Intraspecific Trait Variability Determines Understorey Plant Community Assembly

Abstract Increasing evidence points to the major impact of intraspecific variability in species characteristics on community assembly. Contrasting theories predict that high trait variability might either steepening dominance orders or promote diversity. Here, we try to test these predictions with understorey plants in a Polish mixed temperate forest. We focus on four important traits (leaf dry mass LDW, plant height SH, specific leaf area SLA, and number of flowers NF) of the small balsam Impatiens parviflora, the dominant species in this forest system. We relate trait variability to community species richness and abundances, as well as to soil characteristics. The variance – mean relationships of LDW, LH, and NF, but not of SLA, closely followed power functions with slopes > 1.5. Contrary to theory, abundances but not species richness of non-I. parviflora species significantly decreased within increasing variance in I. parviflora trait expression. High trait variability prevailed a higher species richness. Trait variability did not significantly influence species composition and was not significantly correlated with soil characteristics. Our results emphasis the need to study trait variability in terms of appropriate statistical standards as provided by the allometric variance - mean relationship. We argue that an individual based study of local trait variability might return important insights into the composition and assembly of local communities.