Number of words in:
Abstract: 145
Main text: 3625
Number of references: 45
Number of figures: 3
Number of tables: 2
Corresponding author: Justin Pomeranz, jfpomeranz@gmail.com, cell: 720.212.9517, Mailing address: University of South Dakota, Department of Biology, 401 East Clark St, Vermillion, SD, USA 57069
Author contributions: JP designed the study, collected the data, performed the modelling work, made the figures and wrote the first draft of the manuscript, JW performed modelling work, made the figures, and all authors contributed substantially to revisions.
Data accessibility: Upon article acceptance, all data and code used in the present study will be archived in Data Dryad and Zenodo, respectively.
Abstract
The distribution of abundance and biomass within ecological communities is related to trophic transfer efficiency from prey to predators. While it is considered to be one of the few consistent patterns in ecology, spatiotemporal variation of this relationship across continental-scale environmental gradients is unknown. Using a database of stream communities collected across North America (18-68° N latitude, -4 to 25°C mean annual temperature) over 3 years, we constructed 162 mass-abundance relationships (i.e. size spectra). Size-spectra slopes declined (became steeper) with increasing temperature. However, the magnitude of change was relatively small, with median slopes changing from -1.2 to -1.3 across a 29°C range in mean annual temperature. In contrast, total community biomass increased 3-fold over the temperature gradient. Our study suggests strong conservation of abundance size-spectra in streams across broad natural environmental gradients. This supports the emerging use of size-spectra deviations as indicators of ecosystem health.