Data from: Nonlinear thermal gradients shape broad-scale patterns in geographic range size and can reverse Rapoport’s rule

Aim: Species living at latitudes that have greater annual temperature variations are expected to achieve broader geographic ranges than species living at latitudes that have smaller annual temperature variations, generating a positive relationship between range size and latitude (Rapoport's rule). However, this prediction fails to take into account the greater latitudinal extent of tropical temperatures relative to those at higher latitudes. Here we model the contributions of the broader latitudinal extent of equal-temperature habitats at low latitudes and the greater annual temperature variation at high latitudes to the range size–latitude relationship, and test whether the latitudinal variation in geographic range size in marine bivalves can be explained by models that account for both annual temperature variation and the steepness of latitudinal thermal gradients. Location: Western Pacific, eastern Pacific and western Atlantic. Methods: We use a null model where geographic ranges are placed on the ocean surface independently of thermal gradients, and a range-expansion model where the minimum and maximum temperatures encompassed by the geographic range of a species (macroecological thermal ranges) are positively related to annual temperature minima and maxima at the location where the species originated. We compare results with a database containing 40,820 occurrences of 4760 marine bivalve species. Result: Models incorporating temperature-limited range expansion along realistic thermal gradients predict an inverse relationship between range size and latitude, in opposition to Rapoport's rule. The distribution patterns of marine bivalves match this prediction. Main conclusions: The poleward trend in latitudinal range size is determined by the nonlinearity of the latitudinal gradient of temperature minima and maxima and less by the latitudinal gradient of the local seasonal range in temperatures. Although tropical species do have narrower macroecological thermal ranges than high-latitude species, the nearly constant temperatures over wide areas of the tropics allow tropical species to achieve broad latitudinal ranges.研究目的：相较于年温度波动幅度更小的纬度区域的物种，栖息于年温度波动幅度更大的纬度区域的物种，其地理分布范围往往更广，由此会形成分布范围大小与纬度之间的正相关关系（拉波波特法则（Rapoport's rule））。然而，这一预测未考虑热带温度相较于高纬度温度具有更大的纬度跨度。本研究针对低纬度地区等温生境的更大纬度跨度，以及高纬度地区更大的年温度波动，对分布范围大小与纬度的关系的贡献进行建模，并检验海洋双壳类（marine bivalves）的地理分布范围大小的纬度差异，是否可以通过同时考虑年温度波动与纬度热梯度陡峭程度的模型得到解释。 研究区域：西太平洋、东太平洋与西大西洋。 研究方法：我们采用两种模型，其一为零模型（null model），即地理分布范围独立于热梯度放置于海洋表面；其二为分布扩张模型（range-expansion model），即物种地理分布范围所涵盖的最低与最高温度（宏观生态热范围（macroecological thermal ranges）），与物种起源地的年温度最小值、最大值呈正相关关系。我们将模型结果与包含4760种海洋双壳类的40820条物种出现记录的数据库进行对比。 研究结果：纳入基于真实热梯度的温度限制型分布扩张的模型，预测得到分布范围大小与纬度之间呈负相关关系，这与拉波波特法则相悖。海洋双壳类的分布格局与该预测相符。 主要结论：纬度分布范围的向极变化趋势，由温度最小值与最大值的纬度梯度非线性性所决定，而非由局地温度季节波动的纬度梯度主导。尽管热带物种的宏观生态热范围确实窄于高纬度物种，但热带广阔区域内近乎恒定的温度，使得热带物种能够拥有广阔的纬度分布范围。