Document: KEL-3-39-20

Investigations in relative abundance: a comparison of size distributions of co-occurring, congeneric Mexican trees.

KELLY, C.K.*

Dept. of Zoology, University of Oxford, Oxford OX1 3PS, UK ¹

Abstract:
Population size distributions were examined for twelve species of trees co-occurring at Chamela Biological Station in Jalisco, Mxico. Species had been selected as congeneric pairs and trios similar in gross morphology and ecology in order to better infer generalisations regarding correlates of relative abundance. When compared to expected exponential distributions based on population mean stem diameter, less abundant species were found to have more irregular distributions of individuals among size classes than more abundant species (6 of 6 possible contrasts). Given the agreement with the expectation of the theory of natural selection that more abundant species will be 'better adapted' to local conditions than less abundant species, the results indicate that extraneous confounding factors had been sufficiently minimized to reveal demographic differences correlated with relative abundance. It is suggested that temporal variation in reproductive success is the proximate cause for observed lower abundances, as it is for the greater irregularity in size distributions with which lower abundance is associated. The relationship between relative rarity and irregularity of size distributions was consistent whether within-contrast pairs were central or marginal in their geographic distributions, or a mixture of the two.

Keywords: commonness and rarity; sporadic recruitment; regeneration niche; phylogenetically independent contrasts

This abstract is being presented at: 2:00 PM in session:
Oral Session #16: Plant Demography: Trees and Shrubs.