Data from: Stability of a coevolving host-parasite system peaks at intermediate productivity

Habitat productivity may affect the stability of consumer-resource systems, through both ecological and evolutionary mechanisms. We hypothesize that coevolving consumer-resource systems show more stable dynamics at intermediate resource availability, while very low-level resource supply cannot support sufficiently large populations of resource and consumer species to avoid stochastic extinction, and extremely resource-rich environments may promote escalatory arms-race-like coevolution that can cause strong fluctuations in species abundance and even extinction of one or both trophic levels.We tested these ideas by carrying out an experimental evolution study with a model bacterium-phage system (Pseudomonas fluorescens SBW25 and its phage SBW25Φ2). Consistent with our hypothesis, this system was most stable at intermediate resource supply (fewer extinction events and smaller magnitude of population fluctuation). In our experiment, the rate of coevolution between bacterial resistance and phage infectivity was correlated with the magnitude of population fluctuation, which may explain the different in stability between levels of resource supply. Crucially, our results are consistent with a suggestion that, among the two major modes of antagonistic coevolution, arms race is more likely than fluctuation selection dynamics to cause extinction events in consumer-resource systems. This study suggests an important role of environment-dependent coevolutionary dynamics for the stability of consumer-resource species systems, therefore highlights the importance to consider contemporaneous evolutionary dynamics when studying the stability of ecosystems,particularly those under environmental changes.

生境生产力（habitat productivity）可通过生态与进化双重机制（ecological and evolutionary mechanisms），影响消费者-资源系统（consumer-resource systems）的稳定性。我们提出如下假说：协同进化（coevolution）的消费者-资源系统在中等资源可获得性（intermediate resource availability）条件下，动态更为稳定；极低的资源供给无法支撑足够规模的资源与消费者种群，难以避免随机灭绝（stochastic extinction）；而极端资源丰富的环境则可能催生升级式军备竞赛型协同进化（escalatory arms-race-like coevolution），引发种群丰度剧烈波动，甚至导致一个或两个营养级（trophic levels）的物种灭绝。我们借助模式细菌-噬菌体系统（model bacterium-phage system）开展实验进化研究（experimental evolution study），对上述假说进行了验证。实验结果与假说一致：该系统在中等资源供给条件下稳定性最高，表现为灭绝事件更少、种群波动幅度更小。本实验中，细菌抗性（bacterial resistance）与噬菌体侵染性（phage infectivity）之间的协同进化速率与种群波动幅度呈显著相关，这或可解释不同资源供给水平下系统稳定性的差异。尤为关键的是，我们的结果支持如下观点：在拮抗协同进化（antagonistic coevolution）的两大主要模式中，军备竞赛相较于波动选择动态（fluctuation selection dynamics），更易引发消费者-资源系统的灭绝事件。本研究揭示了依赖环境的协同进化动态对消费者-资源物种种群系统稳定性的重要作用，因此强调了在研究生态系统稳定性——尤其是处于环境变化中的生态系统——时，纳入同期进化动态（contemporaneous evolutionary dynamics）的重要性。