Johansson Jacob
Department of Theoretical Ecology, Ecology Building, Lund University, SE-22362 Lund, Sweden.
Evolution. 2008 Feb;62(2):421-35. doi: 10.1111/j.1558-5646.2007.00301.x. Epub 2007 Nov 19.
The role and importance of ecological interactions for evolutionary responses to environmental changes is to large extent unknown. Here it is shown that interspecific competition may slow down rates of adaptation substantially and fundamentally change patterns of adaptation to long-term environmental changes. In the model investigated here, species compete for resources distributed along an ecological niche space. Environmental change is represented by a slowly moving resource maximum and evolutionary responses of single species are compared with responses of coalitions of two and three competing species. In scenarios with two and three species, species that are favored by increasing resource availability increase in equilibrium population size whereas disfavored species decline in size. Increased competition makes it less favorable for individuals of a disfavored species to occupy a niche close to the maximum and reduces the selection pressure for tracking the moving resource distribution. Individual-based simulations and an analysis using adaptive dynamics show that the combination of weaker selection pressure and reduced population size reduces the evolutionary rate of the disfavored species considerably. If the resource landscape moves stochastically, weak evolutionary responses cause large fluctuations in population size and thereby large extinction risk for competing species, whereas a single species subject to the same environmental variability may track the resource maximum closely and maintain a much more stable population size. Other studies have shown that competitive interactions may amplify changes in mean population sizes due to environmental changes and thereby increase extinction risks. This study accentuates the harmful role of competitive interactions by illustrating that they may also decrease rates of adaptation. The slowdown in evolutionary rates caused by competition may also contribute to explain low rates of morphological change in spite of large environmental fluctuations found in fossil records.
生态相互作用对于环境变化的进化响应的作用和重要性在很大程度上尚不清楚。本文表明，种间竞争可能会大幅减缓适应速度，并从根本上改变对长期环境变化的适应模式。在此研究的模型中，物种竞争沿生态位空间分布的资源。环境变化由缓慢移动的资源最大值表示，并将单个物种的进化响应与两个和三个竞争物种联盟的响应进行比较。在有两个和三个物种的情景中，受资源可利用性增加青睐的物种在平衡种群大小上增加，而不受青睐的物种大小下降。竞争加剧使得不受青睐物种的个体占据接近最大值的生态位变得不那么有利，并降低了跟踪移动资源分布的选择压力。基于个体的模拟和使用适应性动力学的分析表明，较弱的选择压力和种群大小减少的组合大大降低了不受青睐物种的进化速度。如果资源景观随机移动，微弱的进化响应会导致种群大小的大幅波动，从而使竞争物种面临较大的灭绝风险，而遭受相同环境变化的单个物种可能会紧密跟踪资源最大值并维持更稳定的种群大小。其他研究表明，竞争相互作用可能会放大由于环境变化导致的平均种群大小变化，从而增加灭绝风险。本研究通过说明竞争相互作用也可能降低适应速度，突出了其有害作用。竞争导致的进化速度放缓也可能有助于解释尽管在化石记录中发现了较大的环境波动，但形态变化速度却很低的现象。
