Dynamics of two Montana grasshopper populations: relationships among weather, food abundance and intraspecific competition
Dynamics of two Montana grasshopper populations: relationships among weather, food abundance and intraspecific competition
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蒙大拿州两个蝗虫种群的动态：天气、食物丰度和种内竞争之间的关系
作者：
G. Belovsky;J. Slade
在蒙大拿州帕卢斯草原，利用实验微观世界对两种蝗虫（Melanoplus femurrubrum 和 M. sanguinipes）的种群动态进行了长达 8 年的研究。实验群体中的蚱蜢密度、存活和繁殖以密度依赖的方式对所有蚱蜢发育阶段（无论是在所有年份内还是在年份之间）的食物供应量的自然和实验变化做出反应。我们观察到，在研究期间，现场蝗虫的野外种群表现出与实验种群相似的密度、生存和繁殖反应。因为我们无法识别野外环境和微观环境或其中的蚱蜢个体之间的任何差异，所以我们认为野外种群最终受到年份内和年份之间食物的限制。整个夏季，所有年龄段的人都出现了密度依赖的食物限制，因为食物丰度相对于整个夏季的蚱蜢食物需求量有所下降。食物限制发生在年份之间，因为在食物丰度最低的年份，种群在下一年生产的幼体数量超过了观察到的最高食物丰度所能支持的数量。最后，观察到的食物丰度的年度变化与天气（降雨量和温度）的年度变化相关，这表明蝗虫密度和天气条件之间长期建立的关系并不意味着与密度无关的过程对种群数量的限制。
The population dynamics of two grasshoppers (Melanoplus femurrubrum and M. sanguinipes) were studied using experimental microcosms over 8 years at a Palouse prairie site in Montana. Grasshopper density, survival and reproduction in the experimental populations responded in a density-dependent fashion to natural and experimental changes in food availability for all grasshopper developmental stages, both within and between all years. We observed that field populations of the grasshoppers at the site exhibited density, survival and reproductive responses similar to the experimental populations over the period of the study. Because we could not identify any differences between the field and microcosm environments or the grasshopper individuals in them, we contend that field populations were ultimately limited by food within and between years. Density-dependent food limitation occurred for all age categories over the entire summer, because food abundance declined relative to grasshopper food requirements over the summer. Food limitation occurred between years, because in years with the lowest food abundance, the populations produced more hatchlings for the next year than could be supported by the highest observed food abundance. Finally, the observed annual changes in food abundance were correlated with the annual variation in weather (rainfall and temperature), which indicated that the long established relationship between grasshopper densities and weather conditions does not imply population limitation by density-independent processes.