Comparative Elemental Stoichiometry of Ecologically Diverse drosophila

1. Chemical analyses of ecologically diverse species of Drosophila reveal substantial variation among them in their nitrogen and phosphorus contents, determined as a percentage of adult dry mass. Across Drosophila species, the nitrogen content of flies is positively correlated with phosphorus content. 2. For both N and P, the concentration in the flies is correlated with that of their breeding sites. The variation in the elemental composition of breeding sites, and therefore of the flies themselves, may affect the ecology and life-history variation of Drosophila. 3. The range of variation in N and P contents and the N: P ratio is considerably less among Drosophila than among their breeding sites, indicating that there is substantial constancy for elemental composition across Drosophila species. The N: P ratio varies somewhat among species, indicating that the nitrogen and phosphorus contents do not change in perfect proportion across species. 4. An important, but unanswered, question concerns the relation between intraspecific homeostasis and interspecific constancy for elemental composition. Three possible mechanisms by which such interspecific constancy is brought about are discussed.