Population differences in female resource abundance, adult sex ratio, and male mating success in Dendrobates pumilio

In this study I examined the relationship among abundance of reproductive resources, population density, and adult sex ratio in the strawberry dart-poison frog, Dendrobates pumilio, and how these variables in turn influence the mating system, male reproductive success, and sexual selection. I studied the mating behavior in two populations of D. pumilio living in a primary and secondary rainforest on the Caribbean slope of Costa Rica. The abundance of tadpole-rearing sites (reproductive resources for females) was approximately 10-fold higher in the secondary forest. Accordingly, the population density was higher and the adult sex ratio was strongly female biased in the secondary forest, whereas the adult sex ratio was even in the primary forest. The female-biased sex ratio was associated with a higher level of polygyny and higher male mating and reproductive success in the secondary forest. In contrast, the level of polyandry did not differ between habitats. As expected, the opportunity for sexual selection on male mating success was lower in the secondary forest, the habitat with high female density. In conclusion, my results suggest that ecological variables such as resource availability have a great impact on the mating system and sexual selection through their effect on population structure. Moreover, the results of this study give further evidence that the opportunity for sexual selection is influenced by the adult sex ratio and hence by the operational sex ratio in a population. Copyright 2002.