Trophic cascades alter eco-evolutionary dynamics and body size evolution

Trait evolution in predator-prey systems can feed back to the dynamics of interacting species as well as cascade to impact the dynamics of indirectly linked species (eco-evolutionary trophic cascades; EETC). A key mediator of trophic cascades is body mass, as it both strongly influences and evolves in response to predator-prey interactions. Here we use Gillespie Eco-Evolutionary Models to explore EETCs resulting from top predator loss and mediated by body mass evolution. Our four trophic level food chain model uses allometric scaling to link body mass to different functions (ecological pleiotropy) and is realistically parameterized from the FORAGE database to mimic the parameter space of a typical freshwater system. To track real-time changes in selective pressures, we also calculated fitness gradients for each trophic level. As predicted, top predator loss generated alternating shifts in abundance across trophic levels, and depending on the nature and strength in changes to fitness gradients, also altered trajectories of body mass evolution. Although more distantly linked, changes in the abundance of top predators still affected the eco-evolutionary dynamics of the basal producers, in part because of their relatively short generation times. Overall, our results suggest that impacts on top predators can set off transient eco-evolutionary trophic cascades with the potential for widespread indirect impacts on food webs.

Methods
MatLab files used to create eco-evolutionary trophic cascades in the GEM model.

捕食者-猎物系统中的性状演化，既可反馈调控互作物种种群动态，也可级联影响间接关联物种种群动态，此类现象被命名为生态演化营养级联（eco-evolutionary trophic cascades, EETC）。营养级联的关键介导因子为体型质量，其既强烈受捕食者-猎物互作影响，也会随此类互作发生演化。本研究采用吉莱斯皮生态演化模型（Gillespie Eco-Evolutionary Models），探究由顶级捕食者丧失引发、以体型质量演化为介导的生态演化营养级联。我们构建的四营养级食物链模型，通过异速缩放关系将体型质量与多种功能相联结（生态多效性），并基于FORAGE数据库进行现实化参数化，以复刻典型淡水生态系统的参数空间。为追踪选择压力的实时动态变化，我们还计算了各营养级的适合度梯度。正如研究预期，顶级捕食者的丧失引发了营养级间丰度的交替波动；且依据适合度梯度变化的性质与强度，体型质量演化的轨迹也会发生改变。尽管基础生产者与顶级捕食者的关联相对间接，但前者的生态演化动态仍受顶级捕食者丰度变化的影响，这在一定程度上源于其世代时长相对较短。总体而言，本研究结果表明，对顶级捕食者的干扰可触发瞬态生态演化营养级联，进而可能对食物网产生广泛的间接影响。

方法：用于在吉莱斯皮生态演化模型中构建生态演化营养级联的MatLab文件。