1. The temperature‐size rule (TSR) describes the inverse relationship between organism size and environmental temperature in uni‐ and multicellular species. Despite the TSR being widespread, the mechanisms for shrinking body size with warming remain elusive.
2. Here, we experimentally test three hypotheses (differential development and growth [DDG], maintain aerobic scope and regulate oxygen supply [MASROS] and the supply–demand [SD] hypothesis) potentially explaining the TSR using the aquatic protist Colpidium striatum in three gradually changing and one constant temperature environment crossed with three different nutrient levels.
3. We find that the constant and slowly warming environments show similar responses in terms of population dynamics, whereas populations with linear and fast warming quickly decline and show a stronger temperature‐size response.
4. Our analyses suggest that acclimation may have played a role in observing these differences among treatments. The SD hypothesis is most parsimonious with the data, however, neither the DDG nor the MASROS hypothesis can be firmly dismissed. We conclude that the TSR is driven by multiple ecological and acclimatory responses, hence multicausal.

中文翻译：

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使用非线性温度增加测试温度大小规则的多个驱动因素

1. 温度大小规则（TSR）描述了单细胞和多细胞物种中生物体大小与环境温度之间的反比关系。尽管TSR广泛使用，但随着加热而缩小车身尺寸的机制仍然难以捉摸。
2. 在这里，我们通过实验检验三个假设（差异发育和生长[DDG]，维持有氧范围并调节供氧[MASROS]和供需[SD]假设），这可能会使用水生原生质体纹状体在三个逐渐变化的环境中解释TSR。和一个恒温环境，其中三种营养水平不同。
3. 我们发现恒定和缓慢变暖的环境在种群动态方面表现出相似的响应，而线性变暖和快速变暖的种群迅速下降并表现出更强的温度大小响应。
4. 我们的分析表明，适应可能在观察治疗之间的这些差异方面发挥了作用。SD假设与数据最相似，但是DDG假设和MASROS假设都不能被坚决驳斥。我们得出的结论是，TSR由多种生态和适应性反应驱动，因此是多因果关系的。