Landscape diversity and local temperature, but not climate, affect arthropod predation among habitat types

Arthropod predators are relevant for top-down regulation of insect herbivores. Biotic and abiotic factors influence predator communities and their activity with consequences for the strength of top-down regulation (‘arthropod predation’). Anthropogenic climate and land-use change urges a deeper understanding of the combined effects of potential drivers on arthropod predation. This study obtained arthropod predation rates on 113 plots of open herbaceous vegetation adjacent to different habitat types (forest, grassland, arable field, settlement) along climate and land-use gradients in Bavaria, Germany, using a standardized method of artificial caterpillars at ground level. Predation rates were analysed with regard to habitat characteristics (habitat type, plant species richness, local mean temperature and mean relative humidity during artificial caterpillar exposure), landscape diversity (0.5–3.0-km, six scales), climate (multi-annual mean temperature, ‘MAT’) and interactive effects of habitat type with other drivers. Arthropod predation rates did not substantially differ between the studied habitat types, related to plant species richness and across the Bavarian-wide climatic temperature gradient, and also no interactive effects were observed. However, arthropod predation rates were limited by low local mean temperatures, tended to decrease towards higher relative humidity and increased towards more diverse landscapes at a 2-km scale. Thus, high arthropod predation rates in open herbaceous vegetation are favoured by diverse landscapes independent of the dominant habitat in the vicinity. Diversifying landscapes may help to improve top-down control of herbivores, e.g. agricultural pests, but more research is needed to derive specific recommendations on landscape management. Little influence of MAT on predation rates suggests that moderate increases of MAT may not strongly alter this process in the near future.

Methods
Twenty artificial caterpillars made from green plasticine (diameter 3 mm, length 20 mm) were placed at ground level on open herbaceous vegetation for a 2-d period. Arthropod attack marks on caterpillars were assessed in the field, and those caterpillars brought to the lab were double-checked (raw data). From the number of assessed caterpillars with and without arthropod attack marks, arthropod predation rates were calculated and data aquired in deviation from the protocol were excluded (processed data). For details see 'Fricke et al predation data processing' in the usage notes and address the related manuscript.