Muiruri Evalyne W, Rainio Kalle, Koricheva Julia
School of Biological Sciences, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK.
Department of Biology, University of Turku, 20014, Turku, Finland.
Oecologia. 2016 Mar;180(3):619-30. doi: 10.1007/s00442-015-3391-6. Epub 2015 Jul 23.
The enemies hypothesis states that reduced insect herbivory in mixed-species stands can be attributed to more effective top-down control by predators with increasing plant diversity. Although evidence for this mechanism exists for invertebrate predators, studies on avian predation are comparatively rare and have not explicitly tested the effects of diversity at different spatial scales, even though heterogeneity at macro- and micro-scales can influence bird foraging selection. We studied bird predation in an established forest diversity experiment in SW Finland, using artificial larvae installed on birch, alder and pine trees. Effects of tree species diversity and densities on bird predation were tested at two different scales: between plots and within the neighbourhood around focal trees. At the neighbourhood scale, birds preferentially foraged on focal trees surrounded by a higher diversity of neighbours. However, predation rates did not increase with tree species richness at the plot level and were instead negatively affected by tree height variation within the plot. The highest probability of predation was observed on pine, and rates of predation increased with the density of pine regardless of scale. Strong tree species preferences observed may be due to a combination of innate bird species preferences and opportunistic foraging on profitable-looking artificial prey. This study therefore finds partial support for the enemies hypothesis and highlights the importance of spatial scale and focal tree species in modifying trophic interactions between avian predators and insect herbivores in forest ecosystems.
“天敌假说”认为，在混交林中昆虫食草行为减少可归因于随着植物多样性增加，捕食者自上而下的控制作用更有效。尽管有证据表明这种机制适用于无脊椎动物捕食者，但关于鸟类捕食的研究相对较少，而且即使宏观和微观尺度的异质性会影响鸟类的觅食选择，也尚未明确测试不同空间尺度下多样性的影响。我们在芬兰西南部一个已开展的森林多样性实验中研究鸟类捕食情况，将人工幼虫放置在桦树、桤木和松树上。在两个不同尺度上测试了树种多样性和密度对鸟类捕食的影响：样地之间以及焦点树周围的邻域内。在邻域尺度上，鸟类优先在被更多样化的邻居包围的焦点树上觅食。然而，在样地水平上，捕食率并未随着树种丰富度的增加而提高，反而受到样地内树高变化的负面影响。在松树上观察到的被捕食概率最高，且无论在哪个尺度上，捕食率都随着松树密度的增加而上升。观察到的强烈树种偏好可能是由于鸟类天生的物种偏好以及对看似有利可图的人工猎物的机会主义觅食行为共同作用的结果。因此，本研究为“天敌假说”提供了部分支持，并强调了空间尺度和焦点树种在改变森林生态系统中鸟类捕食者与昆虫食草动物之间营养相互作用方面的重要性。
