Assessing the importance of field margins for bat species and communities in intensive agricultural landscapes - Data

Landscape simplification and degradation through agricultural intensification is widely recognized as a main driver of biodiversity loss. In intensively used agricultural landscapes, patches of semi-natural habitats and particularly connections between them are of high importance for many taxa. Vegetated connections like hedgerows are especially important for foraging and commuting of mobile taxa such as bats. However, the interest of another treeless linear habitat – herbaceous field margins – remains unstudied for insectivorous bats. Field margins are nevertheless known as an important habitat for other taxa, including bat prey. Here we assessed the importance of field margins for bats compared to other landscape variables. We measured bat activity based on a repeated passive acoustic monitoring during 17 complete nights in summer on 112 study sites in an intensively used agricultural landscape. Each night, we sampled bat species activity and community metrics (i.e. species richness and community habitat specialization index) at different distances to field margins, and along a gradient of relative density of field margins. To compare field margin effects with other landscape variables, the sampled sites were selected by keeping a large variability in these other variables (land-cover Shannon diversity index, forests, hedgerows, water bodies, main roads, urban areas, grasslands, number of crops and rapeseed percentage). Only Myotis sp. were affected by herbaceous field margins. Specifically, the Myotis group activity decreased with the distance to herbaceous field margins (i.e. towards field crop cores), and positively correlated with relative density of herbaceous field margins, for which the effect size was comparable to other landscape variables. However, other landscape variables such as the proportion of and the distance to forests, the relative density of and the distance to hedgerows or land-cover Shannon diversity index, affected species richness, community specialization index, and bat activity of species from open, edge and narrow-space foragers, including the Myotis group as well. Our results highlight that herbaceous field margins have a positive effect on the activity of narrow-space bat foragers as Myotis species, but do not replace other landscape variables that drive the activity of the whole community.农业集约化引发的景观简化与退化，已被广泛认定为生物多样性丧失的主要驱动因素之一。在集约化利用的农业景观中，半自然生境斑块，尤其是斑块之间的连通性，对多数生物类群具有极高的生态重要性。诸如树篱（hedgerows）这类植被连通生境，对蝙蝠等移动性生物类群的觅食与往返通勤行为尤为关键。然而，目前学界对食虫蝙蝠与这一无树线性生境——草本农田边缘（herbaceous field margins）——的相关研究仍存在空白。尽管如此，农田边缘已被证实是包括蝙蝠猎物在内的诸多生物类群的重要栖息生境。 本研究对比其他景观变量，评估了草本农田边缘对蝙蝠的生态重要性。 我们于夏季的17个完整夜间，在某集约化农业景观内的112个研究样地中开展重复被动声学监测（passive acoustic monitoring），以此量化蝙蝠活动水平。每晚，我们在距草本农田边缘的不同距离处，以及沿草本农田边缘相对密度梯度的样点中，采集蝙蝠物种活动数据与群落指标，包括物种丰富度（species richness）及群落生境特化指数（community habitat specialization index）。 为对比草本农田边缘与其他景观变量的效应，我们在选取样地时尽可能保留了其他变量的大范围变异性，这些变量涵盖：土地覆盖香农多样性指数（Shannon diversity index）、森林、树篱、水体、主干道、城镇区域、草地、作物数量及油菜占比。 仅鼠耳蝠属（Myotis sp.）的活动受到草本农田边缘的影响。具体而言，鼠耳蝠类群的活动水平随距草本农田边缘的距离增加（即向农田核心区域延伸）而降低，且与草本农田边缘的相对密度呈正相关；该生境的效应量与其他景观变量相当。 不过，其他景观变量——如森林占比与距森林的距离、树篱的相对密度与距树篱的距离，抑或土地覆盖香农多样性指数——则会影响开阔生境、边缘生境及窄空间觅食者的物种丰富度、群落特化指数及蝙蝠活动，其中也包括鼠耳蝠类群。 本研究结果表明，草本农田边缘对鼠耳蝠这类窄空间觅食蝙蝠的活动具有积极作用，但无法替代驱动整个蝙蝠群落活动的其他景观变量。