Mixed mating system and spatial structure assure high reproductive rate of an endangered and endemic cactus

Demographic and spatial patterns are crucial traits in plant population dynamics. Associated with reproductive and pollination systems, these ecological parameters could promote adequate fruit and seed set and ensure population survival. Here, we described population and reproductive parameters of Parodia crassigibba , a threatened and endemic cactus species of the Brazilian Pampa. We described the spatial pattern, the size distribution and reproductive effort during a year of study. Through linear models, we compared fruit set and seed production to verify the reproductive systems and tested a potential correlation between spatial relationship between the distances among individuals and seed production. The population studied had a normal distribution of size classes with a positive relationship between plant size and their reproductive effort (number of flowers per individual). With an annual flowering pattern and a single peak of flowering, seven bee species were found visiting the flowers of P. crassigibba . These visitors contributed to pollination, but also self-compatibility with spontaneous self-pollination was observed. No pollen limitation occurred in the studied population. We found a significant negative relationship between distances among cacti individuals and seed production; indicating reproductive advantages to clumped individuals. Although we did not observe reproductive failure in threatened P. crassigibba, its population showed low recruitment. The endangered conservation status of this cactus species could be associated with other ecological processes; for example, low dispersal capability and recruitment contrasting with effective bee-pollination service ensuring fruit set and seed production.