Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, USA.
Department of Natural Resources and Environmental Sciences, University of Illinois Urbana Champaign, Urbana, Illinois, USA.
Glob Chang Biol. 2024 Aug;30(8):e17455. doi: 10.1111/gcb.17455.
Declines in body size can be an advantageous physiological response to warming temperatures, or a result of physiological and nutritional stress. Either way, studies often assume that these climate-induced trait changes have important implications for fitness and demography. We leveraged almost three decades of capture-mark-recapture data of 51 bird species in Panama to examine if body size has changed through time, how sensitive body size is to changes in weather, and if body size impacts population demography. We evaluated two metrics of body size, structural size (wing length), and body condition (residual body mass). Over the study, wing length changed in varying directions for 88% of species (23 decrease, 22 increase), but the effects were weak, and change was only significant for two species. Conversely, body condition declined for 88% of species (45), effects were stronger, and that change was significant for 22% of species (11). This suggests that nutritional stress is likely the cause of changes in body size, not an adaptive response to warming. Precipitation metrics impacted body condition across three of our four feeding guilds, while wing length was only impacted by weather metrics for two guilds. This suggests that body condition is more sensitive to change in weather metrics compared to wing length. Lastly, we found that the impact of changes in body size on survival and recruitment was variable across species, but these relationships were in the opposite direction, ultimately resulting in no change in population growth for all but one species. Thus, while different stages (adult survival and recruitment) of populations may be impacted by body size, populations appear to be buffered from changes. The lack of an effect on population growth rate suggests that populations may be more resilient to changes in body size, with implications for population persistence under expected climate change.
体型缩小可能是对变暖温度的有利生理反应，也可能是生理和营养压力的结果。无论哪种方式，研究通常假设这些由气候引起的特征变化对适应性和种群动态有重要影响。我们利用巴拿马 51 种鸟类近 30 年的捕获-标记-重捕数据，研究了体型是否随时间发生了变化，体型对天气变化的敏感程度，以及体型是否影响种群动态。我们评估了体型的两个指标，结构大小（翼长）和身体状况（剩余体重）。在研究过程中，88%的物种的翼长发生了不同方向的变化（23 种减少，22 种增加），但影响微弱，只有两种物种的变化具有统计学意义。相反，88%的物种的身体状况下降（45 种），影响更强，其中 22%的物种（11 种）的变化具有统计学意义。这表明，身体大小的变化可能是营养压力的结果，而不是对变暖的适应性反应。降水指标影响了我们四个觅食群中的三个的身体状况，而翼长仅受到两个觅食群的天气指标的影响。这表明与翼长相比，身体状况对天气指标的变化更敏感。最后，我们发现，体型变化对存活率和补充率的影响在物种间是不同的，但这些关系是相反的，最终除了一种物种外，所有物种的种群增长率都没有变化。因此，尽管不同阶段（成年存活率和补充率）的种群可能受到体型的影响，但种群似乎受到了缓冲。对种群增长率没有影响表明，种群可能对体型变化更具弹性，这对预期气候变化下的种群生存具有重要意义。
