Higher trophic levels and species with poorer dispersal traits are more susceptible to habitat loss on island fragments

Ongoing habitat loss and fragmentation caused by human activities represents one of the greatest causes of biodiversity loss. However, the effects of habitat loss and fragmentation are not felt equally among species. Here, we examined how habitat loss influenced the diversity and abundance of species from different trophic levels, with different traits, by taking advantage of an inadvertent experiment that created habitat islands from a once continuous forest via the creation of the Thousand Island Lake, a large reservoir in China. On 28 of these islands with more than a 9000-fold difference in their area (0.12 ha to 1154 ha), we sampled plants, herbivorous insects and predatory insects using effort-controlled sampling and analyses. This allowed us to discern whether any observed differences in species diversity were due to passive sampling alone, or rather due to demographic effects that disproportionately influenced some species relative to others. We found that while most metrics of sampling effort-controlled diversity increased with island area, the strength of the effect was exacerbated for species in higher trophic levels. When we more explicitly examined differences in species composition among islands, we found that the pairwise difference in species composition among islands was dominated by species turnover, but that nestedness increased with differences in island area, indicating that some species are more likely to be absent from smaller islands. Furthermore, by examining trends of several dispersal-related traits of species, we found that species with lower dispersal propensity tended to be those that were lost from smaller islands, which was observed for herbivorous and predatory insects. Our results emphasize the importance of incorporating within-patch demographic effects, as well as the taxa and traits of species when understanding the influence of habitat loss on biodiversity.

人类活动引发的持续性生境丧失与破碎化，是生物多样性丧失的首要诱因之一。然而，不同物种所受生境丧失与破碎化的影响并不均等。本研究依托中国大型水库千岛湖（Thousand Island Lake）形成过程中，将原本连续的森林转化为生境岛的无意自然实验，探究了生境丧失如何影响不同营养级、不同功能性状物种的多样性与丰度。我们在其中28个岛屿（面积跨度达9000余倍，0.12公顷至1154公顷）上，采用控制采样强度的方案对植物、植食性昆虫与捕食性昆虫进行了采样与分析。这使得我们能够甄别：观测到的物种多样性差异究竟仅源于被动采样效应，还是源自相较于其他物种、对部分物种产生不成比例影响的种群动态效应。研究结果显示，尽管多数经采样强度校正后的多样性指标随岛屿面积增大而升高，但该效应在营养级更高的物种中表现得更为显著。当我们进一步细致分析岛屿间的物种组成差异时发现，岛屿间的物种组成成对差异主要由物种更替主导，但群落嵌套性随岛屿面积差异增大而升高，这表明部分物种更易在小型岛屿上缺失。此外，通过分析物种的若干扩散相关功能性状的变化趋势，我们发现扩散倾向较低的物种更易从小型岛屿中消失，该现象在植食性昆虫与捕食性昆虫中均有体现。本研究结果强调，在解析生境丧失对生物多样性的影响时，需纳入斑块内种群动态效应，同时兼顾物种类群与功能性状的差异。