Landscape configuration, organic management, and within‐field position drive functional diversity of spiders and carabids

Abstract

1. Agricultural management intensity and landscape heterogeneity act as the main drivers of biodiversity loss in agricultural landscapes while also determining ecosystem services. The trait-based functional diversity approach offers a way to assess changes in community functionality across agroecosystems. We focused on carabids and spiders, because they are an important component of crop field biodiversity and have significant biological control potential.2. We assessed the effect of small-vs. large-scale agricultural landscapes, organic farming, and within-field position on functional diversity of spiders and carabids.We sampled pairs of organic and conventional winter wheat fields in small-scale agricultural landscapes (former West Germany) and in neighbouring large-scale agricultural landscapes (former East Germany). We sampled arthropods with funnel traps in transects at field edges, field interiors (15 m from edge), and field centres.3. The gradient from field edges towards the centres played an important role: spider body size decreased; ballooning ability increased, and hunting strategy switched from active hunters to more web-builders-presumably, due to higher microhabitat stability in the field centre. Higher trait diversity of spiders in field edges suggested higher biocontrol potential in small-scale agriculture. In contrast, carabid feeding switched from herbivores to carnivores, presumably due to higher pest densities inside crop fields. Furthermore, small-scale agricultural landscapes and organic management supported larger, i.e., less dispersive carabids. Synthesis and applications.In our research, spiders were more sensitive to edge effects and less sensitive to management and landscape composition than carabids. Smaller fields and longer edges, as well as organic management increase carabid functional diversity, which may increase resilience to environmental change. Since many spider species are confined to field edges, the effect of withinfield position on functional diversity is more important in small-scale agricultural landscapes with more edge habitat than in large-scale agricultural landscapes. Our findings suggest that European Union policy should acknowledge the high benefits of small-scale agriculture for the functional role of major predators such as spiders and carabid beetles, as the benefits are equal to those from a conversion to organic agriculture. 64 | Journal of Applied Ecology GALLÉ et AL.

Effects of landscape complexity and stand factors on arthropod communities in poplar forests

“…At the most effective scale, model averaging was performed using the function "model.avg" to produce averaged parameter estimates from the top model set (Gallé et al, 2018). The model-averaged results showed the relative importance (quantified by the sum of the Akaike weights associated with each variable in the models in the top model set) of the explanatory variables (Grueber et al, 2011).…”

“…Even though defoliators form the largest proportion of insect herbivores, most of them seldom cause mortality of trees (Kosola, Dickmann, Paul, & Parry, 2001). Many carabid beetles, lacewings, and all spiders are polyphagous predators and are widely used in biological control programs (Bertrand, Burel, & Baudry, 2016;Gallé et al, 2018). This may be due to the fact that local herdsmen mowed the aboveground plants regularly every year and even destroyed the poplar seedlings, coupled with the expansion of river closure lead to a significant decline of woodland, making forest landscape increasingly complex.…”

“…Recent findings have provided evidence that generalist natural enemies may be more effective than specialists in pest control (Björkman, Dalin, & Eklund, 2003;Chaplin-Kramer et al, 2011). Many carabid beetles, lacewings, and all spiders are polyphagous predators and are widely used in biological control programs (Bertrand, Burel, & Baudry, 2016;Gallé et al, 2018). An essential step toward effective biological control is to identify the important natural enemy species, and efficient biological control requires a landscape perspective because the surrounding landscape may provide alternative food sources, overwintering sites, and a refuge to natural enemies (Balzan et al, 2015;Björkman et al, 2003).…”

Predicting Landscape Configuration Effects on Agricultural Pest Suppression

“…In North America, edge density appears to have similar effects on aphid predators in cereal crops, with more chrysomelids, nabids, and overall higher aphid enemy richness in fine-grained landscapes [15,16]. However, results are inconsistent for some taxa, including coccinellids in soybeans and cereal grains [15,16,[20][21][22] and spiders [23][24][25][26] and carabids [13,22,24,27] in wheat and other crops.…”

Restoration trajectory of carabid functional traits in a formerly afforested blanket bog

“…Consequently, using a holistic approach that incorporates both taxonomic and functional biodiversity approaches (Fountain-Jones et al 2014), improves the understanding of how carabids respond to restoration in peatlands, and how this response affects other components of the ecosystem. In recent years, functional approaches have been particularly useful to improve our understanding of carabid ecology, and have been shown to be especially relevant in the study of carabid distribution (Magura 2017, Gallé et al 2019 and species flows (Magura & Lövei 2019) across habitat gradients, land use changes (Baulechner et al 2019) and trait syndromes associated with forests (Nolte et al 2017).…”