Functional Trait Variation within and Across Woody Plant Species Along an Elevation Gradient

Abstract

Plant phenotypes are defined by a set of traits that have been theorized to be closely linked to the fitness of individuals. These traits have an impact on their ability to grow and compete given the local environment. Variability (intra-specific or inter-specific) in the values of these functional traits is thought to be associated with the ability of an individual to survive in highly variable environments or a wide range of environments. Elevation gradients represent a change in environmental factors within a short spatial scale and hence offers the ideal context to examine functional trait variation. This study seeks to understand the extent of intraspecific trait variation and theorize the drivers of this variation in five woody plant species in response to a change in elevation in a tropical evergreen forest. I focused on three different functional traits i.e Specific leaf area (SLA), leaf dry matter content (LDMC), and Stem specific density (SSD) which represent leaf resource acquisition as wells as stem differentiation. When examining the trends of functional trait values for the entire data set irrespective of species identity, it was seen that differences in mean trait values drove the across-species trends. This highlights the role of the environment in selecting for species with specific mean trait values. Contrary to this, intra-specific trait values did not show directional selection in response to elevation, however, the percentage of the total variation associated with the intra-specific scale was significant. This indicates the occurrence of simultaneous counter gradients which may be leading to there being a lack of signal in functional trait values in response to elevation. I failed to establish a correlation between intra-specific trait variation and the elevation range of occurrence. The results highlight the high functional trait variation seen at the intra-specific scale and emphasizes the importance of considering intra-specific trait variation especially at the scales of high environmental heterogeneity.