XVI International Botanical Congess

The abundance and leaf specific mass (g/m2 [LSM]) of three Vaccinium shrubs, similar in all respects except leaf morphology, were measured across an abiotic gradient in coastal British Columbia. Photon flux density and wind speeds decrease as soil moisture increases across transects extending from the shoreline into forested habitats. LSM varies intra specifically across transects, being highest at the shoreline and lowest in forested habitats, presumably in response to changing abiotic conditions. Variation in species' abundances parallels intraspecific morphological variation. The species with highest average LSM is most abundant at the shoreline, the species with the lowest LSM is most abundant in the forest interior, and that with intermediate LSM peaks at intermediate positions along transects. An investigation of these species on nearby islands show that this pattern is repeatable through space. These results suggest that intraspecific differences in LSM represent selective adjustments to local abiotic conditions and changes in the abundance of each species can be attributed to interspecific differences in LSM. Therefore, LSM both subdivides populations of each species and concurrently delineates interspecific niche space.