Gragnani Alessandra, Scheffer Marten, Rinaldi Sergio
Am Nat. 1999 Jan;153(1):59-72. doi: 10.1086/303146.
Field patterns and experimental results suggest that the effect of zooplankton grazing on the abundance of large colonial cyanobacteria may differ strongly from case to case. In this article we present an extensive analysis of a model that describes the competition between cyanobacteria of the Oscillatoria group and green algae exploited by Daphnia. In particular, we study the response of the model to changes in the nutrient concentration and predation by zooplanktivorous fish. The analysis is repeated for an array of different assumptions on the nutritional value of cyanobacteria and selectivity of zooplankton grazing. When fish predation pressure is so high that Daphnia density is negligible, there is competitive exclusion between the two primary producers, and over a range of nutrient levels, there are two alternative attractors: one with only cyanobacteria and one with only green algae. When fish predation pressure is lower, zooplankton becomes important, and if grazing by these animals is sufficiently selective, this may cause a third attractor on which Daphnia, cyanobacteria, and algae coexist. This "mixed" attractor may be stationary, oscillatory, or chaotic. Depending on the nutrient level, the nutritional value of cyanobacteria, and the selectivity of zooplankton, cyanobacterial dominance may be either induced or eliminated in response to reduced fish predation. This is well in line with the confusing array of field studies and experimental results.
野外模式和实验结果表明，浮游动物捕食对大型群体蓝藻数量的影响可能因情况而异。在本文中，我们对一个描述颤藻属蓝藻与水蚤所捕食的绿藻之间竞争关系的模型进行了全面分析。具体而言，我们研究了该模型对营养物浓度变化以及浮游食性鱼类捕食的响应。针对蓝藻营养价值和浮游动物捕食选择性的一系列不同假设，我们重复进行了分析。当鱼类捕食压力很高以至于水蚤密度可忽略不计时，两种初级生产者之间存在竞争排斥，并且在一定营养水平范围内，存在两种替代吸引子：一种只有蓝藻，另一种只有绿藻。当鱼类捕食压力较低时，浮游动物变得重要起来，如果这些动物的捕食具有足够的选择性，这可能会导致出现第三种吸引子，即水蚤、蓝藻和藻类共存。这种“混合”吸引子可能是稳定的、振荡的或混沌的。根据营养水平、蓝藻的营养价值以及浮游动物的选择性，蓝藻优势可能会因鱼类捕食减少而被诱导产生或消除。这与一系列令人困惑的野外研究和实验结果非常吻合。
