Abstract
Land‐use and management are disturbance factors that have diverse effects on community composition and structure. In traditional rural grasslands, such as meadows and pastures, low‐intensity management is maintained to enhance biodiversity. Maintenance of road verges, in turn, creates habitat, which may complement traditional rural grasslands. To evaluate the effect of low‐intensity disturbance on insect communities, we characterized species abundance distributions (SAD) for Carabidae, Formicidae, and Heteroptera in three grassland types, which differed in management: meadows, pastures, and road verges. The shape of SAD was estimated with three parameters: abundance decay rate, dominance, and rarity. We compared the SAD shape among the grassland types and tested the effect of environmental heterogeneity (plant species richness) and disturbance intensity (trampling in pastures) on SADs. The shape of SADs did not differ among the grassland types but among the taxonomic groups instead. Abundance decay rate and dominance were larger for Formicidae, and rarity smaller, than for Carabidae and Heteroptera. For Carabidae and window‐trapped Heteroptera, rarity increased with increasing plant species richness. For Formicidae, dominance increased with trampling intensity in pastures. Although the SAD shape remained largely unchanged, the identity of the dominant species tended to vary within and among grassland types. Our study shows that for a given taxonomic group, the SAD shape is similar across habitat types with low‐intensity disturbances resulting from different management. This suggests that SADs respond primarily to the intensity of disturbance and thus could be best used in monitoring communities across strong disturbance and environmental gradients. Because taxonomic groups can inherently have different SADs, taxon‐specific SADs for undisturbed communities must be empirically documented before the SAD shape can be used as an indicator of environmental change. Because the identity of the dominant species changes from management type to another, the SAD shape alone is not an adequate monitoring tool.
Highlights
Grasslands are species rich but threatened habitats globally (Hoekstra et al 2005)
We characterized the empirical species abundance distributions (SAD) for insect communities (Carabidae, Formicidae, and Heteroptera) in three grassland types, which differed in their management
We further studied whether the SAD shape changes along with environmental heterogeneity and disturbance, and whether these changes are consistent among different taxa and grassland types
Summary
Grasslands are species rich but threatened habitats globally (Hoekstra et al 2005). Especially, meadows and pastures, which traditionally were maintained by low-intensity haymaking and grazing, have become rare (Tscharntke et al 2005). There has been a recent change in the research outlook; rather than testing a plethora of statistical models and searching for the best fit, the alternative approach to analyze how different SAD properties (e.g., skewness) vary with different predictor variables has gained popularity (Matthews & Whittaker 2014; Simons et al 2015) This has better allowed for quantitative comparison of community changes across habitat types, land-use intensities, or disturbance gradients (Dornelas et al 2009; Yen et al 2013; Simons et al 2015), and the use of SADs in applied ecology has increased (Matthews & Whittaker 2015). Given the differences in the ecology of the studied taxa, we expect that the identity of the dominant species should vary among the grassland types, and some of the changes in the SAD shape should be taxon-specific
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