Scale insects contribute to spider conservation in urban trees and shrubs

Urbanization filters arthropod communities and selects for species tolerant of urban conditions. Spiders are key generalist predators in urban ecosystems, but certain spider families are rare in cities compared to rural areas. The unique arthropod communities found in different tree species likely affect their ability to conserve spiders by providing different prey resources. If arthropods disperse from trees to plants growing below trees, the conservation benefits of the arthropod communities found in trees may also extend to plants growing beneath them. Certain urban tree species can host high densities of scale-insects and other arthropods that may provide important prey resources for spiders. To assess the conservation value of different arthropod communities in urban trees, we collected spiders from scale-infested and scale-uninfested trees and from shrubs under these trees. We used hanging cup traps to collect spiders that fell from both tree types. Spider abundance was greater within, and in shrubs below, scale-infested compared to scale-uninfested trees. Scale-infested trees hosted more orb web weaving spiders than scale-uninfested trees. Shrubs under scale-infested trees hosted more hunting, orb web weaving, and space web weaving spiders than shrubs under uninfested trees. Our findings suggest that scale-infested urban trees, and the robust arthropod communities they support, conserve certain spider guilds, and these benefits extend to other plants in the landscape. Implications for insect conservation: The ability of urban trees to conserve spider communities is in part attributable to the abundance of potential prey available within trees. Therefore, tolerating pests such as scale insects in urban trees can conserve spider communities both within trees and in shrubs planted below these trees.城市化进程会对节肢动物群落产生过滤筛选作用，筛选出能够耐受城市生境的物种。蜘蛛是城市生态系统中的关键广食性捕食者，但相较于乡村区域，城市中部分蜘蛛科类群较为稀缺。不同树种所承载的独特节肢动物群落，可通过提供各异的猎物资源，影响其保育蜘蛛的能力。若节肢动物从树木扩散至树下生长的植物，则树木所承载的节肢动物群落的保育效益，也可延伸至树下的其他植物。部分城市树种可承载高密度的介壳虫（scale-insects）及其他节肢动物，此类群可作为蜘蛛的重要猎物资源。为评估城市树木中不同节肢动物群落的保育价值，本研究从受介壳虫侵染与未受侵染的树木，以及这些树木下方的灌丛中采集蜘蛛样本。研究采用悬挂式杯形诱捕器，采集两类树木掉落的蜘蛛个体。相较于未受介壳虫侵染的树木，受侵染树木内部及其下方灌丛中的蜘蛛丰度更高。受介壳虫侵染的树木所承载的圆网织网蜘蛛类群，数量多于未受侵染的树木。受侵染树木下方的灌丛，相较于未侵染树木下方的灌丛，其承载的游猎型、圆网织网型及空间织网型蜘蛛类群更为丰富。本研究结果表明，受介壳虫侵染的城市树木及其所支撑的稳定节肢动物群落，可保育部分蜘蛛功能群，且该保育效益可延伸至景观中的其他植物。昆虫保育启示：城市树木对蜘蛛群落的保育能力，在一定程度上归因于树木内部可获取的潜在猎物资源丰度。因此，在城市树木中容忍介壳虫等害虫，可同时保育树木内部及其下方栽植灌丛中的蜘蛛群落。