Long-term studies of wild animals provide the opportunity to investigate how phenotypic plasticity is used to cope with environmental fluctuations, and how the relationships between phenotypes and fitness can be dependent upon the ecological context. Most previous studies have only investigated life history plasticity in response to changes in temperature, yet wild animals often experience multiple environmental fluctuations simultaneously. This requires field experiments to decouple which ecological factor induces plasticity in fitness-relevant traits to better understand their population-level responses to those environmental fluctuations. For the past 32 years, we have conducted a long-term integrative study of individually marked North American red squirrels (Tamiasciurus hudsonicus Erxleben) in the Yukon, Canada. We have used multi-year field experiments to examine the physiological and life history responses of individual red squirrels to fluctuations in food abundance and conspecific density. Our long-term observational study and field experiments show that squirrels can anticipate increases in food availability and density, thereby decoupling the usual pattern where animals respond to, rather than anticipate, an ecological change. As in many other study systems, ecological factors that can induce plasticity (such as food and density) co-vary. However, our field experiments that manipulate food availability and social cues of density (frequency of territorial vocalizations) indicate that increases in social (acoustic) cues of density in the absence of additional food can induce similar life history plasticity, as does experimental food supplementation. Changes in the levels of metabolic hormones (glucocorticoids) in response to variation in food and density are one mechanism that seems to induce this adaptive life history plasticity. Although we have not yet investigated the energetic response of squirrels to elevated density or its association with life history plasticity, energetics research in red squirrels has overturned several standard pillars of knowledge in physiological ecology. We show how a tractable model species combined with integrative studies can reveal how animals cope with resource fluctuations through life history plasticity.

中文翻译：

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使用野外实验将食物和密度对野生动物生活史可塑性的影响脱钩：来自坐在尾巴阴影下的北美红松鼠的洞察力

对野生动物的长期研究提供了研究表型可塑性如何用于应对环境波动以及表型与健康之间的关系如何依赖于生态环境的机会。大多数以前的研究只研究了对温度变化的生命史可塑性，但野生动物经常同时经历多种环境波动。这需要现场实验来解耦哪些生态因素会导致适应性相关性状的可塑性，以更好地了解它们对这些环境波动的种群水平反应。在过去的 32 年中，我们对加拿大育空地区的单独标记的北美红松鼠 (Tamiasciurus hudsonicus Erxleben) 进行了长期综合研究。我们使用多年的现场实验来检查个体红松鼠对食物丰度和同种密度波动的生理和生活史反应。我们的长期观察研究和现场实验表明，松鼠可以预测食物供应量和密度的增加，从而使动物对生态变化做出反应而不是预期的通常模式脱钩。与许多其他研究系统一样，可引起可塑性的生态因素（例如食物和密度）会共同变化。然而，我们操纵食物可用性和密度的社会线索（领土发声频率）的现场实验表明，在没有额外食物的情况下，密度的社会（声学）线索的增加可以引起类似的生活史可塑性，实验性食物补充也是如此。响应于食物和密度变化的代谢激素（糖皮质激素）水平的变化似乎是诱导这种适应性生活史可塑性的一种机制。尽管我们还没有研究松鼠对密度升高的能量反应或其与生活史可塑性的关联，但红松鼠的能量学研究已经推翻了生理生态学中的几个标准知识支柱。我们展示了一个易于处理的模型物种如何结合综合研究来揭示动物如何通过生活史可塑性来应对资源波动。尽管我们还没有研究松鼠对密度升高的能量反应或其与生活史可塑性的关联，但红松鼠的能量学研究已经推翻了生理生态学中的几个标准知识支柱。我们展示了一个易于处理的模型物种如何结合综合研究来揭示动物如何通过生活史可塑性来应对资源波动。尽管我们还没有研究松鼠对密度升高的能量反应或其与生活史可塑性的关联，但红松鼠的能量学研究已经推翻了生理生态学中的几个标准知识支柱。我们展示了一个易于处理的模型物种如何结合综合研究来揭示动物如何通过生活史可塑性来应对资源波动。