Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Department of Biology, Sweet Briar College, Sweet Briar, VA, 24595, USA.
Glob Chang Biol. 2017 Jul;23(7):2565-2576. doi: 10.1111/gcb.13589. Epub 2017 Jan 3.
Addressing population declines of migratory insects requires linking populations across different portions of the annual cycle and understanding the effects of variation in weather and climate on productivity, recruitment, and patterns of long-distance movement. We used stable H and C isotopes and geospatial modeling to estimate the natal origin of monarch butterflies (Danaus plexippus) in eastern North America using over 1000 monarchs collected over almost four decades at Mexican overwintering colonies. Multinomial regression was used to ascertain which climate-related factors best-predicted temporal variation in natal origin across six breeding regions. The region producing the largest proportion of overwintering monarchs was the US Midwest (mean annual proportion = 0.38; 95% CI: 0.36-0.41) followed by the north-central (0.17; 0.14-0.18), northeast (0.15; 0.11-0.16), northwest (0.12; 0.12-0.16), southwest (0.11; 0.08-0.12), and southeast (0.08; 0.07-0.11) regions. There was no evidence of directional shifts in the relative contributions of different natal regions over time, which suggests these regions are comprising the same relative proportion of the overwintering population in recent years as in the mid-1970s. Instead, interannual variation in the proportion of monarchs from each region covaried with climate, as measured by the Southern Oscillation Index and regional-specific daily maximum temperature and precipitation, which together likely dictate larval development rates and food plant condition. Our results provide the first robust long-term analysis of predictors of the natal origins of monarchs overwintering in Mexico. Conservation efforts on the breeding grounds focused on the Midwest region will likely have the greatest benefit to eastern North American migratory monarchs, but the population will likely remain sensitive to regional and stochastic weather patterns.
解决迁徙昆虫数量下降的问题需要将不同年度周期的种群联系起来，并了解天气和气候变化对生产力、补充和长距离迁移模式的影响。我们使用稳定的 H 和 C 同位素和地理空间模型，利用近 40 年来在墨西哥越冬地收集的 1000 多只帝王蝶（Danaus plexippus），估计东北美帝王蝶的出生地。使用多项回归来确定哪些与气候相关的因素可以最好地预测六个繁殖区的出生地随时间的变化。产生越冬帝王蝶比例最大的地区是美国中西部（平均年比例为 0.38；95%置信区间：0.36-0.41），其次是中北部（0.17；0.14-0.18）、东北部（0.15；0.11-0.16）、西北部（0.12；0.12-0.16）、西南部（0.11；0.08-0.12）和东南部（0.08；0.07-0.11）地区。没有证据表明不同出生地相对贡献随时间的变化有方向性，这表明这些地区在近年来构成越冬种群的相对比例与 20 世纪 70 年代中期相同。相反，每个地区的帝王蝶比例的年际变化与气候相关，由南方涛动指数和区域特定的日最高温度和降水来衡量，这些因素共同决定了幼虫发育速度和食物植物状况。我们的研究结果提供了对帝王蝶在墨西哥越冬出生地的预测因素的首次稳健的长期分析。在繁殖地进行的保护工作集中在中西部地区，这可能对东北美迁徙的帝王蝶最有益，但该种群可能仍然对区域和随机天气模式敏感。
