The relationship between productivity and diversity is controversial because of disparity between unimodal and monotonic patterns, especially when occurring simultaneously at different scales. We used stream-side artificial channels to investigate how the availability of a major resource (leaf litter) affected stream invertebrate abundance and diversity at leaf-pack and whole-channel scales. At the larger scale, invertebrate diversity increased monotonically with increasing litter resource density, whereas at the smaller scale the relationship was hump-shaped, in keeping with reports in the literature. This divergence at higher resource levels suggests that multiple mechanisms may be operating. Our results indicate that consistently high species turnover (β diversity) caused the monotonic pattern because of a species-area or “sampling effect” in which new species accumulate with increasing number of samples. The hump-shaped pattern was due to constrained immigration because of a “dilution effect” in which a limited number of immigrants is spread out among the increasing number of available patches. We propose that the relationship between productivity or resource availability and α diversity is generally hump-shaped and the scale-dependent contrast in the relationship only arises where the species pool is large and β diversity is high. Differences in β diversity may, therefore, explain some of the contrasting patterns in the productivity–diversity relationship previously reported.We suggest that continuing immigration by rare taxa is important in sustaining species diversity when productivity is high. The hump-shaped pattern has implications for the impact of anthropogenic ecosystem enrichment on species diversity.

生产力与多样性之间的关系是有争议的，因为单峰模式和单调模式之间存在差异，尤其是在同时发生于不同规模时。我们使用河流侧人工渠道调查了主要资源（枯枝落叶）的可用性如何在叶丛和全渠道尺度上影响河流无脊椎动物的丰度和多样性。在较大规模上，无脊椎动物多样性随凋落物资源密度的增加而单调增加，而在较小规模上，这种关系呈驼峰状，与文献报道一致。在较高资源级别上的这种差异表明可能正在运行多种机制。我们的结果表明，由于物种面积或“采样效应”（其中新物种随着样本数量的增加而积累），持续较高的物种更新（β多样性）导致单调模式。驼峰形的图案是由于“稀释效应”而限制了移民，在有限的移民中，有限的移民散布在越来越多的可用斑块中。我们认为生产力或资源可用性与α多样性之间的关系通常呈驼峰状，并且仅当物种库很大且β多样性较高时才会出现比例相关的对比。因此，β多样性的差异可以解释先前报道的生产率与多样性关系中的一些对比模式。我们建议，在高生产力的情况下，通过稀有分类单元继续移民对于维持物种多样性很重要。驼峰形模式对人为生态系统富集对物种多样性的影响具有影响。