Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States of America.
School of Marine Sciences, University of Maine, Orono, ME, United States of America.
PLoS One. 2022 Sep 16;17(9):e0274183. doi: 10.1371/journal.pone.0274183. eCollection 2022.
Under most natural marine conditions, phytoplankton cells suspended in the water column are too distantly spaced for direct competition for resources (i.e., overlapping cell boundary layers) to be a routine occurrence. Accordingly, resource-based competitive exclusion should be rare. In contrast, contemporary ecosystem models typically predict an exclusion of larger phytoplankton size classes under low-nutrient conditions, an outcome interpreted as reflecting the competitive advantage of small cells having much higher nutrient 'affinities' than larger cells. Here, we develop mechanistically-focused expressions for steady-state, nutrient-limited phytoplankton growth that are consistent with the discrete, distantly-spaced cells of natural populations. These expressions, when encompassed in a phytoplankton-zooplankton model, yield sustained diversity across all size classes over the full range in nutrient concentrations observed in the ocean. In other words, our model does not exhibit resource-based competitive exclusion between size classes previously associated with size-dependent differences in nutrient 'affinities'.
在大多数自然海洋条件下，悬浮在水柱中的浮游植物细胞之间的距离太远，以至于资源的直接竞争（即细胞边界层重叠）不太可能经常发生。因此，基于资源的竞争排斥应该很少见。相比之下，当代生态系统模型通常预测在低营养条件下较大的浮游植物类群被排斥，这种结果被解释为反映了小细胞具有比大细胞更高的营养“亲和力”的竞争优势。在这里，我们为稳态、受营养限制的浮游植物生长开发了以机制为重点的表达方法，这些表达方法与自然种群中离散、远距离间隔的细胞一致。当这些表达式包含在浮游植物-浮游动物模型中时，在海洋中观察到的所有营养浓度范围内，所有大小类别的多样性都能持续存在。换句话说，我们的模型没有表现出以前与营养“亲和力”的大小依赖性差异相关的大小类之间基于资源的竞争排斥。
