Data from: Consumption explains intraspecific variation in nutrient recycling stoichiometry in a desert fish

Consumer-driven nutrient recycling can have substantial effects on primary
production and patterns of nutrient limitation in aquatic ecosystems by
altering the rates as well as the relative supplies of the key nutrients
nitrogen (N) and phosphorus (P). While variation in nutrient recycling
stoichiometry has been well-studied among species, the mechanisms that
explain intraspecific variation in recycling N:P are not well-understood.
We examined the relative importance of potential drivers of variation in
nutrient recycling by the fish Gambusia marshi among aquatic habitats in
the Cuatro Ciénegas basin of Coahuila, Mexico. There, G. marshi inhabits
warm thermal springs with high predation pressure as well as cooler,
surface runoff-fed systems with low predation pressure. We hypothesized
that variation in food consumption among these habitats would drive
intraspecific differences in excretion rates and N:P ratios.
Stoichiometric models predicted that temperature alone should not cause
substantial variation in excretion N:P, but that further reducing
consumption rates should substantially increase excretion N:P. We
performed temperature and diet ration manipulation experiments in the
laboratory and found strong support for model predictions. We then tested
these predictions in the field by measuring nutrient recycling rates and
ratios as well as body stoichiometry of fish from nine sites that vary in
temperature and predation pressure. Fish from warm, high-predation sites
excreted nutrients at a lower N:P ratio than fish from cool, low-predation
sites, consistent with the hypothesis that reduced consumption under
reduced predation pressure had stronger consequences for P retention and
excretion among populations than did variation in body stoichiometry.
These results highlight the utility of stoichiometric models for
predicting variation in consumer-driven nutrient recycling within a
phenotypically variable species.