Plants are least suppressed by their frequent neighbours: the relationship between competitive ability and spatial aggregation patterns

Summary Previous studies have concluded that spatial aggregation of conspecifics should benefit weak competitors and put stronger competitors at a disadvantage, thus promoting plant species coexistence. However, if competitive ability is viewed as a behavioural trait, it becomes evident that traits determining spatial patterns and competitive ability could co‐evolve, resulting in greater dispersal in stronger competitors and reduced competitive ability in spatially aggregated species. To test this prediction, we combined spatial data from a field survey of seven temperate grassland communities with the results of a common‐garden competition experiment involving 28 focal species. We found that species exhibiting strong conspecific aggregation and infrequent heterospecific encounters in the field maintained greater growth in competition with conspecifics than with heterospecifics. In contrast, species that mostly encountered heterospecific neighbours in the field achieved greater growth when surrounded by heterospecific than conspecific neighbours, indicating greater competitive ability. The observed patterns of conspecific aggregation were related to variation in clonal dispersal characteristics and there was a direct positive relationship between clonal dispersal distance and competitive ability. Synthesis . Our study demonstrates that viewing competitive ability as a behavioural trait that imposes different costs and benefits on an individual depending on the identity of its neighbours can provide new insights into the long‐debated topic of mechanisms promoting plant species coexistence.