Linking Native and Invader Traits Explains Native Spider Population Responses to Plant Invasion

Theoretically, the functional traits of native species should determine how natives respond to invader-driven changes. To explore this idea, we simulated a large-scale plant invasion using dead spotted knapweed (Centaurea stoebe) stems to determine if native spiders’ web-building behaviors could explain differences in spider population responses to structural changes arising from C. stoebe invasion. After two years, irregular web-spiders were >30 times more abundant and orb weavers were >23 times more abundant on simulated invasion plots compared to controls. Additionally, irregular web-spiders on simulated invasion plots built webs that were 4.4 times larger and 5.0 times more likely to capture prey, leading to >2-fold increases in recruitment. Orb-weavers showed no differences in web size or prey captures between treatments. Web-spider responses to simulated invasion mimicked patterns following natural invasions, confirming that C. stoebe’s architecture is likely the primary attribute driving native spider responses to these invasions. Differences in spider responses were attributable to differences in web construction behaviors relative to historic web substrate constraints. Orb-weavers in this system constructed webs between multiple plants, so they were limited by the overall quantity of native substrates but not by the architecture of individual native plant species. Irregular web-spiders built their webs within individual plants and were greatly constrained by the diminutive architecture of native plant substrates, so they were limited both by quantity and quality of native substrates. Evaluating native species traits in the context of invader-driven change can explain invasion outcomes and help to identify factors limiting native populations.从理论层面而言，本土物种的功能性状应当决定其如何响应外来入侵引发的环境变化。为探究这一科学设想，本研究利用枯死的斑点矢车菊（Centaurea stoebe）茎秆开展大规模植物入侵模拟实验，旨在明确本土蜘蛛的结网行为能否解释蜘蛛种群对斑点矢车菊入侵所引发的生境结构变化的响应差异。实验开展两年后，相较于对照组样地，模拟入侵样地中的不规则结网蜘蛛种群丰度提升30倍以上，圆网蛛种群丰度则提升23倍以上。此外，模拟入侵样地内的不规则结网蜘蛛所结蛛网的面积增至对照组的4.4倍，猎物捕获概率提升至5.0倍，由此导致种群补充量提升2倍以上；而圆网蛛的结网面积与猎物捕获量在两组处理间均无显著差异。蜘蛛对模拟入侵的响应模式与自然入侵后的响应模式高度吻合，证实斑点矢车菊的形态结构或许是驱动本土蜘蛛响应此类入侵的核心属性。蜘蛛种群响应的差异，可归因于其结网行为相对于历史蛛网支撑基质约束的差异：本研究系统中的圆网蛛会在多株植物之间结网，因此其受限于本土支撑基质的整体总量，而非单一本土植物物种的形态结构；而不规则结网蜘蛛会在单株植物内部结网，其生存极大程度受限于本土植物支撑基质的小型化形态结构，因此同时受限于本土支撑基质的数量与质量。结合外来入侵引发的环境变化评估本土物种功能性状，能够解释植物入侵的生态结果，并有助于明确限制本土种群存续的关键因素。