Can't live with them, can't live without them? Balancing mating and competition in two-sex populations

Two-sex populations are usually studied through frequency-dependent models that describe how sex ratio affects mating, recruitment, and population growth. However, in two-sex populations, mating and recruitment should also be affected by density and by its interactions with sex ratio. Density may have positive effects on mating (Allee effects) but negative effects on other demographic processes. In this study, we quantified how positive and negative inter-sexual interactions balance in two-sex populations. Using a dioecious grass (Poa arachnifera), we established experimental field populations that varied in density and sex ratio. We then quantified mating success (seed fertilization) and non-mating demographic performance, and integrated these responses to project population-level recruitment. Female mating success was positively density-dependent, especially at female-biased sex ratios. Other demographic processes were negatively density dependent and, in some cases, frequency depende...