Cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii are two harmful species which co-occur and successively dominate in freshwaters globally. Within-species strain variability affects cyanobacterial population responses to environmental conditions, and it is unclear which species/strain would dominate under different environmental conditions. This study applied a Monte Carlo approach to a phytoplankton dynamic growth model to identify how growth variability of multiple strains of these two species affects their competition.

Pairwise competition between four M. aeruginosa and eight C. raciborskii strains was simulated using a deterministic model, parameterized with laboratory measurements of growth and light attenuation for all strains, and run at two temperatures and light intensities. 17 000 runs were simulated for each pair using a statistical distribution with Monte Carlo approach.

The model results showed that cyanobacterial competition was highly variable, depending on strains present, light and temperature conditions. There was no absolute ‘winner’ under all conditions as there were always strains predicted to coexist with the dominant strains, which were M. aeruginosa strains at 20 °C and C. raciborskii strains at 28 °C. The uncertainty in prediction of species competition outcomes was due to the substantial variability of growth responses within and between strains. Overall, this study demonstrates that within-species strain variability has a potentially large effect on cyanobacterial population dynamics, and therefore this variability may substantially reduce confidence in predicting outcomes of phytoplankton competition in deterministic models, that are based on only one set of parameters for each species or strain.

蓝藻铜绿微囊藻和拟柱raciborskii两种有害物种共同出现在全球淡水先后占据主导地位。种内菌株的变异性会影响蓝细菌种群对环境条件的反应，目前尚不清楚在不同环境条件下哪种菌种/菌株将占主导地位。这项研究将蒙特卡洛方法应用于浮游植物动态生长模型，以确定这两个物种的多个菌株的生长变异性如何影响它们的竞争。

使用确定性模型模拟了四个铜绿假单胞菌菌株和八个拉氏梭菌菌株之间的成对竞争，并通过实验室测量所有菌株的生长和光衰减进行参数化，并在两个温度和光强度下运行。使用蒙特卡洛方法进行统计分布，为每对模拟了17,000次跑步。

模型结果表明，蓝细菌竞争是高度可变的，取决于存在的菌株，光照和温度条件。在所有条件下都没有绝对的“赢家”，因为总会预测到与主要菌株共存的菌株，例如在20°C的铜绿假单胞菌菌株和拉氏梭菌。菌株在28°C时。物种竞争结果预测的不确定性是由于品系内部和品系之间生长反应的显着差异所致。总体而言，这项研究表明，种内菌株的变异性可能会对蓝藻种群动态产生较大影响，因此，这种变异性可能会大大降低在确定性模型中预测浮游植物竞争结果的信心，因为确定性模型仅基于一套参数物种或品系。