Strong declines of grassland species diversity in small and isolated grassland patches have been observed at local and landscape scales. Here, we study how plant–herbivore interaction webs and habitat specialisation of leafhopper communities change with the size of calcareous grassland fragments and landscape connectivity. We surveyed leafhoppers and plants on 14 small (0.1–0.6 ha) and 14 large (1.2–8.8 ha) semi-natural calcareous grassland fragments in Central Germany, differing in isolation from other calcareous grasslands and in the percentage of arable land in the surrounding landscape (from simple to complex landscapes). We quantified weighted trophic links between plants and their phytophagous leafhoppers for each grassland fragment. We found that large and well-connected grassland fragments harboured a high portion of specialist leafhopper species, which in turn yielded low interaction diversity and simple plant-leafhopper food webs. In contrast, small and well-connected fragments exhibited high levels of generalism, leading to higher interaction diversity. In conclusion, food web complexity appeared to be a poor indicator for the management of insect diversity, as it is driven by specialist species, which require high connectivity of large fragments in complex landscapes. We conclude that habitat specialists should be prioritized since generalist species associated with small fragments are also widespread in the surrounding landscape matrix.

在局部和景观尺度上观察到小而孤立的草地斑块中草地物种多样性的强烈下降。在这里，我们研究了叶蝉群落的植物-草食动物相互作用网络和栖息地专业化如何随着钙质草原碎片的大小和景观连通性而变化。我们在德国中部的 14 个小型（0.1-0.6 公顷）和 14 个大型（1.2-8.8 公顷）半天然钙质草地碎片上调查了叶蝉和植物，这些草地与其他钙质草地的隔离度和周围可耕地的百分比不同景观（从简单到复杂的景观）。我们量化了每个草原碎片的植物与其植食性叶蝉之间的加权营养联系。我们发现大型且连接良好的草原碎片含有大量专业叶蝉物种，这反过来又产生了低相互作用多样性和简单的植物叶蝉食物网。相比之下，小且连接良好的片段表现出高度的普遍性，从而导致更高的交互多样性。总之，食物网复杂性似乎不是昆虫多样性管理的一个糟糕指标，因为它是由专业物种驱动的，这需要复杂景观中大片段的高度连通性。我们得出结论，应优先考虑栖息地专家，因为与小碎片相关的通才物种在周围的景观矩阵中也很普遍。小且连接良好的片段表现出高度的普遍性，从而导致更高的交互多样性。总之，食物网复杂性似乎不是昆虫多样性管理的一个糟糕指标，因为它是由专业物种驱动的，这需要复杂景观中大片段的高度连通性。我们得出结论，应优先考虑栖息地专家，因为与小碎片相关的通才物种在周围的景观矩阵中也很普遍。小且连接良好的片段表现出高度的普遍性，从而导致更高的交互多样性。总之，食物网复杂性似乎不是昆虫多样性管理的一个糟糕指标，因为它是由专业物种驱动的，这需要复杂景观中大片段的高度连通性。我们得出结论，应优先考虑栖息地专家，因为与小碎片相关的通才物种在周围的景观矩阵中也很普遍。