Mathematical ecology on persistence of cross predation in fish communities

在几种鱼类中发现了两种形态类型(“右”和“左”)，被称为反对称的典型例子。有人认为，第一，这种二相性(称为侧向性)是可遗传的；第二，每一物种的侧向性频率在0.5左右波动；第三，捕食者主要利用相反侧向性的猎物；即左撇子和右撇子捕食分别以右手和左手为食的猎物。后者被定义为“交叉捕食”；反义词“平行捕食”指的是在同一侧向内的捕食。我们假设，交叉捕食驱动了两种形态类型之间生存和繁殖优势的交替，导致了维持二型性的频率依赖选择。为此，我们建立了一个捕食者/一个捕食者系统和具有杂食性的三营养级系统的种群动力学数学模型。数学分析和计算机模拟很好地解释了自然界中横向频率的行为，就交叉捕食主导平行捕食而言。此外，模拟表明，当一个物种中只存在一种形态类型时，另一种类型可以入侵。这表明，在所有相互作用的物种中都保持着二形性。

Two morphological types ("righty" and "lefty") have been discovered in several fish species and are referred to as a typical example of antisymmetry. It has been suggested, first, that this dimorphism (called laterality) is inheritable ; second, that the frequencies of laterality in each species fluctuate around 0.5 ; and third, that predators mainly exploit prey of the opposite laterality ; that is, lefty and righty predators prey on righties and lefties, respectively. The latter is defined as "cross predation" ; the antonym "parallel predation" means predation within the same laterality. We hypothesized that cross predation drives alternation of the survival and reproductive advantages between two morphological types, leading to frequency-dependent selection that maintains the dimorphism. To investigate this, we constructed mathematical models of population dynamics of one prey/one predator systems and three-trophic-level systems with omnivory. Mathematical analysis and computer simulations explained the behavior of the laterality frequency in nature well, insofar as cross predation dominated over parallel predation. Furthermore, the simulations showed that when only one of the morphological types exists in a species, the other type can invade. This suggests that dimorphism is maintained in all interacting species.