Investigations in commonness and rarity: a comparative analysis of co-occurring, congeneric Mexican trees

Population size distributions were examined for 12 species of trees co-occu rring at Chamela Biological Station in Jalisco, Mexico. Species had been se lected as congeneric pairs and trios similar in gross morphology and ecolog y in order better to identify correlates of relative abundance. Rarer speci es were found unanimously to have more irregular distributions of individua ls among size classes than more common species when distributions were comp ared to a smooth, descending curve constructed from population mean stem di ameters (an exponential distribution). Examination among species of pattern s of deviation from these corresponding smooth distributions indicates that the most reasonably inferred cause for the observed pattern is consistent differences in degree of fluctuation in recruitment into adult size classes . These results thereby suggest a demographic difference between locally ra rer and more common species that may be generally associated with observed differences in relative abundance and indicate a focus for management of ra rity in forest trees.