An interaction mechanism for the maintenance of fission-fusion dynamics under different individual densities
An interaction mechanism for the maintenance of fission-fusion dynamics under different individual densities
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DOI：
10.7717/peerj.8974
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发表时间：
2020-05-14
期刊：
影响因子：
2.7
通讯作者：
Krause, Jens
中科院分区：
文献类型：
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作者：
Bierbach, David;Krause, Stefan;Krause, Jens
尽管面临着不断变化的环境条件，动物的社会组织往往表现出高度的一致性。特别是在鱼群中，人们发现，即使密度发生变化，描述个体独处或群居时期的裂变融合动力学也保持不变。这种补偿能力被认为是对持续捕食压力的适应，但个体能够主动补偿密度变化的机制尚不清楚。当前研究的目的是确定能够实现这种主动补偿的行为模式。我们比较了两种生活在邻近栖息地的大西洋莫莉（Poecilia mexicana）的裂变融合动力学，它们生活在非常不同的捕食者制度中：栖息在硫酸盐洞穴内低捕食环境中的洞穴莫莉（Belostoma sp.），以及直接生活在洞穴外的高捕食环境中的“表面”莫莉（以后称为“表面”莫莉）。我们分析了它们在每0.36米12条和6条鱼两种不同鱼密度下的裂变融合动力学(2)。正如预期的那样，水面摩利鱼比洞穴摩利鱼花更多的时间进行社交活动，而这种社交时间的差异是由于水面摩利鱼不太可能中断社交活动（一旦有了社交伙伴），而比洞穴摩利鱼更有可能恢复社交活动（一旦独处）。有趣的是，与洞穴里的摩利鱼相比，水面上的摩利鱼也不太可能在社会伙伴之间切换。随机漫步模拟预测，在低密度处理下，每个种群的社会接触都会减少。虽然洞栖moli很大程度上遵循了这一预测，但表面moli即使在低密度下也保持了它们的相互作用概率。当密度降低时，表面mollies通过减小由群体形成的凸多边形的尺寸来实现这一点。这可能使它们在很大程度上保持它们的裂变聚变动力学，同时仍然能够作为一个群体访问大部分可用区域。在低密度访问的区域也观察到轻微减少（21%），但不足以解释鱼类如何保持其裂变融合动力学。最后，我们讨论了可能导致多边形尺寸减小的潜在运动规则，并测试了它们的性能。
Animals often show high consistency in their social organisation despite facing changing environmental conditions. Especially in shoaling fish, fission-fusion dynamics that describe for which periods individuals are solitary or social have been found to remain unaltered even when density changed. This compensatory ability is assumed to be an adaptation towards constant predation pressure, but the mechanism through which individuals can actively compensate for density changes is yet unknown. The aim of the current study is to identify behavioural patterns that enable this active compensation. We compared the fission-fusion dynamics of two populations of the live-bearing Atlantic molly (Poecilia mexicana) that live in adjacent habitats with very different predator regimes: cave mollies that inhabit a low-predation environment inside a sulfidic cave with a low density of predatory water bugs (Belostoma sp.), and mollies that live directly outside the cave (henceforth called "surface" mollies) in a high-predation environment. We analysed their fission-fusion dynamics under two different fish densities of 12 and 6 fish per 0.36 m(2). As expected, surface mollies spent more time being social than cave mollies, and this difference in social time was a result of surface mollies being less likely to discontinue social contact (once they had a social partner) and being more likely to resume social contact (once alone) than cave mollies. Interestingly, surface mollies were also less likely to switch among social partners than cave mollies. A random walk simulation predicted each population to show reduced social encounters in the low density treatment. While cave mollies largely followed this prediction, surface mollies maintained their interaction probabilities even at low density. Surface mollies achieved this by a reduction in the size of a convex polygon formed by the group as density decreased. This may allow them to largely maintain their fission-fusion dynamics while still being able to visit large parts of the available area as a group. A slight reduction (21%) in the area visited at low densities was also observed but insufficient to explain how the fish maintained their fission-fusion dynamics. Finally, we discuss potential movement rules that could account for the reduction of polygon size and test their performance.