PRF/J: The Consequences of Resource Availability and Plant Apparency on Patterns of Herbivory and Herbivore Defense in an Annual Tarweed, Hemizonia luzulaefolia

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Ecotypes of Hemizonia Luzulaefolia (Asteraceae) will be used to examine predictions of two theories concerned with the evolution of plant defenses against herbivores: the resource availability and the apparency hypotheses. The resource availability hypothesis predicts that plants adapted to low- resource environments should allocate proportionally more resources to defense than plants adapted to high-resource environments. Two ecotypes of H.luzulaefolia (one adapted to resource-poor serpentine soil and one adapted to resource-rich sandstone soil) in 1) a reciprocal transplant garden experiment to assess this prediction in terms of plant fitness and 2) a container experiment to examine underlying eco-physiological mechanisms) will be used. H.luzulaefolia produces non-resinous rosette leaves prior to flowering and resinous leaves (presumably a defense against herbivores) when flowering is initiated. In addition, two ecotypes differ in flowering time (spring vs.fall) and in quantity of resins produced. The apparency hypothesis predicts that this variation in the timing and quantity of resin production is attributable to variation in vulnerability to herbivores. This idea will be tested by placing different growth stages of the two ecotypes into the grassland at several times during the season and measure herbivore damage. It is anticipated that results generated from these experiments will provide an empirical base for modifying current theory on the evolution of herbivore defense. //