Abstract：
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.
摘要：
体型的下降可能是对温度升高的有利生理反应，或者生理和营养压力的结果。无论哪种方式,研究通常认为，这些气候引起的性状变化对适应性和人口学具有重要意义。我们利用了巴拿马51种鸟类近三十年的捕获-标记-再捕获数据来检查体型是否随着时间的推移而发生变化，体型对天气变化有多敏感，以及体型是否会影响人口统计。我们评估了身体大小的两个指标，结构尺寸（机翼长度），和身体状况（残余体重）。在研究中，88%的物种的机翼长度在不同方向上变化(减少23，22增加），但是效果很弱，变化只对两个物种有意义。相反，88%的物种(45)的身体状况下降，效果更强，这种变化对22%的物种来说是显著的(11)。这表明营养压力可能是身体大小变化的原因，不是对变暖的适应性反应。降水指标影响了我们四个饲喂行会中的三个的身体状况，而机翼长度仅受两个行会的天气指标影响。这表明与机翼长度相比，身体状况对天气指标的变化更敏感。最后,我们发现体型的变化对生存和招募的影响在不同物种之间是可变的，但是这些关系是相反的，最终导致除一个物种外所有物种的种群增长没有变化。因此，虽然人口的不同阶段（成人生存和招募）可能会受到体型的影响，人口似乎被缓冲了变化。对人口增长率缺乏影响表明，人口可能对体型变化更具弹性，对预期气候变化下的人口持久性有影响。
