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Biodiversity collections are experiencing a renaissance fueled by the intersection of informatics, emerging technologies, and the extended use and interpretation of specimens and archived databases. In this article, we explore the potential for transformative research in ecology integrating biodiversity collections, stable isotope analysis (SIA), and environmental informatics. Like genomic DNA, SIA provides a common currency interpreted in the context of biogeochemical principles. Integration of SIA data across collections allows for evaluation of long-term ecological change at local to continental scales. Challenges including the analysis of sparse samples, a lack of information about baseline isotopic composition, and the effects of preservation remain, but none of these challenges is insurmountable. The proposed research framework interfaces with existing databases and observatories to provide benchmarks for retrospective studies and ecological forecasting. Collections and SIA add historical context to fundamental questions in freshwater ecological research, reference points for ecosystem monitoring, and a means of quantitative assessment for ecosystem restoration.

Hydrologic regimes and water temperatures are primary predictors of freshwater species occurrence. Although these variables have been demonstrated to be important in regulating species diversity at particular locations, whether species occurrences across lotic habitats within a single, relatively small watershed can predict the full geographic extent of a species is unclear. We use river reach estimates of streamflow and water temperature derived from a watershed‐scale hydrologic model, coupled with body size measures, to investigate whether the type and variability of thermal and hydrologic habitat used by fish species within the Mobile River Basin (MRB) can predict the overall geographic extent of occurrence (GEO) for these taxa. Locality data for 108 species of fishes within MRB, one of the most ecologically diverse watersheds in the United States, were intersected with streamflow and water temperature estimates to characterize minimum and maximum streamflow and water temperature conditions and thermal breadth (range of thermal conditions) occupied by each species. Among all species, variation in GEO was associated with variation in thermal breadth and body size. Thermal variables were also important predictors of variation in GEO among Cyprinidae. Flow variables were important predictors of variation in GEO for Centrarchidae, Ictaluridae, and Percidae and withinEtheostomaandPercina. Results generally indicate that species with large body size, relatively broad thermal tolerances, or preference for relatively high discharge environments tend to exhibit broader distributions across North America, yet these relationships vary among taxonomic groups.

Predicting the potential effects of changes in climate on freshwater species requires an understanding of the relationships between physiological traits and environmental conditions among populations. While water temperature is a primary factor regulating metabolic rates in freshwater ectotherms, how metabolic rates vary across the species range is unclear. In addition, photoperiod has also been hypothesised to influence metabolic rates in freshwater taxa based on seasonal changes in activity rates. Using an experimental approach, we investigated whether variation in routine metabolic rate (RMR) and sensitivity of RMR to changes in temperature are correlated with local thermal regimes, photoperiods and body mass among ten populations across the geographic range of the Bluntnose minnow (Pimephales notatus), a North American freshwater fish species. Routine metabolic rate data were collected from populations acclimatised to three temperature treatments (9, 18 and 27°C) and correlated with water temperature and photoperiod estimates at collection locations for each population. Routine metabolic rate was negatively correlated with minimum photoperiod at 9°C, negatively correlated with weekly high temperature at 18°C and positively correlated with weekly high temperature at 27°C. Body mass was also a predictor of RMR at each temperature treatment. Thermal sensitivity of RMR was positively correlated with weekly high temperature, indicating that individuals from warmer low latitude populations experienced greater sensitivity of RMR to changes in temperature than individuals from cooler high latitude populations. These results indicate differential responses among populations to variation in temperature and suggest the importance of recognising this variation when characterising responses of freshwater taxa to increases in water temperature.

The Gulf Coast watersheds in the United States contain some of the highest levels of biodiversity of all freshwater systems in North America. Developing environmental management policies to protect and preserve these ecosystems makes the study of the impacts of projected climate change on the future hydrologic cycle crucial. We used the Soil and Water Assessment Tool (SWAT) to estimate the potential hydrologic changes for the mid‐21st century (2050s) and the late 21st century (2080s) in the Mobile River, Apalachicola River, and Suwannee River watersheds in the Gulf Coast region of the United States. These estimates are based on downscaled future climate projections from 20 global circulation models (GCMs) under two representative concentration pathways (RCPs 4.5 and 8.5). SWAT models were calibrated and validated using the multi‐algorithm, genetically adaptive multi‐objective (AMALGAM) technique in a high‐performance computing (HPC) cluster. For the Gulf Coast watersheds, the climate is projected to be warmer and wetter. Projected changes in climatic variables are likely to bring large changes in both annual and seasonal hydrologic processes within these watersheds. We found substantial decreases in mean annual streamflow under RCP8.5 during the 2080s, with up to a 13.0% decrease projected for the Suwannee River watershed compared to the present day. Summer streamflow is projected to be substantially lower during the 2080s, with up to a 25.1% decrease projected for the Suwannee River watershed, during a time of high demand of water resources for agricultural, industrial, and ecosystem services. These hydrologic projections are expected to help in making better‐informed decisions for future water resources and ecosystem management in the Gulf Coast region.