Species Size and Reproductive Economy in Herbaceous Vegetation

Abstract

According to traditional theory, larger plants generaly have an advantage with respect to competition, especially for light. It seems a paradox then that most species that coexist within natural vegetation are relatively small; specis size distributions are right-skewed at virtually every scale. The critical question then becomes: if bigger is better in competition for resources, why then are there so many small plants? A potential explanation for this paradox is that smaller species may have greater reproductive economy-i.e. the ability to reproduce despite suppression from intense competition. Selection for greater reproductive economy may be associated with smaller seed sizes, increased rates of self-fertilization and/or clonality, and in the case of this study, smaller size at reproductive maturity. Random plots in an old field at Queen's University Biological Station were sampled and the largest and smallest reproductive individuals of each species were collected, dried and weighed - to test the hypothesis that smaller species can reproduce at a smaller proportion of their maximum potential plant sizes. The results did not support this, but the hypothesis that smaller plants have greater reproductive economy could not be rejected as it was not possible to record data for the largest possible plant size for each species (since even the largest plants were subjected to competition from neighbours). This provides a focus for future research. Understanding the role of plant size in affecting the process of species assembly has important implications for species coexistence and mechanisms of biodiversity preservation, and thus efforts involving conservation and ecosystem management.