Ground-Vegetation Clutter Affects Phyllostomid Bat Assemblage Structure in Lowland Amazonian Forest

Vegetation clutter is a limiting factor for bats that forage near ground level, and may determine the distribution of species and guilds. However, many studies that evaluated the effects of vegetation clutter on bats have used qualitative descriptions rather than direct measurements of vegetation density. Moreover, few studies have evaluated the effect of vegetation clutter on a regional scale. Here, we evaluate the influence of the physical obstruction of vegetation on phyllostomid-bat assemblages along a 520 km transect in continuous Amazonian forest. We sampled bats using mist nets in eight localities during 80 nights (3840 net-hours) and estimated the ground-vegetation density with digital photographs. The total number of species, number of animalivorous species, total number of frugivorous species, number of understory frugivorous species, and abundance of canopy frugivorous bats were negatively associated with vegetation clutter. The bat assemblages showed a nested structure in relation to degree of clutter, with animalivorous and understory frugivorous bats distributed throughout the vegetation-clutter gradient, while canopy frugivores were restricted to sites with more open vegetation. The species distribution along the gradient of vegetation clutter was not closely associated with wing morphology, but aspect ratio and wing load differed between frugivores and animalivores. Vegetation structure plays an important role in structuring assemblages of the bats at the regional scale by increasing beta diversity between sites. Differences in foraging strategy and diet of the guilds seem to have contributed more to the spatial distribution of bats than the wing characteristics of the species alone.植被杂乱度（vegetation clutter）对近地面觅食的蝙蝠而言是一类限制因子，同时可能决定蝙蝠物种及功能群的分布格局。然而，此前多数评估植被杂乱度对蝙蝠影响的研究，多采用定性描述而非直接测量植被密度的方法。此外，鲜有研究在区域尺度上探讨植被杂乱度的影响。本研究基于亚马孙连续森林中的一条520公里样带，探究植被物理遮挡对叶口蝠科蝙蝠（Phyllostomidae）群落的影响。研究期间，我们在8个采样点布设雾网（mist nets），于80个夜间开展采样，累计采样时长达3840网时（net-hours），并通过数码照片估算地面植被密度（ground-vegetation density）。蝙蝠物种总数、食虫性物种数、食果性物种总数、林下食果性物种数，以及冠层食果蝙蝠的种群丰度，均与植被杂乱度呈负相关关系。蝙蝠群落在植被杂乱度梯度上呈现嵌套结构：食虫蝙蝠与林下食果蝙蝠分布于整个植被杂乱度梯度区间，而冠层食果蝙蝠仅局限于植被更为开阔的样点。沿植被杂乱度梯度的物种分布与翼型形态并无显著关联，但展弦比（aspect ratio）和翼载荷（wing load）在食果蝙蝠与食虫蝙蝠之间存在显著差异。在区域尺度上，植被结构通过提升样点间的β多样性（beta diversity），在蝙蝠群落构建过程中发挥重要作用。相较于物种自身的翼部特征，蝙蝠功能群的觅食策略与食性差异，对蝙蝠空间分布格局的贡献更为显著。