Meeting Abstract
Climate change is expected to shift species distributions as populations grow in favorable habitats and decline in harsh ones. For montane animals, the ability to escape hot, dry conditions at low elevation may be limited by cold temperatures, variable snowpack, and low oxygen at high elevation. The willow beetle Chrysomela aeneicollis is restricted to high elevation habitats in the southernmost part of its range, California’s Sierra Nevada. From 2008-2017, beetle abundance and distribution was measured along steep elevation gradients (2500-3600 m) at 45 sites in 7 creek drainages. Loggers deployed at each site captured annual variation in air temperature and snowpack. The elevation at which peak adult abundance occurs has shifted significantly upwards in the past decade; furthermore, abundance at these elevations has declined precipitously, particularly during a recent severe drought. Abundance was also inversely correlated with winter air temperature. To investigate physiological mechanisms driving distribution shifts, we measured metabolic rate (adults) and running speed (larvae, adults) at high elevation, before and after heat treatment, for beetles held at high or low elevation in the laboratory. Adults held at high elevation had higher metabolic rates and running speeds after heat treatment than those held at low elevation, and high-elevation larvae recovered running speed after treatment more effectively than their low elevation counterparts. These results suggest that continuing to “move up the mountain” to escape hot, dry conditions may be feasible via phenotypic plasticity in metabolism, but may result in reduced population size, increasing the risk of extinction as climate change proceeds.
