Interspecific competition counteracts negative effects of dispersal on adaptation of an arthropod herbivore to a new host

Dispersal and competition have both been suggested to drive variation in adaptability to a new environment, either positively or negatively. A simultaneous experimental test of both mechanisms is however lacking. Here, we experimentally investigate how population dynamics and local adaptation to a new host plant in a model species, the two-spotted spider mite (Tetranychus urticae), are affected by dispersal from a stock population (no-adapted) and competition with an already adapted spider mite species (Tetranychus evansi). For the population dynamics, we find that competition generally reduces population size and increases the risk of population extinction. However, these negative effects are counteracted by dispersal. For local adaptation, the roles of competition and dispersal are reversed. Without competition, dispersal exerts a negative effect on adaptation (measured as fecundity) to a novel host and females receiving the highest number of immigrants performed similarly to the stoc...

扩散与竞争均被认为可正向或负向调控生物对新环境的适应性变异。然而，目前尚缺乏同时检验这两种作用机制的实验研究。本研究以模式物种二斑叶螨（Tetranychus urticae）为研究对象，通过实验探究来自未适应原种群的扩散，以及与已适应的神泽氏叶螨（Tetranychus evansi）的种间竞争，如何影响其种群动态以及对新寄主植物的局部适应性。在种群动态方面，研究发现竞争通常会降低种群规模并提升种群灭绝风险，但此类负面效应可通过扩散得到缓解。而就局部适应性而言，竞争与扩散的作用效果恰好相反：在无竞争条件下，扩散对生物在新寄主上的适应性（以繁殖力为衡量指标）产生负向影响，接收移民数量最多的雌性个体其表现与原种群个体相似……