Butterfly nectar foraging and flowering plant community data from field surveys in Victoria, British Columbia, Canada

AbstractThe negative impacts of non-native species have been well documented, but some non-natives can play a positive role in native ecosystems. One way that non-native plants can positively interact with native butterflies is by provisioning nectar. Relatively little is known about the role of phenology in determining native butterfly visitation to non-native plants for nectar, yet flowering time directly controls nectar availability. Here, we investigate the phenological patterns of flowering by native and non-native plants and nectar foraging by native butterflies in an oak savanna on Vancouver Island, British Columbia, Canada. We also test whether native butterflies select nectar sources in proportion to their availability. We found that non-native plants were well integrated into butterfly nectar diets (83% of foraging observations) and that visitation to non-natives increased later in the season when native plants were no longer flowering. We also found that butterflies selected non-native flowers more often than expected based on their availability, suggesting that these plants represent a potentially valuable resource. Our study shows that non-native species have the potential to drive key species interactions in seasonal ecosystems. Management regimes focused on eradicating non-native species may need to re-consider their aims and evaluate resources that non-natives provide.
MethodsData was collected from 10 sites of Garry oak savanna in Victoria, British Columbia, Canada that were visited in rotation from May to August 2019. At the start of each visit to a site, two observers recorded butterfly nectar foraging for 60–90 minutes by walking a 300 m long route. When foraging occurred, the species of butterfly and flowering plant were recorded. Next, we estimated flower availability from all flowering forbs and shrubs either on the same or following day as the butterfly surveys by placing a 1 m2 habitat quadrat at five random locations along the same 300 m route. Within each quadrat, we counted the number of open flowering units for each plant species. We also estimated the mean floral surface area for each flowering plant species observed across the season by measuring the dimensions of 10-20 individuals per species. Thus, flower availability was calculated by multiplying the number of flowering units counted with their mean floral surface area for each species during each visit to a site.

摘要 外来物种的负面影响已有充分文献记载，但部分外来物种可对本土生态系统发挥积极作用。外来植物可通过提供花蜜，与本土蝴蝶形成正向互作关系。目前针对物候如何调控本土蝴蝶访食非本土植物花蜜的作用机制，相关研究仍相对匮乏，而开花时间直接决定了花蜜的可获得性。本研究于加拿大不列颠哥伦比亚省温哥华岛的一处葛瑞橡树稀树草原（Garry oak savanna）中，探究了本土与外来植物的开花物候模式，以及本土蝴蝶的花蜜觅食物候特征。同时本研究检验了本土蝴蝶是否会依据资源可获得性的比例来选择花蜜来源。研究结果显示，外来植物已深度融入蝴蝶的花蜜采食食谱（占觅食观测记录的83%），且当本土植物花期结束进入季末时，蝴蝶对非本土植物的访花频次显著升高。此外，相较于基于资源可获得性的预期，蝴蝶对非本土花的访视频次更高，表明这类植物是极具价值的花蜜资源。本研究表明，外来物种有潜力在季节性生态系统中调控关键物种互作。旨在根除外来物种的管理方案或许需要重新考量其目标，并评估外来物种所提供的生态资源。

方法 本研究数据采集自加拿大不列颠哥伦比亚省维多利亚市的10处葛瑞橡树稀树草原样地，调查周期为2019年5月至8月，各站点轮流开展观测。每次到访样地伊始，2名观测者沿300米长的样线步行，开展60至90分钟的蝴蝶花蜜觅食行为观测。若观测到觅食行为，则记录蝴蝶与开花植物的物种。随后，在蝴蝶调查当日或次日，沿同一条300米样线的5个随机点位放置1平方米的生境样方（habitat quadrat），以此估算所有开花草本与灌木的花蜜资源可获得性。在每个样方内，统计每种植物的开放开花单元数量。此外，本研究通过测量本季观测到的每种开花植物的10至20个个体的花部尺寸，估算该物种的平均花表面积（floral surface area）。因此，每次样地调查时的花蜜可获得性，可通过将每种植物的开放开花单元数量与其平均花表面积相乘计算得到。