Should I shrink or should I flow? – body size adjustment to thermo-oxygenic niche

Organisms adjust their size according to temperature and supposedly also respond to its negative covariate, oxygen. To what extent is size a response to temperature or oxygen? We analyzed the thermo-oxygenic niche for the community of 188 rotifer species. Evolution toward ranges of thermal tolerance occurred separately from evolution toward their optima. Body size was adjusted to both temperature and oxygen, but the cues for body size response differed; size was either driven by optimal temperatures or by the oxygen tolerance range. Animals are clearly separated into generalists or specialists, and their evolutionary body size adjustment is realized through differential responses to environmental factors. Oxygen is as important as temperature in the evolution of body size and ecological niche preference. An important conclusion from this study is that oxygen deprivation following global warming seems to be as problematic for the studied organisms as the temperature increase itself.