A key goal of ecology is to predict when and where resource shortfalls are likely to constrain consumer activity, and hence the work consumers perform in ecosystems. Using principles from metabolic and thermal ecology, we explored how seasonal and diel temperature change shaped both the foraging rate of a prairie ant community and demand for two fundamental resources: salt and sugar. To do this, we ran transects of vials filled with solutions of 0.5% NaCl and 1% sucrose from April through October 2016. We measured ant discovery (if any ant was present in the vial after the 1 hour sampling period) and recruitment (the mean number of ants found per vial of those containing ants). We first confirm a basic prediction rarely tested: the discovery rate of both food resources accelerated with soil temperature, an increase that was typically capped at midday due to extreme surface temperatures. We then tested the novel prediction that sodium demand accelerates with temperature, premised on the assumption that foods like sugars are easily stored in cells while sodium is pumped out of cells at a rate proportional to metabolic rate.
Results/Conclusions
We found that discovery rates of NaCl roughly doubled with increasing soil temperature (p<0.0001) and were suppressed as surface temperatures rose (p=0.0088). We found strong support for our prediction that recruitment to NaCl baits would accelerate with temperature more steeply than recruitment to sucrose baits, across all three times of day (p<0.0008). A follow up experiment in 2017 verified that temperature dependent recruitment to sucrose concentrations of 20%--mimicking rich extrafloral nectaries--was still only half as temperature dependent as recruitment recorded for 0.5% NaCl. These results demonstrate how ecosystem warming accelerates then curtails the work done by a community of ectotherms, and how the demand and use of fundamental nutrients can be differentially temperature dependent.