Print PageThe traditional stress-competition tradeoff in niche theory states that traits adaptive for high stress environments are maladaptive when competition for shared resources is high. Historically, this tradeoff has been conceptualized as competition for abiotic resources, but biotic interactions, such as competition for pollinator services, are also limiting in many habitats and could lead to the extinction of local populations via reduced reproductive success. In this study, I test the hypothesis that stress-adaptive traits (sensu Chapin’s stress-resistance syndrome) reduce the competitive ability of two plant species endemic to the Ozark glades in comparison to closely-related, widespread congeners. Greenhouse and growth chamber experiments estimated the stress resistance of glade endemics and their widespread congeners to drought and high heat conditions. Individuals of each congeneric pair were exposed to a series of manipulated, abiotic conditions, in accordance with in situ field observations and optimized in the greenhouse, and their fitness responses were compared. In addition, I conducted a field competition experiment in order to explicitly test the role of a stress-reproduction trade-off on the relative competitive abilities of the endemics and their widespread congeners for shared pollinators.
Results/Conclusions
Contrary to our predictions, glade endemic plants were not less resistant to high-stress condition but were better competitors for pollinators in comparison to their widespread congeners. These results indicate that glade endemic plants are not locally adapted to heat or drought stress, and that competition for pollinators, not stress-adaptive traits, may be more important for the maintenance of populations in stressful environments.
