Nitrogen (N) deposition from agriculture and combustion of fossil fuels is a major threat to plant diversity, but its effects on organisms at higher trophic levels are unclear. We investigated how N deposition may affect species richness and abundance (number of individuals per species) in butterflies. We reviewed the peer-reviewed literature on variables used to explain spatial variation in butterfly species richness and found that vegetation variables appeared to be as important as climate and habitat variables in explaining butterfly species richness. It thus seemed likely that increased N deposition could indirectly affect butterfly communities via its influence on plant communities. To test this prediction, we analyzed data from the Swiss biodiversity monitoring program for vascular plants and butterflies in 383 study sites of 1 km² that are evenly distributed throughout Switzerland. The area has a modeled N deposition gradient of 2–44 kg N ha⁻¹ year⁻¹. We used traditional linear models and structural equation models to infer the drivers of the spatial variation in butterfly species richness across Switzerland. High N deposition was consistently linked to low butterfly diversity, suggesting a net loss of butterfly diversity through increased N deposition. We hypothesize that at low elevations, N deposition may contribute to a reduction in butterfly species richness via microclimatic cooling due to increased plant biomass. At higher elevations, negative effects of N deposition on butterfly species richness may also be mediated by reduced plant species richness. In most butterfly species, abundance was negatively related to N deposition, but the strongest negative effects were found for species of conservation concern. We conclude that in addition to factors such as intensified agriculture, habitat fragmentation, and climate change, N deposition is likely to play a key role in negatively affecting butterfly diversity and abundance.

中文翻译：

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氮沉降对瑞士蝴蝶的负面影响

来自农业和化石燃料燃烧的氮 (N) 沉积是对植物多样性的主要威胁，但其对更高营养水平的生物体的影响尚不清楚。我们研究了 N 沉积如何影响蝴蝶的物种丰富度和丰度（每个物种的个体数量）。我们回顾了用于解释蝴蝶物种丰富度空间变化的变量的同行评审文献，发现植被变量在解释蝴蝶物种丰富度方面似乎与气候和栖息地变量一样重要。因此，增加的氮沉积似乎可能通过对植物群落的影响间接影响蝴蝶群落。为了验证这一预测，我们分析了瑞士生物多样性监测计划对 1 公里范围内 383 个研究地点的维管植物和蝴蝶的数据²均匀分布在整个瑞士。该地区的模拟氮沉降梯度为 2–44 kg N ha ^-1年^-1. 我们使用传统的线性模型和结构方程模型来推断瑞士蝴蝶物种丰富度空间变化的驱动因素。高氮沉积始终与低蝴蝶多样性相关，表明通过增加氮沉积会净损失蝴蝶多样性。我们假设在低海拔地区，由于植物生物量的增加，N 沉积可能通过微气候冷却导致蝴蝶物种丰富度的减少。在较高海拔地区，氮沉降对蝴蝶物种丰富度的负面影响也可能通过植物物种丰富度的降低来调节。在大多数蝴蝶物种中，丰度与 N 沉降呈负相关，但对受保护物种的负面影响最强。我们得出结论，除了集约化农业等因素外，