The role of Intraspecific trait variation in driving Species Distributions and habitat associations of tree seedlings

Abstract

We are witnessing unprecedented levels of human induced alteration of forest ecosystems. To devise conservation efforts for fragmented forests, it is imperative to identify the mechanisms by which ecological processes maintain diversity and ecosystem functions. Environmental Filtering is a key process that influences species at the early life stages and determines future community composition. My study examines how the context in which environmental filtering occurs, in terms of intraspecific variation in traits and environmental heterogeneity, determines the final observed patterns in the community. The study site, a 3600-ha landscape at Kadumane in the Western Ghats is a patchwork of tropical rainforest fragments separated by human structures and plantations. I sampled tree saplings from 149 (2mx2m) plots, across 6 forest fragments, and measured their leaf, stem, root and organismal traits along with the light (canopy openness photographs) and water (soil moisture sensor) conditions at each plot. My objectives were to (a) measure functional traits related to key organismal functions as per standard protocol; (b) quantify species-wise intraspecific trait variation(ISTV); (c) characterize niche width in terms of standard deviation, and functional positions as differences of species trait means from community trait mean; (d) relate the ISTV of species to their abundance, niche width and functional position through linear regression. I show through this study that intraspecific variation in leaf traits such as Leaf Dry Matter Content and Leaf Mass Fraction is correlated with higher abundance and a wider environmental niche. ISTV in stem and root bio mass allocation traits are correlated with lower niche widths and marginal functional positions in the community. Marginal functional position in Stem Mass fraction also correlates with a marginal niche position in the environment. These results together indicate that studying environmental filtering as just the interaction of the average phenotype of species with the mean environment is insufficient and the consideration of ISTV brings forth a more complete picture.