Landscape heterogeneity rather than crop diversity mediates bird diversity in agricultural landscapes

Abstract

Crop diversification has been proposed as farm management tool that could mitigate the externalities of conventional farming while reducing productivity-biodiversity trade-offs. Yet evidence for the acclaimed biodiversity benefits of landscape-level crop diversity is ambiguous. Effects may strongly depend on spatial scale and the level of landscape heterogeneity (e.g. overall habitat diversity). At the same time, contrasting within-taxon responses obscure benefits to specific functional groups (i.e. species with shared characteristics or requirements) if studied at the community level. The objectives of this study were to 1) disentangle the relative effects of crop diversity and landscape heterogeneity on avian species richness across five spatial scales ranging from 250 to 3000 m radii around focal winter wheat fields; and 2) assess whether functional groups (feeding guild, conservation status, habitat preference, nesting behaviour) determine the strength and direction of responses to crop diversity and landscape heterogeneity. In central Germany, 14 landscapes were selected along independent gradients of crop diversity (annual arable crops) and landscape heterogeneity. Bird species richness in each landscape was estimated using four point counts throughout the breeding season. We found no effects of landscape-level crop diversity on bird richness and functional groups. Instead, landscape heterogeneity was strongly associated with increased total bird richness across all spatial scales. In particular, insect-feeding and non-farmland birds were favoured in heterogeneous landscapes, as were species not classified as endangered or vulnerable on the regional Red List. Crop-nesting farmland birds, however, were less species-rich in these landscapes. Accordingly, crop diversification may be less suitable for conserving avian diversity and associated ecosystem services (e.g. biological pest control), although confounding interactions with management intensity need yet to be confirmed. In contrast, enhancement of landscape heterogeneity by increasing perennial habitat diversity, reducing field sizes and the amount of cropland has the potential to benefit overall bird richness. Specialist farmland birds, however, may require more targeted management approaches.

Impact of Energy Landscapes on the Abundance of Eurasian Skylark (Alauda arvensis), an Example from North Germany

“…We found a negative significant correlation between SDI and ESA. Our results confirm that, at the regional (CLC) scale, the increasing landscape heterogeneity has a negative effect on the population of the Eurasian skylark [19,21,37,40,41]. The increasing heterogeneity results in a lower abundance of the Eurasian skylark.…”

“…According to Chamberlain et al (2001) [45], in England, the skylark density increased with habitat heterogeneity; nevertheless, farmland plots in the lowlands of England showed decreased skylark density with increasing habitat heterogeneity. These results suggest that the crop type is more important than the crop heterogeneity value [41]. According to Blaschke et al [46], an increase in cultivation of bioenergy crops inside the biogas energy landscape will decrease the land availability for traditional agriculture and nature conservation.…”

Landscape structure influences the use of social information in an insectivorous bat

“…Agricultural landscapes characterised by large fields and few ecotones possess low compositional and configurational habitat complexity (Robinson and Sutherland ). In such simplified landscapes, abundance and diversity of animals is often reduced (Fahrig et al , Newbold et al , Redlich et al ). A potential underlying mechanism might be that on the landscape scale resource heterogeneity increases with decreasing habitat complexity, making it more difficult for consumers to find food resources (Mueller and Fagan ).…”

Laboratory and field tests of predation on the cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae)

“…Using data from 31 countries, Karp et al (2018) reported inconsistent associations between pest control and semi-natural habitats in the surrounding landscapes, suggesting that the semi-natural habitats in the agricultural landscape do not always enhance biological control of herbivores. Furthermore, some crops, including alfalfa (Costamagna et al, 2015) and wheat (Samaranayake & Costamagna, 2018), and crop diversity (Redlich et al, 2018) have been associated with increased pest control services, suggesting that crop habitats may also function as temporary sources of natural enemies .…”