McNamara John M, Higginson Andrew D, Verhulst Simon
School of Mathematics University of Bristol Bristol BS8 1TW UK.
Centre for Research in Animal Behaviour College of Life and Environmental Sciences University of Exeter Exeter EX4 4QG UK; School of Biological Sciences University of Bristol Bristol BS8 1TQ UK.
J Biogeogr. 2016 Apr;43(4):809-819. doi: 10.1111/jbi.12695. Epub 2015 Dec 22.
The tendency for animals at higher latitudes to be larger (Bergmann's rule) is generally explained by recourse to latitudinal effects on ambient temperature and the food supply, but these receive only mixed support and do not explain observations of the inverse to Bergmann's rule. Our aim was to better understand how ecological variables might influence body size and thereby explain this mixed support.
World-wide.
Previous explanations do not allow for the selective pressure exerted by the trade-off between predation and starvation, which we incorporate in a model of optimal body size and energy storage of a generalized homeotherm. In contrast to existing arguments, we concentrate on survival over winter when the food supply is poor and can be interrupted for short periods.
We use our model to assess the logical validity of the heat conservation hypothesis and show that it must allow for the roles of both food availability and predation risk. We find that whether the effect of temperature on body size is positive or negative depends on temperature range, predator density, and the likelihood of long interruptions to foraging. Furthermore, changing day length explains differing effects of altitude and latitude on body size, leading to opposite predictions for nocturnal and diurnal endotherms. Food availability and ambient temperature can have counteracting selective pressures on body mass, and can lead to a non-monotonic relationship between latitude and size, as observed in several studies.
Our work provides a theoretical framework for understanding the relationships between the costs and benefits of large body size and eco-geographical patterns among endotherms world-wide.
高纬度地区动物体型更大的趋势（伯格曼法则）通常归因于纬度对环境温度和食物供应的影响，但这些因素仅得到部分支持，且无法解释与伯格曼法则相反的观察结果。我们的目的是更好地理解生态变量如何影响体型，从而解释这种不一致的支持情况。
全球。
以往的解释未考虑捕食与饥饿之间权衡所产生的选择压力，我们将其纳入一个广义恒温动物最佳体型和能量储存的模型中。与现有观点不同，我们关注食物供应匮乏且可能短期中断的冬季生存情况。
我们用模型评估了热量守恒假说的逻辑有效性，结果表明该假说必须考虑食物可获得性和捕食风险的作用。我们发现温度对体型的影响是正还是负取决于温度范围、捕食者密度以及觅食长期中断的可能性。此外，日照时长的变化解释了海拔和纬度对体型的不同影响，这导致对夜行性和昼行性恒温动物的预测相反。食物可获得性和环境温度对体重可能产生相互抵消的选择压力，并可能导致纬度与体型之间呈现非单调关系，这在多项研究中都有观察到。
我们开展的研究为理解全球恒温动物中大体型的成本与收益之间的关系以及生态地理模式提供了一个理论框架。
