Testing the enemies hypothesis in forest stands:: the important role of tree species composition
Testing the enemies hypothesis in forest stands:: the important role of tree species composition
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DOI：
10.1007/s00442-004-1696-y
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发表时间：
2005-01-01
期刊：
影响因子：
2.7
通讯作者：
Vehviläinen, H
中科院分区：
文献类型：
--
作者：
Riihimäki, J;Kaitaniemi, P;Vehviläinen, H
在农业生态系统中进行的许多研究支持天敌假说，该假说指出，捕食者和寄生虫在混合栽培中比在单一栽培中更有效地控制害虫密度。然而，在森林生态系统中进行的类似研究很少，我们还没有证据表明敌人假说在森林中是否成立。在一项为期2年的研究中，我们调查了秋蛾（Epirrita autumnata）幼虫和蛹的生存是否不同的银单一和两种混合物的桦树与黑桤木，挪威云杉和苏格兰松。我们将幼虫放在桦树树苗上，监测它们的存活情况，直到幼虫期结束，然后检查它们是否被寄生。幼虫化蛹后，在田间试验中测试蛹的存活率。2002年，白桦-松树混交林中的幼虫消失较早，其总体存活率低于其他林分类型。在2003年，桦松林分的存活率仅在第一周最低，林分之间的总存活率没有差异。幼虫寄生率不受树种组成的影响。蛹的重量和蛹的生存同样不受影响的立场类型。在捕食者中，木蚁更丰富的桦树生长在桦树-松树混合比其他林分类型，可能是因为蚁蚜虫的殖民地是常见的松树。与此相反，蜘蛛的数量没有不同的立场类型。蚂蚁排除通过胶水环周围的桦树干增加幼虫的生存，表明蚂蚁是重要的捕食者的秋蛾幼虫的幼虫生存之间的差异，可能是由于差分蚂蚁捕食。我们的研究结果只提供了部分支持的敌人假说，并建议这是两个树种组成和物种多样性，影响草食动物的生存和捕食。
Numerous studies conducted in agro-ecosystems support the enemies hypothesis, which states that predators and parasites are more efficient in controlling pest densities in polycultures than in monocultures. Few similar studies, however, have been conducted in forest ecosystems, and we do not yet have evidence as to whether the enemies hypothesis holds true in forests. In a 2-year study, we investigated whether the survival of autumnal moth (Epirrita autumnata) larvae and pupae differs between silver birch monocultures and two-species mixtures of birch with black alder, Norway spruce and Scots pine. We placed young larvae on birch saplings and monitored their survival until the end of the larval period, when we checked whether they had been parasitized. After the larvae had pupated, pupal survival was tested in a field trial. In 2002, the larvae disappeared earlier and their overall survival was lower in birch - pine mixtures than in other stand types. In 2003, survival probability was lowest in birch - pine stands only during the first week and there were no differences between stands in overall survival. Larval parasitism was not affected by tree species composition. Pupal weight and pupal survival were likewise not affected by stand type. Among the predators, wood ants were more abundant on birches growing in birch - pine mixtures than in other stand types probably because colonies of myrmecophilic aphids were common on pines. In contrast, spider numbers did not differ between stand types. Ant exclusion by means of a glue ring around the birch trunk increased larval survival, indicating that ants are important predators of the autumnal moth larvae; differences in larval survival between stands are probably due to differential ant predation. Our results provide only partial support for the enemies hypothesis, and suggest that it is both tree species composition and species diversity which affect herbivore survival and predation.