Spatial distribution of soil insects in grassland
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Recently, there has been interest in the study of soil biodiversity and its functional role in agricultural grassland due to the need to develop management strategies for soil biota to improve ecosystem self-regulation. In the UK, grasslands provide a habitat for several subterranean insect taxa some of which are pests - leatherjackets (larvae of Tipulidae: Diptera) and wireworms (larvae of Elateridae:Coleoptera). To provide an appropriate method of pest management, a systematic sampling of agricultural grassland over different sampling scales is crucial in order to understand their population distribution and distribution patterns. The spatial distribution and distribution patterns of soil insects were investigated in agricultural grassland over three sampling scales (farmlet, field and core). The effect of spatial, biotic and scale variables and their combinations have been assessed. In addition, a new molecular method has been developed to identify grassland leatherjackets using universal DNA primers. Soil core samples were collected from 19 grass fields divided into 3 farmlets in the Farm Platform at Rothamsted Research, North Wyke. The abundance of taxa and presence: absence data were analysed over the three sampling scales using variance/mean ratios, non-metric multidimensional scaling to visualise association between individual taxa, and deviance partitioning to determine the effect of spatial, space and biotic variables on species distribution. The spatial distribution of most taxa varied between sampling scales from randomness at the core scale to aggregation at the field and farm scales, though some taxa were aggregated at nearly all scales. Using deviance partitioning our results support previous reports and suggest that scale is the most important factor influencing taxa distribution in comparison with biotic and space variables which had a minor impact. This could explain the variation between taxa which might be due to the interactions between specific environmental variables and sampling scale, biotic and other unknown factors and species biology. DNA barcoding of Tipula spp. using universal DNA primers showed that leatherjackets in grassland are dominated by Tipula paludosa with T. oleraca only found in small numbers. There were also some species of T. paludosa with high genetic variability (P>3%) within the species indicating the possibility of other cryptic species close to T. paludosa.
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