Data from: Life-history multistability caused by size-dependent mortality

Body size is a key determinant of mortality risk. In natural populations, a broad range of relationships are observed between body size and mortality, including positive and negative correlations. Previous evolutionary modelling has shown that negatively size-dependent mortality can result in life-history bistability, with early maturation at small size and late maturation at large size representing alternative fitness optima. Here we present a general analysis of conditions under which such life-history bistabilities can occur, reporting the following findings. First, alternative fitness optima can be found for any arbitrarily chosen forms of mortality functions, including functions according to which mortality smoothly declines with size. Second, while bistabilities occur more readily under negatively size-dependent mortality, our analysis reveals that they can also emerge under positively size-dependent mortality, a feature missed in earlier work. Third, any sharp drop of mortality with size facilitates bistability. Fourth, if the mortality regime involves more than one such sharp drop, multistable life histories can occur, with alternative fitness optima straddling each of the drops. Paradoxically, our findings imply that, fifth, a species-poor predator community capable of creating a 'rugged' mortality regime is conducive to evolutionary multistability, which could act as a stepping stone toward prey life-history diversification, whereas a species-rich predator community that results in a smoothly varying mortality regime may prevent diversification through this pathway.体型大小是决定死亡风险的关键因素。在自然种群中，体型与死亡间存在多样关联模式，涵盖正相关与负相关两类。过往进化建模研究表明，负体型依赖型死亡（negative size-dependent mortality）可引发生活史双稳态（life-history bistability），此时小型个体早熟与大型个体晚熟分别代表两种互斥的适应度最优解（fitness optima）。本研究针对此类生活史双稳态的发生条件开展一般性分析，得到如下结论：其一，无论选取任意形式的死亡函数（mortality functions），包括死亡随体型平滑下降的函数，均可找到互斥的适应度最优解；其二，尽管负体型依赖型死亡环境下双稳态更易出现，但本研究分析显示，正体型依赖型死亡（positive size-dependent mortality）环境下同样可产生双稳态，这一特征在过往研究中被忽略；其三，死亡随体型出现的任何急剧下降均会促进双稳态的产生；其四，若死亡模式（mortality regime）包含多个此类急剧下降点，则可出现多稳态生活史（multistable life histories），且每个下降点对应一组互斥的适应度最优解；第五，颇具悖论性的是，本研究结论表明，能够形成‘崎岖型’死亡模式（rugged mortality regime）的物种贫乏捕食者群落，有助于进化多稳态（evolutionary multistability）的产生，而这可作为推动猎物生活史多样化的契机；与之相反，由物种丰富捕食者群落导致的平滑变化死亡模式，则可能通过该路径阻碍物种多样化。