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.