Metabolic theory and the temperature-size rule explain the temperature dependence of population carrying capacity

The temperature dependence of highly conserved subcellular metabolic systems affects ecological patterns and processes across scales, from organisms to ecosystems. Population density at carrying capacity plays an important role in evolutionary processes, biodiversity and ecosystem function, yet how it varies with temperature dependent metabolism remains unclear. Though the exponential effect of temperature on intrinsic population growth rate, r, is well known, we still lack clear evidence that population density at carrying capacity, K, declines with increasing per-capita metabolic rate, as is often assumed in the metabolic theory of ecology (MTE). We experimentally tested whether temperature effects on photosynthesis propagate directly to population carrying capacity in a model species, the mobile phytoplankton Tetraselmis tetrahele. After maintaining populations at constant resource supply and temperatures (6 levels) for 43 days, we found that density declined with increasing temperat...