Spatiotemporal variation of Diptera changes how we evaluate High Nature Value (HNV) wet grasslands

Proposed strategies to protect biodiversity within agricultural systems are often based on botanical criteria with plant species richness generally considered the prime indicator of conservation potential. While wet grasslands dominated by rushes (Juncus spp.) are commonly considered to be of lesser ecological value than those which are more botanically diverse (e.g. Carex dominated wet grasslands), their value for invertebrates such as Diptera has not yet been fully explored. Data from two Diptera families (Sciomyzidae and Syrphidae) were examined at spatial, temporal and spatiotemporal scales to determine the contribution of two different (Juncus and Carex dominated) wet grassland habitats towards the maintenance of Diptera diversity. The two habitats were significantly different in terms of community structure for both families and temporal variation was a significant component of dipteran diversity. Spatiotemporal analysis showed that species turnover between habitats at different times made the most significant contribution to overall Diptera diversity. Temporal variation of both families suggests that the relative importance of each habitat type to overall diversity fluctuates depending on sampling period, with both habitats supporting diversity at different times. Our results indicate that lowland wet grasslands characterised by Juncus cover need to be recognised as ecologically important for the maintenance of dipteran diversity. We discuss the possible implications for the diversity of Diptera in wet grasslands if these commonly perceived marginal areas (both agriculturally and ecologically) are ignored in conservation strategies. The necessity of recognising spatiotemporal variation when evaluating habitats using invertebrates as indicators is also discussed. © 2017 Springer Science+Business Media Dordrech

Indicators of Diptera diversity in wet grassland habitats are influenced by environmental variability, scale of observation, and habitat type

In low intensity agri-ecosystems such as wet grassland habitats, the inclusion of invertebrates in conservation assessments and monitoring is usually limited to charismatic groups such as bees or butterflies. However, wet grasslands support a wide range of inveterate groups, some of which may exhibit limited movement not generally represented by more mobile groups such as those typically examined. The use of surrogate species which exemplify broader invertebrate diversity has been suggested as a possible means of including these overlooked invertebrates (such as Diptera) in conservation planning within these habitats. Based on collections made by Malaise trap, we utilized two families of Diptera (Sciomyzidae and Syrphidae) as indicators of a wider range of dipteran diversity (nine Diptera families identified to parataxonomic unit level [PUs]) in wet grassland habitats. We examined the role of environmental variability, spatial scale, and habitat type on patterns of cross-taxon congruence for all three assemblages. Both environmental correlation and community congruence were significantly stronger among assemblages when examined at low spatial scales, highlighting the need to examine dipteran groups at scales untypical of current agri-environmental assessments; namely field and farm level. Furthermore, when wet grasslands were differentiated into two habitat categories (sedge and rush dominated grasslands), the significance of the community congruence increased markedly. This correlation was particularly strong between Sciomyzidae and PUs which demonstrated similar differentiation based on habitat type, implying that assemblages which exhibit comparable ecological partitioning are more likely to be useful surrogates of one another. Correlations between richness, abundance and Shannon's diversity were highly variable among groups, suggesting compositional analysis as the most appropriate examination of dipteran diversity for surrogacy studies. The results indicate that cross-assemblage congruence of Diptera is influenced by similarity of response to environmental variability, scale of observation, and examination of assemblages differentiated into appropriate habitat categories. The results illustrate the need to investigate invertebrate biodiversity surrogates at scales appropriate to the indicator groups and examine congruence among assemblages within specific habitat categories. Such an approach has the potential to maximise gamma diversity in areas where wet grasslands are under threat of intensification or abandonment. © 2017 Elsevier Lt