Impact of food and predation on the snowshoe hare cycle

Snowshoe hare populations in the boreal forests of North America go through 10-year cycles. Supplemental food and mammalian predator abundance were manipulated in a factorial design on 1-square-kilometer areas for 8 years in the Yukon. Two blocks of forest were fertilized to test for nutrient effects. Predator exclosure doubled and food addition tripled hare density during the cyclic peak and decline. Predator exclosure combined with food addition increased density 11-fold. Added nutrients increased plant growth but not hare density. Food and predation together had a more than additive effect, which suggests that a three-trophic-level interaction generates hare cycles.     

EPG技术分析不同品种茶树抗假眼小绿叶蝉取食行为的差异

假眼小绿叶蝉是我国最严重的茶树害虫,不同品种对其表现出抗性或感性,EPG是近年用于快速检测作物抗刺吸式害虫的新技术。以浙江、江苏主推的6个茶树良种为供试材料,用可视的DC-EPG技术记录了该叶蝉的刺探取食行为。结果表明:(1)叶蝉在6个品种茶树上的7种基本刺吸波形是相同的。(2)在锡茶5号、苏茶1号上的刺探次数多,在韧皮部内的被动取食波-E波的持续时间长;在龙井43上刺探次数少,在韧皮部内的被动取食波E波持续时间短;苏茶120、中茶108和安吉白茶则居中。(3)使用聚类分析、多重比较分析,评判6个品种茶树抗叶蝉取食能力由强至弱的顺序为龙井43>苏茶120>中茶108>安吉白茶>苏茶1号>锡茶5号,该顺序与田间观察的6个品种茶树上叶蝉虫口密度由小到大的顺序基本一致。认为EPG技术可用于评判不同品种茶树对叶蝉抗性的强弱。