Cost of resistance and tolerance under competition: the defense-stress benefit hypothesis

摘要: Defense costs provide a major explanation for why plants in nature have not evolved to be better defended against pathogens and herbivores; however, evidence defense is often lacking. Plants defend by deploying resistance traits that reduce damage, tolerance the fitness effects of damage. We first tested defense-stress cost (DSC) hypothesis defenses increase become important under competitive stress. In greenhouse experiment, uniparental maternal families host plant Arabis perennans were grown presence absence bunch grass Bouteloua gracilis herbivore Plutella xylostella. Costs manifest as reduced growth herbivory significant when A. grew alone, but environment, contrast DSC hypothesis. then benefit (DSB) may situations thereby reducing net costs. For example, chemical agents also functions interactions. To test DSB hypothesis, we compared differentially populations costs, assuming poorer competitors from less dense habitats likely function competition. Without benefits defenses, expected higher competition accordance with DSB. Populations drummondii differed dramatically competitiveness predicts, only poor competitor population showed However, did differ among populations, suggesting might general stress tolerance. Although explain cases where stress, some decrease