Competition and nutrient effects on the local distribution and abundance of Coreopsis lanceolata L. (Asteraceae)

Includes bibliographical references (pages [55]-62).The distribution of a species is determined by the interactions of life history strategies, stress, rarity, competition, resource availability, dispersal ability, and other factors. All species share three traits in common: geographic range, habitat specificity, and local abundance which determine a species’ form of rarity. The form of rarity can influence the manner in which a species responds to abiotic stresses and the life history strategy it adopts. Restricted locally abundant species are characterized by a broad geographic range, narrow habitat specificity, and local abundance. This form of distributional pattern results from a trade-off between stress- tolerance and competitive ability. In order to determine if a trade-off between stress-tolerance and competitive ability is responsible for the restricted, locally abundant species Coreopsis lanceolata L. (Asteraceae), two studies were carried out. The first study, a survey of the natural populations, quantified environmental parameters, morphological traits, and reproductive traits. The survey of natural populations indicated that these areas are stressful habitats characterized by low soil moisture and low nutrient availability. The second study was a transplant garden experiment in which three levels of nutrients and two levels of competition were manipulated. One garden was adjacent to a natural population and the second was in a more productive area where C. lanceolata did not occur. The results showed that plants were more successful, having greater growth, survivorship, and reproduction, in an area where C. lanceolata does not now occur if competitors were removed. Nutrient effects were transient and only affected growth soon after application. The fact that C. lanceolata is successful in its stressful natural habitats indicates that stress- tolerance allows for its local abundance. Because C. lanceolata can also be successful in more productive areas if competitors are removed, its distribution is restricted by competition. This tradeoff may be responsible for the distribution of restricted, locally abundant species which often specialize on stressful habitats.M.S. (Master of Science