Process rates of aquatic insects across latitude and elevation gradients: Does daily and annual variability lead to greater adaptability in stream insects?
Global climate change is anticipated to impact ecosystems worldwide, yet there is little consensus as to how climate change impacts will differ across temperate and tropical ecosystems. Stream ecosystems will be affected in both temperature and the quantity and timing of stream flow. Organism process rates such as growth and excretion are sensitive to changes in temperature and other abiotic factors. To understand how aquatic organisms respond to changing temperatures across different ecosystems, we measured growth rates of Baetidae mayflies in a reciprocal transplant experiment spanning a ~1000 meter elevation gradient in both the Ecuadorian Andes and the Colorado Rockies. Additionally, we measured excretion rates and tissue stoichiometry of multiple insect taxa across a wide range of stream temperatures in both locations.
Growth rates in Rocky Mountain mayflies were 4-fold higher than in tropical Andean mayflies at similar temperatures. Moreover, growth in Rocky Mountain mayflies displayed stronger responses to altered temperature regimes. Mayflies in temperate systems underwent very quick growth while mayflies from tropical montane sites grew slowly and showed muted responses to altered temperature regimes. In contrast, excretion rates of Andean insects were strongly related to elevation and temperature, while temperatures fluctuated more both daily and seasonally in temperate sites, leading to elevation being a poor predictor of excretion rates in Colorado insects. Our data suggest that aquatic insects in temperate systems are more finely tuned to changing process rates in response to temperature than in tropical systems. We speculate that high plasticity of temperate insects may result from narrow windows of ecological opportunity afforded to montane organisms from highly seasonal environments.