Adult body mass influences multi-element stoichiometry in ground beetles

Abstract

The elemental composition of organisms is crucial to their survival and growth, as well as their ecological functions. Although variations in carbon (C), nitrogen (N), and phosphorus (P) among species have been well documented, knowledge on whether such variations also exist within species and hold for other elements is limited. Within species, variations in element concentrations may arise from differences in individual traits (e.g., body mass) or heterogeneities under environmental conditions. To explore whether body mass and environment interactively affect intraspecific multi-element composition, we examined the concentrations of 11 elements (C, N, P, S, K, Ca, Na, Mg, Zn, Mn, and Cu) in 114 individuals from three ground beetle species surveyed in four forest types (poplar, oak, larch and oak-larch mixed forest). We investigated among- and within-species variation in each individual element and in the multi-element composition. Our results showed that (i) across all beetle individuals, body mass and species identity explained most of the variation in the concentrations of most elements, whereas forest type only played a minor role; (ii) within all beetle species, the concentration of C increased with body mass, while that of other elements tended to decrease; and (iii) multidimensional stoichiometric analyses also revealed large variations within species, which were again largely explained by variation in body mass and additionally by forest type. By revealing substantial variation in element composition within species and the role of body mass in driving this variation, our study provides empirical evidence for theoretical modeling of stoichiometry and new insights for integrating morphological and stoichiometric traits.