For ungulates and other long-lived species, life-history theory predicts that nutritional reserves are allocated to reproduction in a state-dependent manner because survival is highly conserved. Further, as per capita food abundance and nutritional reserves decline (i.e., density dependence intensifies), reproduction and recruitment become increasingly sensitive to weather. Thus, the degree to which weather influences vital rates should be associated with proximity to nutritional carrying capacity—a notion that we refer to as the Nutritional Buffer Hypothesis. We tested the Nutritional Buffer Hypothesis using six moose (Alces alces) populations that varied in calf recruitment (33–69 calves/100 cows). We predicted that populations with high calf recruitment were nutritionally buffered against the effects of unfavorable weather, and thus were below nutritional carrying capacity. We applied a suite of tools to quantify habitat and nutritional condition of each population and found that increased browse condition, forage quality, and body fat were associated with increased pregnancy and calf recruitment, thereby providing multiple lines of evidence that declines in calf recruitment were underpinned by resource limitation. From 2001 to 2015, recruitment was more sensitive to interannual variation in weather (e.g., winter severity, drought) and plant phenology (e.g., duration of spring) for populations with reduced browse condition, forage quality, and body fat, suggesting these populations lacked the nutritional reserves necessary to buffer demographic performance against the effects of unfavorable weather. Further, average within-population calf recruitment was determined by regional climatic variation, suggesting that the pattern of reduced recruitment near the southern range boundary of moose stems from an interaction between climate and resource limitation. When coupled with information on habitat, nutrition, weather, and climate, life-history theory provides a framework to estimate nutritional limitation, proximity to nutritional carrying capacity, and impacts of climate change for ungulates.

中文翻译：

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生活史理论提供了一个检测资源限制的框架：营养缓冲假说的检验

对于有蹄类动物和其他长寿物种，生活史理论预测营养储备以依赖于状态的方式分配给繁殖，因为生存是高度保守的。此外，随着人均食物丰度和营养储备下降（即密度依赖性加剧），繁殖和补充对天气越来越敏感。因此，天气对生命率的影响程度应该与营养承载能力的接近程度相关——我们将这一概念称为营养缓冲假说。我们使用六只驼鹿 ( Alces alces) 小牛募集数量不同的种群（33-69 头小牛/100 头奶牛）。我们预测，小牛补充率高的种群在营养上缓冲了不利天气的影响，因此低于营养承载能力。我们应用了一套工具来量化每个种群的栖息地和营养状况，发现增加的采食条件、饲料质量和体脂与增加怀孕和小牛补充有关，从而提供了多种证据表明小牛补充下降是基础由于资源限制。从 2001 年到 2015 年，对于采食条件、草料质量和体脂较低的种群，招募对天气（例如，冬季严重程度、干旱）和植物物候（例如，春季持续时间）的年际变化更为敏感，表明这些人口缺乏必要的营养储备来缓冲不利天气的影响。此外，种群内小牛的平均招募率由区域气候变化决定，这表明驼鹿南部范围边界附近招募减少的模式源于气候和资源限制之间的相互作用。当结合栖息地、营养、天气和气候信息时，生活史理论提供了一个框架来估计营养限制、接近营养承载能力以及气候变化对有蹄类动物的影响。种群内小牛的平均补充量由区域气候变化决定，这表明驼鹿南部范围边界附近的补充量减少模式源于气候和资源限制之间的相互作用。当结合栖息地、营养、天气和气候信息时，生活史理论提供了一个框架来估计营养限制、接近营养承载能力以及气候变化对有蹄类动物的影响。种群内小牛的平均补充量由区域气候变化决定，这表明驼鹿南部范围边界附近的补充量减少模式源于气候和资源限制之间的相互作用。当结合栖息地、营养、天气和气候信息时，生活史理论提供了一个框架来估计营养限制、接近营养承载能力以及气候变化对有蹄类动物的影响。