How protandry and protogyny affect female mating failure: a spatial population model

Abstract

Population growth and persistence depend on the collective ability of individuals to find mates in both space and time. When individuals are reproductively mature for only a portion of a population's breeding season, reproductive asynchrony can cause mating failure and a temporal Allee effect, which is exacerbated by spatial constraints in isolated populations. However, the effect of phenological variation by sex (protandry, protogyny) in spatiotemporal mate finding is not well understood. Here, we examine the interacting roles of sex-specific and population-wide individual asynchrony on female matelessness in spatially isolated populations. By incorporating sex-specific phenology into a two-sex reaction-diffusion system, we explore female matelessness as a function of phenology, movement behavior, and patch size. Although individual asynchrony may lead to female mating failure in small and isolated populations, we find that moderate protandry reduces female mating failure across a variety of scenarios. We go on to examine model behavior for a case study based on the bagworm, Thyridopteryx ephemeraeformis Haworth (Lepidoptera: Psychidae), where many populations exhibit pronounced protogyny. Overall, we find a consistent benefit of moderate protandry, which may mitigate female matelessness for many populations.