Closely related species (e.g., sister species) often show microallopatry, a pattern known as phylogenetic overdispersion. The manifestation of phylogenetic overdispersion at small phylogenetic and spatial scales suggests antagonistic interspecific interactions that dominate only among closely related species. Reproductive interference (costly interspecific mating interactions) is one of the likely processes that underlie phylogenetic overdispersion. Here I overview two case studies of reproductive interference (the first is about its cause, and the second is about its consequence). First, between a pair of congeneric seed beetle species, genital morphology, which should evolve primarily due to within-species sexual selection, mediates the cost of interspecific mating (i.e., the strength of reproductive interference). Second, a simulation model shows that habitat segregation that evolves to avoid reproductive interference stabilizes the coexistence of ecologically similar species (conspecific aggregation intensifies intraspecific resource competition). These studies illustrate how low-level processes (sensu Vellend 2016) map to high-level processes. They also imply how demographic parameters evolve.