title: Experimental whole-stream warming alters community size structure.
abstract: How ecological communities respond to predicted increases in temperature will determine the extent to which Earth's biodiversity and ecosystem functioning can be maintained into a warmer future. Warming is predicted to alter the structure of natural communities, but robust tests of such predictions require appropriate large-scale manipulations of intact, natural habitat that is open to dispersal processes via exchange with regional species pools. Here, we report results of a two-year whole-stream warming experiment that shifted invertebrate assemblage structure via unanticipated mechanisms, while still conforming to community-level metabolic theory. While warming by 3.8 °C decreased invertebrate abundance in the experimental stream by 60% relative to a reference stream, total invertebrate biomass was unchanged. Associated shifts in invertebrate assemblage structure were driven by the arrival of new taxa and a higher proportion of large, warm-adapted species (i.e., snails and predatory dipterans) relative to small-bodied, cold-adapted taxa (e.g., chironomids and oligochaetes). Experimental warming consequently shifted assemblage size spectra in ways that were unexpected, but consistent with thermal optima of taxa in the regional species pool. Higher temperatures increased community-level energy demand, which was presumably satisfied by higher primary production after warming. Our experiment demonstrates how warming reassembles communities within the constraints of energy supply via regional exchange of species that differ in thermal physiological traits. Similar responses will likely mediate impacts of anthropogenic warming on biodiversity and ecosystem function across all ecological communities.
authors.affiliation: Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, 35487 USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Nelson
authors.affiliation: Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, 35487 USA.
authors.forename: Jonathan P
authors.identifier: 0000-0002-2845-1140
authors.initials: JP
authors.lastname: Benstead
authors.affiliation: Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, 35487 USA.
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Huryn
authors.affiliation: Department of Ecology, Montana State University, Bozeman, MT, 59717, USA.
authors.forename: Wyatt F
authors.initials: WF
authors.lastname: Cross
authors.affiliation: Department of Evolution, Ecology and Organismal Biology, The Aquatic Ecology Laboratory, The Ohio State University, Columbus, OH, 43212, USA.
authors.forename: James M
authors.initials: JM
authors.lastname: Hood
authors.affiliation: Department of Civil, Construction and Environmental Engineering, University of Alabama, Tuscaloosa, AL, 35487, USA.
authors.forename: Philip W
authors.initials: PW
authors.lastname: Johnson
authors.affiliation: Department of Ecology, Montana State University, Bozeman, MT, 59717, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Junker
authors.affiliation: Institute of Life and Environmental Sciences, University of Iceland, Reykjavík, Iceland.
authors.forename: Gísli M
authors.initials: GM
authors.lastname: Gíslason
authors.affiliation: Institute of Freshwater Fisheries, Reykjavík, Iceland.
authors.forename: Jón S
authors.initials: JS
authors.lastname: Ólafsson
mesh_terms: D000818:Animals; D044822:Biodiversity; D018533:Biomass; D017753:Ecosystem; D007448:Invertebrates; D013696:Temperature
keywords: body size; community structure; energy demand; metabolic theory; stream warming; thermal preference