Résumé
1.Stoichiometric differences among organisms can affect trophic interactions and rates of nutrient cycling within ecosystems. However, we still know little about either the underlying causes of these stoichiometric differences, or the consistency of these differences across large geographic extents. 2.Here we analyze elemental (carbon, nitrogen, phosphorus) composition of 872 aquatic macroinvertebrates (71 species) inhabiting tank bromeliads (n = 140) from five distantly located sites across Central and South America to (1) test phylogenetic, trophic and body size scaling explanations for why organisms differ in elemental composition, and (2) determine if patterns in elemental composition are universal or context-dependent. 3.Taxonomy explained most variance in elemental composition, even though phylogenetic signals were weak and limited to regional spatial extents and to the family level. The highest elemental contents and lowest carbon:nutrient ratios were found in organisms at high trophic levels and with smaller body size, regardless of geographic location. 4.Carnivores may have higher nutrient content and lower carbon:nutrient ratios than their prey, as organisms optimize growth by choosing the most nutrient-rich resources to consume and then preferentially retain nutrients over carbon in their bodies. Smaller organisms grow proportionally faster than large organisms, and so are predicted to have higher nutrient requirements to fuel RNA and protein synthesis. Geography influenced the magnitude, more than the direction, of the ecological and/or phylogenetic effects on elemental composition. 5.Overall, our results show that both ecological (i.e., trophic group) and evolutionary drivers explain among-taxa variation in the elemental content of invertebrates, whereas intraspecific variation is mainly a function of body size. Our findings also demonstrate that restricting analyses of macroinvertebrate stoichiometry solely to either the local scale or species level affects inferences of the patterns in invertebrate elemental content, and their underlying mechanisms.