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 degrees C. The wagtails became lighter by 0.035g per year. Partitioning this trend, we found that only a small part of the effect (0.009g/year) was due to individuals losing weight and a large part (0.027g/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.
1.Norwegian Univ Sci & Technol, Dept Math Sci, N-7034 Trondheim, Norway 2.MPU, ZA-1050 Middelburg, South Africa 3.Univ Pretoria, Sch Dent, Dept Oral Pathol & Oral Biol, ZA-0001 Pretoria, South Africa 4.Univ Cape Town, Dept Stat Sci, Stat Ecol Environm & Conservat, ZA-7701 Rondebosch, South Africa 5.Univ Cape Town, African Climate & Dev Initiat, ZA-7701 Rondebosch, South Africa
Recommended Citation:
Prokosch, Jorinde,Bernitz, Zephne,Bernitz, Herman,et al. Are animals shrinking due to climate change? Temperature-mediated selection on body mass in mountain wagtails[J]. OECOLOGIA,2019-01-01,189(3):841-849