The Climatic Variability Hypothesis and trade-offs in thermal performance in coastal and inland populations of Mimulus guttatus

Abstract

Ecologists and evolutionary biologists have long predicted that organisms in more climatically variable environments should be adapted to handle a wider range of conditions. This intuitive idea, known as the Climatic Variability Hypothesis (CVH), has gained mixed support from empirical studies. We tested the CVH in a novel system by comparing the thermal breadth of coastal and inland populations of Mimulus guttatus. To quantify thermal breadth, we performed a thermal performance experiment and built performance curves. Using these performance curves, we also evaluated evidence for a breadth-performance trade-off and the Hotter-is-Better hypothesis. We did not find support for the CVH; coastal and inland populations did not differ in thermal breadth. However, we found evidence for a breadth-performance trade-off and the Hotter-is-Better hypothesis. Surprisingly, the two most inland populations differed the most in the thermal performance traits we evaluated. Our results highlight the importance of explicitly measuring thermal performance to test explanations of species distribution patterns and the need to examine alternative mechanisms by which organisms occupy different climatic regimes.