Geographic variation in demography of a temperate reef snail: importance of multiple life-history traits

Individual- and population-level performance may reflect trade-offs between energy allocation to different key demographic processes, such as growth and reproduction, which can, in turn, be influenced by local biotic and abiotic conditions. We explored geographic variation in demographic rates of an exploited benthic species, the wavy-turban snail Megastraea undosa, along the Pacific coast of Baja California, Mexico. We compared key life-history traits (i.e. fecundity, size at maturity, growth, and survivorship) of populations existing between 20 and 170 km apart under different conditions of ocean temperature and food availability. Trade-offs between growth and reproduction were evident across this environmental gradient, with higher growth rates in warmer locations leading to lower size-specific investment in gonad production. Because later onset of reproduction in populations from warmer areas was compensated by greater fecundity at larger sizes, geographic variation in life-history strategies resulted in similar age-specific reproductive output among different populations. However, we observed that, while there is substantial variation in demographic rates of the study species, harvest management is applied uniformly, and this results in southern populations achieving lower reproductive output before they reach a legally harvestable size. Our results highlight the importance of considering geographic variation in multiple life-history traits when managing across a mosaic of land-and seascapes characterized by varying environmental conditions.