Management intensity and vegetation complexity affect web-building spiders and their prey

Abstract

Agricultural management and vegetation complexity affect arthropod diversity and may alter trophic interactions between predators and their prey. Web-building spiders are abundant generalist predators and important natural enemies of pests. We analyzed how management intensity (tillage, cutting of the vegetation, grazing by cattle, and synthetic and organic inputs) and vegetation complexity (plant species richness, vegetation height, coverage, and density) affect rarefied richness and composition of web-building spiders and their prey with respect to prey availability and aphid predation in 12 habitats, ranging from an uncut fallow to a conventionally managed maize field. Spiders and prey from webs were collected manually and the potential prey were quantified using sticky traps. The species richness of web-building spiders and the order richness of prey increased with plant diversity and vegetation coverage. Prey order richness was lower at tilled compared to no-till sites. Hemipterans (primarily aphids) were overrepresented, while dipterans, hymenopterans, and thysanopterans were underrepresented in webs compared to sticky traps. The per spider capture efficiency for aphids was higher at tilled than at no-till sites and decreased with vegetation complexity. After accounting for local densities, 1.8 times more aphids were captured at uncut compared to cut sites. Our results emphasize the functional role of web-building spiders in aphid predation, but suggest negative effects of cutting or harvesting. We conclude that reduced management intensity and increased vegetation complexity help to conserve local invertebrate diversity, and that web-building spiders at sites under low management intensity (e.g., semi-natural habitats) contribute to aphid suppression at the landscape scale.

Soil management shapes ecosystem service provision and trade-offs in agricultural landscapes

“…This confirms previous studies that have shown how arthropod predators are influenced by decreased tillage disturbance [9,34]. For example, spider colonization and establishment have been shown to be favoured under conservation tillage due to the higher soil environment stability and weed density, which promotes a deeper litter and more structurally complex vegetation [4,35]. Aphid parasitism rate showed, instead, no difference between tillage systems.…”

The use of DNA barcodes in food web construction—terrestrial and aquatic ecologists unite!

“…2B; see references in Food web structure is affected by resolution). Interaction strength is often unquantified (from Summerhayes andElton 1923 through Cohen et al 1990 to Wirta et al 2015b), inferred from sometimes limited and always laborious observations of direct attacks (Carnicer et al 2009) or through methods with an only indirect link to realized predation and consumption rates (Frost 1972;Nyffeler 1999;Diehl et al 2013;Majaneva et al 2014). …”

Habitat associations of epigeal spiders in upland calcareous grassland landscapes: the importance for conservation

“…They encompass a wide range of foraging strategies and as such are differentially sensitive to variations in vegetation architecture and disturbance (Barriga et al 2010;Dielh et al 2013;Gibson et al 1992). Differences in foraging strategies are linked to vegetation structure and disturbance (Alderweireldt 1994;Bell et al 2001;Uetz 1991).…”

“…Differences in foraging strategies are linked to vegetation structure and disturbance (Alderweireldt 1994;Bell et al 2001;Uetz 1991). Ground hunting species require a heterogeneous sward of open patches to search for prey and taller vegetation for refuge (Maelfait and De Keer 1990), whereas orb web weaving spiders select structurally complex vegetation that provides increased web anchorage points (Dielh et al 2013;Langellotto and Denno 2004;McNett and Rypstra 2000). The differences in foraging strategy, activity and substrate utilisation amongst species make grouping spiders into guilds a useful tool for examining functional differences among habitats (Corcuera et al 2015;Schweiger et al 2005).…”