Institute of Experimental Ecology, University of Ulm, Ulm, Germany.
PLoS One. 2011 Apr 4;6(4):e17857. doi: 10.1371/journal.pone.0017857.
The intensive foraging of insectivorous birds and bats is well known to reduce the density of arboreal herbivorous arthropods but quantification of collateral leaf damage remains limited for temperate forest canopies. We conducted exclusion experiments with nets in the crowns of young and mature oaks, Quercus robur, in south and central Germany to investigate the extent to which aerial vertebrates reduce herbivory through predation. We repeatedly estimated leaf damage throughout the vegetation period. Exclusion of birds and bats led to a distinct increase in arthropod herbivory, emphasizing the prominent role of vertebrate predators in controlling arthropods. Leaf damage (e.g., number of holes) differed strongly between sites and was 59% higher in south Germany, where species richness of vertebrate predators and relative oak density were lower compared with our other study site in central Germany. The effects of bird and bat exclusion on herbivory were 19% greater on young than on mature trees in south Germany. Our results support previous studies that have demonstrated clear effects of insectivorous vertebrates on leaf damage through the control of herbivorous arthropods. Moreover, our comparative approach on quantification of leaf damage highlights the importance of local attributes such as tree age, forest composition and species richness of vertebrate predators for control of arthropod herbivory.
食虫鸟类和蝙蝠的密集觅食行为众所周知会降低树木食草节肢动物的密度，但对于温带森林树冠，对附带的叶片损伤的量化仍然有限。我们在德国南部和中部的年轻和成熟的橡树树冠中进行了带有网的排除实验，以研究空中脊椎动物通过捕食减少食草作用的程度。我们在整个植被期内反复估计叶片损伤。鸟类和蝙蝠的排除导致明显增加了节肢动物的食草性，强调了脊椎动物捕食者在控制节肢动物方面的突出作用。叶片损伤（例如，孔数）在不同地点之间差异很大，德国南部的叶片损伤比我们在德国中部的其他研究地点高出 59%，这是因为德国南部的脊椎动物捕食者的物种丰富度和相对橡树密度较低。在德国南部，鸟类和蝙蝠排除对食草性的影响在年轻树上比在成熟树上大 19%。我们的结果支持了先前的研究，这些研究表明食虫脊椎动物通过控制食草节肢动物对叶片损伤有明显的影响。此外，我们对叶片损伤进行量化的比较方法强调了当地属性（如树木年龄、森林组成和脊椎动物捕食者的物种丰富度）对控制节肢动物食草性的重要性。
