Prokosch Jorinde, Bernitz Zephne, Bernitz Herman, Erni Birgit, Altwegg Res
Department of Mathematical Sciences, Norwegian University of Science and Technology, 7034, Trondheim, Norway.
, Middelburg, 1050, MPU, South Africa.
Oecologia. 2019 Mar;189(3):841-849. doi: 10.1007/s00442-019-04368-2. Epub 2019 Feb 26.
Climate change appears to affect body size of animals whose optimal size in part depends on temperature. However, attribution of observed body size changes to climate change requires an understanding of the selective pressures acting on body size under different temperatures. We examined the link between temperature and body mass in a population of mountain wagtails (Motacilla clara) in KwaZulu-Natal, South Africa, between 1976 and 1999, where temperature increased by 0.18 [Formula: see text]C. The wagtails became lighter by 0.035 g per year. Partitioning this trend, we found that only a small part of the effect (0.009 g/year) was due to individuals losing weight and a large part (0.027 g/year) was due to lighter individuals replacing heavier ones. Only the latter component was statistically significant. Apparently, the wagtails were reacting to selection for reduced weight. Examining survival, we found that selection was temperature-mediated, i.e., lighter individuals survived better under high temperatures, whereas heavier individuals survived better under low temperatures. Our results thus support the hypothesis that temperature drove the decline in body mass in this wagtail population and provides one of the first demonstrations of the selective forces underlying such trends.
气候变化似乎会影响动物的体型大小，而这些动物的最佳体型部分取决于温度。然而，要将观察到的体型变化归因于气候变化，就需要了解在不同温度下作用于体型大小的选择压力。我们研究了1976年至1999年间南非夸祖鲁 - 纳塔尔省一群山地鹡鸰（Motacilla clara）的温度与体重之间的联系，该地温度上升了0.18摄氏度。鹡鸰的体重每年减轻0.035克。剖析这一趋势后，我们发现只有一小部分影响（每年0.009克）是由于个体体重减轻，而一大部分（每年0.027克）是由于较轻的个体取代了较重的个体。只有后一个组成部分具有统计学意义。显然，鹡鸰正在对减轻体重的选择做出反应。在研究存活率时，我们发现选择是由温度介导的，即较轻的个体在高温下存活率更高，而较重的个体在低温下存活率更高。因此，我们的结果支持了温度导致该鹡鸰种群体重下降这一假设，并首次证明了此类趋势背后的选择力量。
