Predator-predator interactions, or “multiple predator effects” (MPEs), are pervasive in the structuring of communities and complicate predictive quantifications of ecosystem dynamics. The nature of MPEs is also context-dependent, manifesting differently among species, prey densities and habitat structures. However, there has hitherto been a lack of consideration for the implications of intraspecific demographic variation within populations for the strength of MPEs. The present study extends MPE concepts to examine intraspecific interactions among male and female predators across differences in prey densities using a functional response approach. Focusing on a copepod-mosquito model predator-prey system, interaction strengths of different sex ratio pairs of Lovenula raynerae were quantified towards larval Culex pipiens complex prey, with observations compared to both additive and substitutive model predictions. Copepods exhibited destabilising Type II functional responses in all treatments, with female copepods significantly more voracious than males under multiple predator groups. Lovenula raynerae exhibited significantly negative MPEs overall which resulted in prey risk reductions. However, whilst not statistically clear, the magnitude of antagonistic interactions subtly differed among predator-predator compositions and prey densities, with female-female antagonisms generally prevalent at low prey densities, and male-male negative interactions greater under high prey densities. Mixed-sex copepod group predation was predicted by both additive and substitutive models, and additive models generated significantly higher consumption estimates than substitutive equivalents given that their predictions were based on the absence of antagonistic non-trophic interactions. We propose the importance of internal population sex demographics as a further context-dependency which influences the nature of MPEs, with demographic implications requiring investigation across other taxonomic and trophic groups.

中文翻译：

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在不断变化的捕食者性别比例中检查种内多重捕食者的影响

捕食者-捕食者相互作用，或“多重捕食者效应”（MPE），在群落结构中普遍存在，并使生态系统动态的预测量化复杂化。MPE 的性质也取决于环境，在物种、猎物密度和栖息地结构之间表现不同。然而，迄今为止，一直缺乏考虑种群内种内人口变异对 MPE 强度的影响。本研究扩展了 MPE 概念，以使用功能反应方法检查雄性和雌性捕食者之间在猎物密度差异中的种内相互作用。以桡足类-蚊子模型捕食者-猎物系统为重点，量化了不同性别比例的Lovenula raynerae对幼虫Culex pipiens复合猎物的相互作用强度，将观察结果与加法和替代模型预测进行比较。桡足类在所有处理中都表现出不稳定的 II 型功能反应，在多个捕食者群体下，雌性桡足类动物明显比雄性更贪婪。Lovenula raynerae 总体上表现出显着的负 MPE，这导致猎物风险降低。然而，虽然在统计上并不明确，但捕食者-捕食者组成和猎物密度之间的拮抗相互作用的程度略有不同，雌性-雌性对抗通常在低猎物密度下普遍存在，而在高猎物密度下雄性-雄性负面相互作用更大。混合性桡足类群捕食通过加法和替代模型进行预测，考虑到它们的预测是基于不存在对抗性非营养相互作用的，加法模型产生了比替代等效模型更高的消耗估计值。我们提出内部人口性别人口统计作为影响 MPE 性质的进一步背景依赖性的重要性，其人口影响需要对其他分类和营养群体进行调查。