Testing the Climate Variability Hypothesis in coast-inland systems using the widespread plant Erythranthe guttata

The Climate Variability Hypothesis (CVH) states that organisms in more climatically variable environments are adapted to a wider range of climatic conditions than organisms in less variable environments. The CVH was conceived to explain consistent trends of higher diversity and smaller geographic ranges in the tropics compared to temperate environments. Yet, the underlying assumption that organisms exposed to greater variability will have wider niches can be applied more broadly. Due to marine influence, coastal areas typically experience smaller temperature fluctuations relative to inland areas. According to the CVH, we expect coastal organisms to have more narrow thermal niches because they experience a smaller range of temperatures. We tested the CVH in a novel setting by comparing the thermal niches of coastal and inland populations of Erythranthe guttata using a growth chamber experiment. Preliminary data indicate that inland populations have larger thermal niches than coastal populations, though this does not conform exactly to the CVH. Inland populations performed no better at lower temperatures than coastal populations, though they experience these temperatures more often. This is likely due to physiological limits on performance at these temperatures. Inland populations had higher relative growth rate under higher temperatures, as predicted by the CVH. This holds implications beyond the CVH. If coastal organisms have more narrow thermal niches, they may be more sensitive to temperature increases from climate change. We are continuing this research by using a mechanistic model to understand shifts in suitable habitat for coastal and inland populations and how these populations may respond differently to climate change.