Intraspecific trait variation affects the spatial patterns of functional diversity among moorland plant communities

Background/Question/Methods

Understanding the spatial patterns of functional diversity is critical for both explaining community assembly processes and conservation planning. Although recent studies suggested that intraspecific trait variation might influence community structure, previous studies of the spatial patterns of functional diversity focused exclusively on species mean traits. We studied species composition and three functional traits (leaf height, leaf mass per unit area (LMA), and individual leaf size) in vascular plant communities at 27 moorland sites that are widely interspersed within the subalpine zone of northern Japan. The moorland sites are variably isolated from each other within an inhospitable matrix (i.e., forests). Alpine and subalpine moorland ecosystems contain unique communities, often with a large number of endemic and threatened species. These ecosystems are considered to be vulnerable to environmental change, and especially to global warming. First, we examined how trait variance is partitioned across and within species. Second, we investigated how incorporating intraspecific variation changed the spatial patterns of functional diversity and whether incorporating intraspecific variation improves the detection of community assembly processes that operate at multiple spatial scales.

Results/Conclusions

Interspecific differences accounted for 81% of the total variance of leaf height, 82% of that of LMA, and 89% of that of leaf size. Although the amount of intraspecific variation was considerably less than that of interspecific variation, we found that intraspecific variation contributed to increased between-site functional diversity and decreased within-transect functional diversity. This result supported environmental filtering that beta functional diversity increases because plants show intraspecific variation along environmental gradients, resulting in larger functional turnover among communities. In addition, incorporating intraspecific variation improved the detection of environmental filtering processes operating at multiple scales. Thus, intraspecific variation plays important roles in species coexistence at multiple scales. Our results also suggested that researchers and managers need to be careful about the underestimation of beta functional diversity obtained from species mean traits when planning effective strategies to conserve regional functional diversity.