Mjaaseth Ragnhild R, Hagen Snorre B, Yoccoz Nigel G, Ims Rolf A
Department of Biology, University of Tromsø, 9037, Tromsø, Norway.
Oecologia. 2005 Aug;145(1):53-65. doi: 10.1007/s00442-005-0089-1. Epub 2005 Jul 8.
The two forest-defoliating geometrid moth species Operophtera brumata and Epirrita autumnata are known to exhibit different altitudinal distribution patterns in northern birch forests. One possible explanation for this is that altitudinal climatic variation differentially affects the performance of two species through mismatching larval and host plant phenology. We explored this hypothesis by investigating the relationship between larval phenology and leaf phenology of Betula pubescens, which is the main host plant of both moth species, along ten replicate altitudinal transects during two springs with contrasting climate in northern Norway. There was a distinct monotonous cline in host plant phenology with increasing altitude in both years of the study, but the development of the leaves were generally 14 days later in the first of the 2 years due to cold spring weather. We found that larval development of both species closely tracked host plant leaf phenology independent of altitude and year. However, at the time of sampling, E. autumnata was approximately one instar ahead of O. brumata at all altitudes, probably reflecting that E. autumnata has faster early instar growth than O. brumata. The abundance of O. brumata was lowest at the altitudinal forest-line, while E. autumnata was lowest near sea level. Our results do not indicate that the altitudinal distribution patterns of the two moth species is due to any phenological mismatch between larval and host plant phenology. We suggest rather that natural enemies at low altitudes limit larval survival and thus abundance of E. autumnata, while an early onset of winter at the forest limit reduces survival of late eclosing adults of O. brumata.
已知两种食叶尺蛾Operophtera brumata和Epirrita autumnata在北方桦树林中呈现出不同的海拔分布模式。对此一种可能的解释是，海拔气候差异通过幼虫与寄主植物物候不匹配，对这两个物种的表现产生不同影响。我们通过在挪威北部两个气候不同的春季沿着十个重复的海拔样带，研究这两种尺蛾的主要寄主植物欧洲桦的幼虫物候与叶片物候之间的关系，来探究这一假设。在研究的两年中，寄主植物物候均随海拔升高呈现出明显的单调梯度变化，但由于春季寒冷，第一年叶片发育普遍推迟了14天。我们发现，两个物种的幼虫发育都紧密跟踪寄主植物叶片物候，与海拔和年份无关。然而，在采样时，E. autumnata在所有海拔高度上比O. brumata大约早一个龄期，这可能反映出E. autumnata早期龄期的生长速度比O. brumata快。O. brumata的数量在海拔森林线处最低，而E. autumnata在海平面附近最低。我们的结果并未表明这两种尺蛾的海拔分布模式是由于幼虫与寄主植物物候之间的任何物候不匹配所致。我们认为，低海拔地区的天敌限制了幼虫的存活，从而限制了E. autumnata的数量，而森林界限处冬季的提前到来降低了O. brumata晚期羽化成虫的存活率。
