A global database of nitrogen and phosphorus excretion rates of aquatic animals.

Animals can be important in modulating ecosystem-level nutrient cycling, although their importance varies greatly among species and ecosystems. Nutrient cycling rates of individual animals represent valuable data for testing the predictions of important frameworks such as the Metabolic Theory of Ecology (MTE) and ecological stoichiometry (ES). They also represent an important set of functional traits that may reflect both environmental and phylogenetic influences. Over the past two decades, studies of animal-mediated nutrient cycling have increased dramatically, especially in aquatic ecosystems. Here we present a global compilation of aquatic animal nutrient excretion rates. The dataset includes 10,534 observations from freshwater and marine animals of N and/or P excretion rates. These observations represent 491 species, including most aquatic phyla. Coverage varies greatly among phyla and other taxonomic levels. The dataset includes information on animal body size, ambient temperature, taxonomic affiliations, and animal body N:P. This data set was used to test predictions of MTE and ES, as described in Vanni and McIntyre (2016; Ecology DOI: 10.1002/ecy.1582).

Stoichiometry of a semi-aquatic plethodontid salamander: intraspecific variation due to location, size and diet.

Ecological stoichiometry provides a framework to investigate an organism's relationship to nutrient cycles. An organism's stoichiometry is thought to constrain its contribution to nutrient cycles (recycling or storage), and to limit its growth and reproduction. Factors that influence the stoichiometry of a consumer are largely unstudied, but what is known is that consumer stoichiometry is influenced by the elemental requirements of the consumer (e.g. for growth, reproduction and cell maintenance) and the availability of elements. We examined whole-body stoichiometry of larval southern two-lined salamanders (Eurycea cirrigera) and described the influence of location, body size, stoichiometry of diet items, and environmental nutrient supply on whole-body stoichiometry. Mean composition of phosphorous was 2.6%, nitrogen was 11.3%, and carbon was 39.6%, which are similar for other aquatic vertebrate taxa. The most significant predictor of whole-body stoichiometry was the site where the samples were collected, which was significant for each nutrient and nutrient ratio. Body size and stoichiometry of diet items were also predictors of Eurycea cirrigera stoichiometry. Our study suggests that spatial differences in environmental nutrient supply have a stronger influence on consumer whole-body stoichiometry among similar-sized larvae compared to life history traits, such as body size or diet.