Data from: Temperature-related variation in growth rate, size, maturation, and lifespan in a marine herbivorous fish over a latitudinal gradient

1. In ectotherms, growth rate, body size, and maturation rate co-vary with temperature, with the direction and magnitude of variation predicted by the Temperature-Size Rule (TSR). Nutritional quality or availability of food, however, may vary over latitudinal gradients, resulting in ambiguous effects on body size and maturation rate. The Temperature-Constraint Hypothesis (TCH) predicts that marine herbivorous ectotherms are nutritionally compromised at latitudes exceeding 30o. This provides an opportunity to resolve the contrasting demographic responses of ectotherms to variation in temperature and nutritional status over latitudinal gradients. 2. This study uses analysis of demographic rates to evaluate the predictions of the TSR in a marine herbivorous ectotherm sampled over a significant latitudinal gradient. 3. The direction and magnitude of demographic variation was established in the marine herbivorous fish, Odax pullus (the butterfish), and compared with that of a phylogenetically related but trophically distinct species, the carnivorous Notolabrus fucicola (the banded wrasse). Both species were sampled at three locations across the length of New Zealand covering latitudes between 35oS and 49oS. Growth rate, mean size-at-age, age- and size-at-maturity, lifespan, and abundance were estimated for each species at each location. 4. Demographic traits of both taxa varied with latitude. Both species showed slower initial growth rates, and matured later at a larger body size at higher latitudes than populations sampled at lower latitudes. In addition, abundances increased significantly at higher latitudes in both species. 5. These results were consistent with the TSR but not the TCH, confirming that nutritional ecology (herbivore vs. carnivory) did not determine demographic patterns over a biologically significant latitudinal gradient. Results from this study suggest that the absence of herbivorous reef fishes from the higher latitudes of the northern hemisphere may not reflect a general physiological mechanism as suggested by the TCH, and highlights the need to clarify the evolutionary histories of the marine biotas of each hemisphere.

1. 变温动物（ectotherms）的生长速率、体型大小与成熟速率均随温度发生协同变化，其变化方向与幅度可通过温度-体型法则（Temperature-Size Rule, TSR）进行预测。然而食物的营养质量或可获得性会随纬度梯度发生改变，进而对体型大小与成熟速率产生难以明确的影响。温度约束假说（Temperature-Constraint Hypothesis, TCH）预测，海洋植食性变温动物在纬度超过30°的区域会面临营养供给不足的问题。这为解析变温动物沿纬度梯度对温度与营养状态变化的差异化种群动态响应提供了研究契机。
2. 本研究通过分析种群动态速率，对沿显著纬度梯度采样的海洋植食性变温动物的TSR预测进行验证。
3. 研究以海洋植食性鱼类奥氏盔鱼（Odax pullus，黄油鱼）为对象，明确其种群动态变异的方向与幅度，并将其与系统发育亲缘关系相近但营养策略迥异的肉食性物种带纹濑鱼（Notolabrus fucicola，带纹隆头鱼）进行对比。研究团队在横贯新西兰全境的三个采样点开展工作，覆盖了35°S至49°S的纬度范围。针对每个采样点的两个物种，均估算了其生长速率、年龄别平均体型、成熟时的年龄与体型、寿命以及种群丰度。
4. 两个类群的种群动态特征均随纬度发生变化。相较于低纬度采样种群，高纬度种群的初始生长速率更慢，且成熟时间更晚、体型更大。此外，两个物种的种群丰度在高纬度区域均出现显著上升。
5. 本研究结果符合TSR的预测，但与TCH的假说不符，证实营养生态分化（植食性与肉食性的差异）并未在具有生物学意义的纬度梯度上决定种群动态模式。本研究结果表明，北半球高纬度区域缺乏植食性礁栖鱼类的现象，或许并不像TCH所提出的那样源于普遍的生理机制，同时也凸显了厘清各半球海洋生物群系进化历史的必要性。