Losers and winners: responses of grassland arthropods to land-use components

Anthropogenic pressures such as land-use intensification in grasslands increasingly threaten biodiversity by altering habitat structure. Particularly arthropods show highly variable responses to these pressures depending on the species, its traits and its habitat requirements.

For this study, we used quantitative niche models (a randomization method based on a null model) to assess species-specific responses and their abundance-weighted means (AWM) of the arthropods to mowing, fertilizing, and grazing. Species with observed AWM lower than 95% of the AWM_null values (p < 0.05) were treated as ‘loser', while those with AWM higher than 95% of the AWM_null values (p < 0.05) were identified as ‘winner'. We therefore analysed 1,352 arthropod species of four arthropod orders (Araneae, Coleoptera, Hemiptera, Orthoptera) across three regions in Germany (150 grassland plots) between 2008 and 2018.

The results reveal three times as many species were categorized as losers compared to winners and that fertilizing had the most detrimental effects, since fertilizing produced the fewest winners and the most losers. Grazing, however, yielded the highest proportion of winners and the fewest losers. Yet, neutral species still predominate as most species are generalists to human pressure and results may vary depending on the traits a specific species possesses. For example, grazing favored smaller species, whereas mowing and fertilizing favored larger ones, and herbivores were particularly sensitive to fertilizing. A further comparison of the results with the protection and conservation status of the German Red List showed that intensive management practices affect the already most vulnerable species. Especially, species negatively affected by mowing were overrepresented in higher-risk Red List categories, as well reflected by declining population trends.

This study demonstrates that arthropod responses to land-use are highly heterogeneous, but underline niche modeling as a robust tool for analyzing species-specific responses to land-use and management practices, which can be used as a basis with the Red List to develop targeted conservation strategies tailored to the ecological requirements of vulnerable species.