Phenotypic natural selection on flower biomass allocation in the tropical treeIpomoea wolcottiana Rose (Convolvulaceae)

Intra-population patterns of phenotypic variation in biomass allocation to flower parts are analyzed for the treeIpomoea wolcottiana, and the effects of this variation on fruit production are evaluated in two consecutive years. Significant variation among individuals was found for biomass of both sexual and attractive structures. Repeatability values showed that variation in these structures could be heritable. Analyses of phenotypic natural selection indicated a positive directional selection for both, gynoecium and petals mass in both years. These results suggest that floral resource allocation can be modified by phenotypic natural selection. To our knowledge this is the first paper that reports phenotypic natural selection in floral characteristics of a tropical tree species.     

Effects of seasonal rainfall on radial growth in two tropical tree species

 Seasonal drought may limit primary productivity in most of the tropics, but the determinants of tree growth are not well known. A 10-year study of the deciduous trees Cochlospermum vitifolium (Willd.) Spreng. (Cochlospermaceae) and Cnidoscolus spinosus Lundell (Euphorbiaceae) in southwestern México showed radial growth to be highly correlated (both r>0.85) only with precipitation during an interval of <2 months in the mid-wet season. Growth was not affected by total annual precipitation or by an early starting or late ending of the wet season, or by heavy rainfall in the dry season. Annual mean girth increments ranged from 0.03 to 3.31 cm and −0.1 to 2.01 cm, respectively. The best model for growth (r ²>0.85) was a linear combination of mid-summer precipitation (positive coefficient) and total precipitation over the previous 2 years (negative coefficient). Comparison with other species showed heterogeneous responses of wood production to climate variation, and suggests that the range of functional types of dry forest trees is still unknown. Received: 9 September 1996 / Accepted: 4 March 1997