The dilemma of altitudinal shifts: caught between high temperature and low oxygen

Abstract

Global warming is expected to drive species toward higher altitudes. Indeed, most documented range shifts are upward, but observed shifts are often far from model predictions, and even downward shifts are common. Can such counterintuitive observations be explained? Metabolic oxygen demand rises with temperature in ectothermic animals, but levels of metabolic sensitivity to temperature increases (Q10) vary among species. Oxygen availability also decreases with altitude, which potentially interferes with the ability of organisms to track their thermal niches upward. Here, I introduce the “metabolic oxygen‐driven altitude shift” (MODAS) framework, which accounts for an overlooked cause of interspecies variation in range shifts. Upward shifts should always occur if it is most important for the species to conserve its pre‐warming temperature. In contrast, if conserving the oxygen demand–supply balance has priority, then downward shifts should occur for species that are less sensitive to temperature increases (low Q10), while excessive upward shifts to lower than pre‐warming temperatures should occur at high Q10.