Abstract
Recently reported insect declines have raised both political and social concern. Although the declines have been attributed to land use and climate change, supporting evidence suffers from low taxonomic resolution, short time series, a focus on local scales, and the collinearity of the identified drivers. In this study, we conducted a systematic assessment of insect populations in southern Germany, which showed that differences in insect biomass and richness are highly context dependent. We found the largest difference in biomass between semi-natural and urban environments (−42%), whereas differences in total richness (−29%) and the richness of threatened species (−56%) were largest from semi-natural to agricultural environments. These results point to urbanization and agriculture as major drivers of decline. We also found that richness and biomass increase monotonously with increasing temperature, independent of habitat. The contrasting patterns of insect biomass and richness question the use of these indicators as mutual surrogates. Our study provides support for the implementation of more comprehensive measures aimed at habitat restoration in order to halt insect declines.
Highlights
Reported insect declines have raised both political and social concern
With agricultural intensification considered as a major driver of insect decline[9], new laws and strategies have been implemented in many countries in order to provide additional resources for farmland species, improve the quality of landscape habitats, and reduce pesticide use in agricultural production[10]
By combining Malaise traps and DNA-metabarcoding, our work is not limited to single factors such as biomass measurements or assessment of single taxa to reveal drivers of insect communities
Summary
Reported insect declines have raised both political and social concern. the declines have been attributed to land use and climate change, supporting evidence suffers from low taxonomic resolution, short time series, a focus on local scales, and the collinearity of the identified drivers. With agricultural intensification considered as a major driver of insect decline[9], new laws and strategies have been implemented in many countries in order to provide additional resources for farmland species, improve the quality of landscape habitats, and reduce pesticide use in agricultural production[10]. Meta-analyses of time series have been hindered by the fact that existing research has primarily focused on only a few taxa[18] or on certain facets of biodiversity, such as biomass or species richness[9,19], these parameters may respond differently to different drivers of global change[9,20,21] and may be influenced by the spatial scale considered. Space-for-time studies allow the inclusion of a large number of sampling locations and assessments of the combined impacts of climate and land-use intensity across all land-use types, from semi-natural to agricultural to urban
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