变化，这阻碍了对这些趋势潜在驱动因素（如体温调节、资源可用性）的识别和梳理。然而，观察到的种群水平体型趋势可能反映了年龄结构的潜在变化（即种群中年龄较大、可能体型较大的个体比例的变化）。在这里，我们通过明确评估年龄对两种食肉动物——加拿大猞猁（Lynx canadensis）和美洲貂（Martes americana）头骨大小（体型的一个替代指标）随时间变化的贡献，来评估年龄结构的作用。我们使用一系列线性和非线性模型，将以年为单位的年龄（通过牙骨质层分析确定）作为头骨大小的预测因子进行测试，同时考虑其他先前被认为是体型趋势重要驱动因素的因素，包括猞猁的种群密度和貂的生长季节条件。在这两个物种中，年龄都是头骨大小的一个重要预测因子，表明成年早期体型逐年快速增加，而在成年后期则有所减少。然而，仅年龄结构的时间变化并不能解释观察到的体型随时间的变化，这表明年龄结构与其他尚未确定的因素共同作用，推动体型变化。通过明确评估年龄的作用，我们既能完善体型随时间变化趋势的模型，又能深入了解体型变化作为潜在人口结构变化信号（如特定年龄的存活率）的情况，从而更全面地理解哺乳动物对气候变化的反应。
