Effects of community richness and competitive asymmetry on protozoa evolution in Sarracenia purpurea leaves

Predicting evolution in natural systems will require understanding how selection operates in multispecies communities. We predicted that the amount that traits evolve in multispecies mixtures would be less than the amount that would be predicted from the additive contributions of the pair-wise interactions and that subordinate species will be more likely to evolve in competitive systems than dominant species. We conducted an experimental test of these predictions using a guild of protozoans found in the water-filled leaves of the pitcher plant Sarracenia purpurea. The response to selection did not significantly change as we increased richness from monocultures to two- and four-species mixtures. In accordance with our second prediction, subordinate species demonstrated greater growth in competition after selection than before, while dominant species generally showed no response to selection. Monod-type experiments to determine minimum resource levels found that the dominant species had m...

预测自然系统中的进化需要理解选择作用在多物种群落（multispecies communities）中的运作方式。我们推测，多物种混合体系中性状的进化量将小于基于两两相互作用（pair-wise interactions）累加贡献所预测的量，且在竞争系统里，从属物种（subordinate species）比优势物种（dominant species）更易发生进化。我们利用紫瓶子草（Sarracenia purpurea）积水叶片中发现的原生动物（protozoans）类群，对这些推测开展了实验验证。当群落丰富度从单培养（monocultures）提升至两物种及四物种混合体系时，选择响应未发生显著变化。与第二项推测一致，从属物种在选择后的竞争环境中表现出比选择前更显著的生长，而优势物种通常无选择响应。用于测定最低资源水平的莫诺德型实验（Monod-type experiments）发现，优势物种具有m...