Bats respond negatively to increases in the amount and homogenization of agricultural land cover

Abstract from paper: Changes in agricultural landscapes due to intensification, such as loss of natural areas, loss of grazing lands to annual row crops, and increased use of pesticides, have led to widespread declines in biodiversity. Bats are expected to respond negatively to agricultural intensification because of reductions in prey abundance and roosting habitat availability. We measured relative bat abundance with acoustic bat recorders in landscapes that varied in (1) the proportion of agriculture and (2) the proportion of agriculture that is in annual row crops vs. perennial forages (pasture and hay). We predicted that relative bat abundance would be highest where (1) the proportion of agriculture was low and (2) the agriculture was dominated by perennial forage. Consistent with our first prediction, the abundance or presence of four bat species, total bat abundance and bat species richness declined with increasing agricultural cover. Counter to our second prediction, we did not find a negative relationship between species richness or relative bat abundance or presence and the proportion of agricultural land that is in annual row crops. Instead we found that the abundance of three bat species, total bat abundance and bat species richness were greatest where the proportion of agriculture in annual crops was about equal to the proportion in perennial forage. Based on these results, we suggest that bat abundance and richness can be increased in agricultural landscapes by reducing the conversion of natural areas to agriculture and by maintaining a balance of perennial forage and annual crop agricultural cover types.

论文摘要：农业集约化进程引发的农田景观变化，包括自然区域丧失、放牧地被一年生大田作物（annual row crops）替代，以及农药使用量增加，已导致生物多样性出现大范围下降。由于猎物丰度下降与栖息生境可获得性降低，蝙蝠被认为会对农业集约化产生负面响应。我们借助声学蝙蝠记录仪（acoustic bat recorders），在两类景观梯度中测定蝙蝠相对丰度：一是农业用地占比，二是农业用地中一年生大田作物与多年生饲草（perennial forages，含牧场与干草）的占比结构。我们提出两项预测：其一，农业用地占比越低，蝙蝠相对丰度越高；其二，农业用地以多年生饲草为主时，蝙蝠相对丰度更高。研究结果与第一项预测相符：4个蝙蝠物种的丰度或出现频次、蝙蝠总丰度以及蝙蝠物种丰富度，均随农业用地占比提升而下降。但研究结果与第二项预测相悖：我们未发现蝙蝠物种丰富度、相对丰度或出现频次，与农业用地中一年生大田作物占比之间存在负相关关系。相反，我们发现3个蝙蝠物种的丰度、蝙蝠总丰度以及物种丰富度，在一年生作物占比与多年生饲草占比大致相当的区域达到最高水平。基于上述结果，我们建议：通过减少自然区域向农业用地的转化，以及维持多年生饲草与一年生作物两类农业覆盖类型的占比平衡，可提升农田景观中的蝙蝠丰度与物种丰富度。