Insights into the Factors Controlling the Distributions of the Narrow Endemic, Helenium virginicum and its Widespread Congener, H. autumnale, Through a Study of Their Relative Competitive Abilities and Growth Rates

Abstract

We undertook a growth and competition study of H. autumnale and H. virginicum to gain insight into the causes of their distributions. We used a multiple de Wit replacement series to study competition, run concurrently with a growth study to identify morphological and physiological characters that might explain competitive outcomes, as was done by Snyder et al. ( 1994 ). Our aims were to answer the following questions. 1.) Does H. virginicum have the characteristics of a stress tolerant plant, and does H. autumnale have the characteristics of a competitor plant? 2.) Does each species grow less well on the soil of its congener, than on its own soil, when raised in a common garden? 3.) Is the endemic plant a poorer competitor than its widespread congener? 4.) Does competition decrease with increasing nutrient stress? 5.) Does the endemic plant have a slower growth rate than its congener on a nutrient enriched soil? 6.) Do the patterns of resource allocation in the endemic and its widespread congener help explain their distributions? [From Introduction]