Data from: Towards a mechanistic understanding of thermal niche partitioning

We develop a theoretical framework to elucidate the mechanistic basis of thermal niche partitioning in ectotherms. Using a food web module of two consumers competing for a biotic resource, we investigate how temperature effects on species' attack and mortality rates scale up to population-level outcomes of coexistence and exclusion. We find that species' differences in competitive effects arise from asymmetries generated by the non-linear temperature response of mortality: cold-adapted species experience stronger intra-specific competition than warm-adapted species; they also exert weaker competition on, and experience stronger competition from, warm-adapted species. These asymmetries become greater as seasonal fluctuations increase, generating latitudinal variation in coexistence and priority effects. Characterizing species' thermal niches in terms of mechanistic descriptions of trait responses allows for testable predictions about population-level competitive outcomes based solely on three fundamental, and easily measurable, quantities: attack rate optima, response breadths and temperature sensitivity of mortality. We test our predictions with data from an insect host-parasitoid community. By quantifying the three basic quantities we predict that priority effects cannot occur, which is borne out by population-level experiments showing that the outcome of competition does not depend on initial conditions. More broadly, our framework can predict the conditions under which exotic invasive species can exclude, or coexist with, native biota, and the effects of climate warming on competitive communities across latitudinal gradients.

我们构建了一套理论框架，以阐明外温动物（ectotherms）的热生态位分区机制基础。本研究采用以生物资源为竞争对象的双消费者食物网模块（food web module），探究温度对物种攻击率与死亡率的影响如何逐级推演至种群层面的共存与竞争排除结局。研究发现，物种间竞争效应的差异源于死亡率的非线性温度响应所产生的不对称性：耐寒物种较适温物种面临更强的种内竞争；同时，耐寒物种对适温物种的竞争抑制作用更弱，且自身受到适温物种的更强竞争压力。这些不对称性随季节波动加剧而愈发显著，进而引发共存与优先效应（priority effects）的纬度变异。通过对性状响应的机制性描述来表征物种的热生态位，仅需三个基础且易于测量的量——攻击率最适值、响应幅度以及死亡率的温度敏感性——即可对种群层面的竞争结果做出可验证的预测。我们利用昆虫寄主-寄生蜂（host-parasitoid）群落的数据集对上述预测进行了验证。通过量化这三个基本量，我们预测优先效应不会出现，而种群水平的实验结果也证实了这一点：竞争结果并不依赖于初始种群条件。更广泛地说，本框架可预测外来入侵物种（exotic invasive species）排挤或与本地生物区系（native biota）共存的条件，以及气候变暖对沿纬度梯度分布的竞争群落的影响。