OOS 18-4 - Importance of intraspecific variability in morphological trait space for community assembly of hawkmoths along a broad tropical elevational gradient

Ecological processes which govern community assembly may be separated into two categories, those causing either a convergence or a divergence of functional traits of species co-occurring in a community. Several metrics of functional (trait) diversity have been used to characterize the distribution of traits in a community and the importance of incorporating intraspecific trait variability (ITV) into such studies has been increasingly recognized over the last decade.

We measured the morphological traits of body-mass, wing-loading, and wing aspect-ratio of 3,301 free-ranging individuals of 76 hawkmoth species without having to collect or even constrain them. We investigated convergence and divergence in their morphospace at 13 elevations along a 2.6km transect in the eastern Himalayas, a little studied biodiversity hotspot of global importance. We used these trait measurements and T-statistic metrics to assess the strength of intra-community (“internal") and extra-community (“external”) filters which determine the composition of communities vis-a-vis the regional pool of species.

The trait distribution of constituent species turned out to be non-random subsets of the community trait distribution, providing strong evidence for internal filtering in all elevational communities. On average, a species occupied as much as 50-75% of the total community trait space; yet the T-statistic metric for internal filter was sufficiently sensitive to detect a strong non-random structure in the trait distribution.

We suggest that the change of T-statistic metrics along the environmental gradient may provide more clues to the process of community assembly than previously envisaged. A large, smoothly varying and well sampled environmental span would make it easier to discern them. Developing T-statistics for combined analysis of multiple traits will perhaps provide a more accurate picture of internal/filtering and niche complementarity. Moths are a hyper-diverse taxon and a very important component of many ecosystems. Our technique for accurately measuring body and wing dimensions of free-ranging moths can generate trait database for a large number of individuals in a time- and resource-efficient manner for a variety of community assembly studies.