Body size and shape responses to warming and resource competition

Body size is a fundamental trait that impacts many aspects of species biology and ecology. It is in turn influenced by a suite of environmental factors, and often decreases with warming. Although environmental conditions can also impact body shape, which is another functional trait that influences locomotion, resource acquisition, and potentially physiological processes, such responses are poorly understood and rarely quantified. We experimentally tested the independent and combined effects of environmental temperature, resource level, and interspecific competition on the body shape and size responses of two model protist species. We also tested the degree to which these individual-level phenotypic responses are associated with population densities and species coexistence. Body shape was strongly influenced by resource competition, whereas body size changes were mainly driven by environmental temperature. In both species, lower resource levels resulted in body shape elongation, ...