Kappeler’s framework for animal social systems and its impact on behavioral ecology and sociobiology

Peter Kappeler’s seminal work on animal social systems has built a strong conceptual foundation for generations of researchers (Kappeler (2019) Behav Ecol Sociobiol 73:13). The most notable and important contribution of his work has been a clear framework for animal social systems, clarifying the muddling of definitions. Unfortunately, many have used flawed definitions in their research on social systems, or even worse, no definitions at all. In contrast, Kappeler`s framework emphasizes that there are four inter-related components of the social system: (i) social organization, (ii) social structure, (iii) mating system, and (iv) care system. The framework is powerful for numerous reasons. Most importantly, these clearly defined components promote empirical and comparative research that does not confuse or confound behaviours coming under different forms of selection. Moreover, the framework permits the study of how these components are interconnected, instead of taking mixed definitions as an a priori. It allows for the identification of > 1000 types of social systems. Even so, the framework has not solved all challenges, most notably how to quantify social structure, which is arguably, the most complex social system component. Despite this limitation, the framework has enormous potential to shape our understanding of social diversity across a broad range of taxa. This Topical Collection advocates for the greater use of the framework in behavioural ecology and sociobiology while allowing for space to critically address its limitations. For decades, a major effort of behavioral ecology and sociobiology research has been to explain the remarkable diversity in animal social systems. As an introduction to a Topical Collection on animal social systems, we emphasize the impact of Peter Kappeler’s (2019); this journal) framework and advocate for its application to a wide range of taxa. Kappeler’s framework is powerful because it relies on clear definitions that allow for clear quantitative assessments and the identification of thousands of animal social systems. By facilitating discussion on how Kappeler’s framework has advanced our understanding and compares to other frameworks, this Topical Collection will help us move towards an unifying framework.