The Unknown Life of Floaters: The Hidden Face of Sexual Selection

Abstract

Summary. Sexual selection, as a form of social selection based on reproductive resources, is a crucial driver of evolutionary change. Many studies on sexual selection identify potential targets only within the reproductive fraction of populations. Floaters constitute the non-territorial fraction of the population, according to the usual definitions. Floaters have been identified through exhaustive capture and marking programmes, removal and nest-box addition experiments, extra-pair paternity studies, acoustic marking and genetic studies. The literature shows that floaters may represent a considerable fraction of populations, especially among males. There is no clear evidence that size, condition or testosterone level is necessary for explaining floater status generally. However, the literature suggests that ornament size and expression are involved in territorial exclusion and may be either its cause or one of its consequences. There is some evidence that floaters survive and reproduce less well than terr...