COS 87-2 - Does functional trait-based ecology explain community assembly? A case of mass flowering sky-islands of northern Western Ghats

Background/Question/Methods

The pursuit for principles that explain species assemblages within a community has always been the central focus of plant community ecologists. Previous attempts identify biotic interactions and environmental (abiotic) filtering as drivers of community assembly. Given that annually flowering grassland communities are already bound to a short window of favorable environmental conditions, we took a functional trait-based approach to understand community assembly. Laterite outcrops that form ‘sky-islands’ in the northern Western Ghats (NWG), host extravagant displays of short-lived mass flowering herbaceous species. Focusing on key pollination-related functional traits such as floral displays (color and abundance), flowering phenology, and pollinator visitation frequency, we asked,

1. 
   Do species show convergent or divergent floral color distribution in their flowering phenology?
   
   


2. 
   Do pollinators prefer the most abundant floral color?
   
   

Four sky-island communities of NWG were studied where phenology census was taken thrice a month by counting the number of individuals in flowering phenophase using fixed transects. Seasonal changes in pollinator activity were captured using natural pollinator observations at equal intervals. Spectral reflectance of floral parts, floral shape and size were quantified in the field for all flowering species. Later, bipartite pollination networks were built and analyzed using the bipartite package in R.

Results/Conclusions

We observed distinct floral color-based phenology structuring in our study sites where similarly-colored flowering species tend to synchronize their flowering time with each other. We also found that as the most abundant floral color group shifted from one to the other, major pollinator groups show variation in their visitations. Three native Apis spp. dominated the pollination landscape in all sites as they provide the majority of the floral visits. In the pollination networks, they were also found to be the most generalist pollinators as they visited the highest number of flowering species. Consequently, bees are crucial in maintaining the community stability of these unique habitats. We found that the pollinators prefer the most abundant floral color group except for the white-colored species as the bees did not prefer them even when white flowering species were mass flowering.

Our results suggest that all our study communities experience similar environmental conditions, yet flowering species' composition and distribution do not resonate with expected similarity. These differences in species assemblages are the result of varying functional traits that directly influence both plant-plant as well as plant-pollinator interactions.