Activity density (AD), the rate that an individual taxon or its biomass moves through the environment, is used both to monitor communities and quantify the potential for ecosystem work. The Abundance Velocity Hypothesis posited that AD increases with aboveground net primary productivity (ANPP) and is a unimodal function of temperature. Here we show that, at continental extents, increasing ANPP may have nonlinear effects on AD: increasing abundance, but decreasing velocity as accumulating vegetation interferes with movement. We use 5 yr of data from the NEON invertebrate pitfall trap arrays including 43 locations and four habitat types for a total of 77 habitat–site combinations to evaluate continental drivers of invertebrate AD. ANPP and temperature accounted for one-third to 92% of variation in AD. As predicted, AD was a unimodal function of temperature in forests and grasslands but increased linearly in open scrublands. ANPP yielded further nonlinear effects, generating unimodal AD curves in wetlands, and bimodal curves in forests. While all four habitats showed no AD trends over 5 yr of sampling, these nonlinearities suggest that trends in AD, often used to infer changes in insect abundance, will vary qualitatively across ecoregions.

中文翻译：

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大陆尺度的活动密度：是什么驱动无脊椎动物生物量在土壤表面移动？

活动密度 (AD)，即单个分类单元或其生物量在环境中移动的速率，用于监测群落和量化生态系统工作的潜力。丰度速度假设假设 AD 随着地上净初级生产力 (ANPP) 的增加而增加，并且是温度的单峰函数。在这里，我们表明，在大陆范围内，增加 ANPP 可能对 AD 产生非线性影响：增加丰度，但随着植被的积累干扰运动，速度降低。我们使用来自 NEON 无脊椎动物陷阱阵列的 5 年数据，包括 43 个位置和四种栖息地类型，共 77 个栖息地-地点组合，以评估大陆无脊椎动物 AD 的驱动因素。ANPP 和温度占 AD 变异的三分之一到 92%。正如预测的那样，AD 是森林和草原温度的单峰函数，但在开阔的灌丛中呈线性增加。ANPP 产生了进一步的非线性效应，在湿地中产生单峰 AD 曲线，在森林中产生双峰曲线。虽然所有四个栖息地在 5 年的采样中都没有显示出 AD 趋势，但这些非线性表明，通常用于推断昆虫丰度变化的 AD 趋势在不同生态区域之间会发生质的变化。