Spider Communities And Biological Control In Brassica Fields:Integrating Field Ecology,Farming Practices,Landscape Complexity And Food Webs

Conservation biological control(CBC)places emphasis on natural and other non-crop vegetation as a source of natural enemies for focal crops.There is an unmet need for a definitive method to identify the type of vegetation optimal for supporting natural enemies to suppress pest arthropods in crops.Here I explore the commonality of the spider assemblage-considering abundance and diversity(H)-in Brassica fields with that of adjacent non-crop and non-Brassica vegetation.I employ spatial-based multivariate ordination approaches,hierarchical clustering and spatial eigenvector analyses.The small-scale mixed cropping and high disturbance frequency of southern Chinese farming offered a setting to test the role of vegetation in spider conservation.Our findings indicate that occurrence of spider families differ markedly with respect to vegetation type.Grassy field margins,non-crop vegetation(including the bushes,weeds and grasses),taro and sweetpotato harbour spider morphospecies and functional groups that are also present in Brassica fields.In contrast,pumpkin and litchi crops contain spiders that were not found in Brassica fields,and so have little benefit in vegetation management in Brassica fields.Our findings illustrate the utility of advanced statistical approaches for identifying spatial relationships between natural enemies and the land uses most likely to offer alternative habitats for CBC efforts and generates testable hypotheses for future studies.Agricultural intensification is a major cause of global biodiversity loss at the local and global scale.Local management and landscape structure affect biodiversity but how these scales interact to affect key ecosystem service providers is not well understood.Focusing on spiders,important providers of biological control,I tested the influence of local and landscape factors as filters of taxa,functional guilds and trait assemblages in Brassica fields.Multivariate ordination approaches and hierarchical clustering showed that local management practices,especially Brassica crop type,significantly effected the occurrence and assemblages of spider taxa and functional traits in Brassica fields.Local and landscape scale factors interacted such that organically managed white cabbage fields within complex landscapes support both taxonomically and functionally diverse spider communities including many web-builders.In contrast,pesticide-treated Chinese cabbage fields within simple landscapes,were dominated by ground runners with relatively lower body size but large femurs.These finding illustrated that Brassica fields under intense anthropogenic influence from local and landscape scale factors support functionally impoverished spider assemblages with low representation of ambush hunters and web-builders.Our findings indicate that local management scales and land covers drive the taxonomic and functional assemblages of spiders in ways that likely affect the delivery of a key ecosystem service.Sustainable management and conservation of biodiversity needs a comprehensive understanding of predator-prey interactions to ensure the coexistence of both predator and prey communities.Assessing the dietary range of generalist predators-spiders-in highly dynamic ecosystems by using conventional approaches,such as visual observation and conventional molecular approaches for prey detection often meets logistical problems.Therefore,I used high-throughput sequencing(HTS),advanced bioinformatic,statistical analyses and food webs to precisely analyze the prey DNA sequences and examine predator-prey trophic interactions in Brassica fields.These ecological community analysis and food webs approaches to analyze the predation of spiders confirmed that resource partitioning occurred in terms of abundance and diversity of prey taxa.The prey taxa in the gut of Araneidae,Lycosidae,Pisauridae,Salticidae and Thomisidae spiders were enriched with dipterans,coleopterans,hemipterans,lepidopterans and orthopterans along with a wide range of prey factions.These dietary patterns correspond well with the generalist foraging behavior of spiders and making them important taxa in encouraging and strengthening the biological control efforts in agroecosystems.Furthermore,HTS-based methods,advanced ecological community analyses and food webs can assist to explicate complex predator-prey interactions in highly dynamic ecosystems,which would facilitate the future studies on conservation of biodiversity.