Arthropod niche differentiation linked to grazing‐induced sward islets in intensively managed agricultural pasture

Abstract The distribution of Araneae, Coleoptera, Hemiptera and Hymenoptera relative to sward islets was investigated using suction sampling in improved grass pastures on 26 farms and in a pasture management experiment in Ireland. Species accumulation curves indicated significant differences between islet and non‐islet sub‐habitats in the number of taxa plotted against sample, but not when plotted against individuals, indicating no difference in overall species richness. Non‐metric multidimensional scaling (NMDS) ordination of islet and non‐islet communities indicated marked differences in arthropod community composition. Modelling abundance of specific taxa with islet and sward height data allowed arthropod taxa to be categorised as (i) islet‐positive, (ii) islet‐negative, (iii) taxa showing mixed responses and (iv) taxa showing no significant effects. Most taxa were found to be more abundant within islets. In some instances, this may be best explained by a more generalised response to sward height. Some taxa clearly showed a specifically positive islet effect with no significant response to sward height per se. A minority of taxa clearly occurred more frequently outside islet patches, and few abundant taxa were found to be indifferent to the presence of islets. Differences in distribution relative to islets indicated niche differentiation, most likely based on characteristics of the islets, such as micro‐climate, and nutritional or shelter requirements. Spatial responses to islets clearly generate additional variation within arthropod communities, which contributes to the maintenance of biodiversity within grazed agricultural grasslands.