Journal Article body size community structure 27YLU75U4W 7440-44-0 Carbon N762921K75 Nitrogen Phosphorus Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. abundance size spectra allometric scaling biogeography bounded power law climate change ecosystem respiration energy demand freshwater ecology gross primary production headwater streams individual size distributions macroecology macroinvertebrates metabolic theory nutrient cycling nutrient use efficiency stream metabolism stream warming temperature