Eco-evolutionary feedbacks predict the time course of rapid life history evolution

Organisms can change their environment and, in so doing, change the selection they experience and how they evolve. Population density is one potential mediator of such interactions because high population densities can impact the ecosystem and reduce resource availability. At present, such interactions are best known from theory and laboratory experiments. Here we quantify the importance of such interactions in nature by transplanting guppies from a stream where they co-occur with predators into tributaries that previously lacked both guppies and predators. If guppies evolve solely because of the immediate reduction in mortality rate, the strength of selection and rate of evolution should be greatest at the outset then decline as the population adapts to its new environment. If indirect effects caused by the increase in guppy population density in the absence of predation prevail, then there should be a lag in guppy evolution because time is required for them to modify
their environment. The duration of this lag is predicted to be associated with the environmental modification caused by guppies. We observed a lag in life history evolution associated with increases in population density and altered ecology. How guppies evolved matched predictions derived from evolutionary theory that incorporates such density effects.

生物可以改变自身所处的环境，并借此改变其所经历的选择压力及其演化路径。种群密度是这类相互作用的潜在调控因子之一，因为较高的种群密度会对生态系统造成影响并降低资源可获得性。目前，这类相互作用的相关认知主要源自理论研究与室内实验。在本研究中，我们通过将花鳉（guppies）从其与捕食者共存的溪流，移植到此前既无花鳉也无捕食者的支流中，量化了这类相互作用在自然环境中的重要性。若花鳉的演化仅源于死亡率的直接下降，则选择强度与演化速率应在初始阶段达到峰值，随后随着种群适应新环境而逐渐降低。若在无捕食压力的情况下，由花鳉种群密度升高所引发的间接效应占据主导，则花鳉的演化将出现滞后——因为它们需要一定时间来改造自身所处的环境。该滞后的持续时长，预计与花鳉所引发的环境改造效应相关。我们观测到与种群密度升高及生态系统改变相关的生活史演化滞后现象，花鳉的演化模式完全符合纳入了密度效应的演化理论所作出的预测。