Patterns of relative abundance for tropical trees have been of interest since the expeditions of Alfred Russel Wallace, but we still have little understanding of how such patterns may be related to reproductive strategies. The coexistence of tree species in biodiverse communities is thought to be maintained to a large extent by density-dependent negative feedbacks at the seedling stage, however, when it comes to pollination, the case could be quite the opposite, with rare species suffering Allee effects, or reduced fitness due to the difficulty of finding a mate at low densities. Yet, to understand this, we must consider “functional abundance”, or the number of flowering individuals in the population, which may be lower than total adult abundance. Patterns of functional abundance may reduce abundance extremes between species during reproduction, and will determine the density and distance between flowering individuals, factors known to influence pollination success. We collected phenophase data for twenty-two tree species during the peak flowering season of 2016 in the 50 ha Korup Forest Dynamics Plot in Cameroon and asked how occurrence and location of individual reproductive events were related to local adult abundance patterns in the community, using nearest neighbor spatial statistics and linear regressions.
Results/Conclusions
The number of co-flowering individuals was significantly negatively correlated with total adult abundance, both at the family level and overall, with abundant species having a smaller proportion of flowering individuals. Species nearest-neighbor spatial patterns were more aggregated than random for both total adults and flowering individuals, however nearest neighbor distances of flowering individuals were increased relative to nearest neighbor distances of total adults, particularly for more abundant species. These results demonstrate that intraspecific patterns of flowering phenology in tropical forests are important to consider because they may affect the pollination landscape by functionally lowering the abundance of common species. This could level the playing field somewhat between rare and abundant species by lowering fitness costs for rarer species due to interspecific competition for pollinators, while at the same time lowering fitness costs for common species due to intraspecific competition for pollinators. In addition, if flowering ability is resource-dependent and rarer species benefit from low intraspecific competition for abiotic resources, this may explain the higher proportion of individuals of rare species flowering. Thus, the “rare species advantage” may in fact allow such species to maximize the size of their mate pool, and help them cope with pollination despite their low numbers.