Homeotherms and many poikilotherms display a positive relationship between body size and latitude, but this has rarely been investigated in microscopic animals. We analysed all published records of marine Tardigrada to address whether microscopic marine invertebrates have similar ecogeographical patterns to macroscopic animals. The data were analysed using spatially explicit generalized least squares models and linear models. We looked for latitudinal patterns in body size and species richness, testing for sampling bias and phylogenetic constraints. No latitudinal pattern was detected for species richness, and sampling bias was the strongest correlate of species richness. A hump-shaped increase in median body size with latitude was found, and the effect remained significant for the Northern Hemisphere but not for the Southern. The most significant effect supporting the latitudinal gradient was on minimum body size, with smaller species disappearing at higher latitudes. Our results suggest that biogeographical signals were observed for body size, albeit difficult to detect in poorly studied groups because of swamping from biased sampling effort and from low sample size. We did not find a significant correlation with the latitudinal pattern of body size and ecologically relevant net primary productivity.

中文翻译：

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海洋缓坡动物体中的纬度梯度

恒温和许多低温疗法在体型和纬度之间显示出正相关关系，但很少在微观动物中进行研究。我们分析了海洋Tardigrada的所有公开记录，以解决微观海洋无脊椎动物是否具有与宏观动物相似的生态地理模式。使用空间明确的广义最小二乘模型和线性模型分析数据。我们寻找体型和物种丰富度的纬度模式，测试抽样偏差和系统发育限制。没有检测到物种丰富度的纬度模式，并且采样偏差是物种丰富度的最强相关性。发现中位数随纬度呈驼峰状增长，对北半球的影响仍然显着，而对南半球的影响却不明显。支持纬度梯度的最显着效果是最小体型，较小物种在高纬度地区消失。我们的研究结果表明，尽管由于偏倚的采样工作量和较小的样本量而陷入困境，但在研究程度较差的人群中很难检测到生物地理信号，尽管难以检测。我们没有发现与体型的纬度格局和与生态有关的净初级生产力有显着相关性。