Widespread shifts in body size within populations and assemblages

Martins, Inês S. and Schrodt, Franziska and Blowes, Shane A. and Bates, Amanda E. and Bjorkman, Anne D. and Brambilla, Viviana and Carvajal-Quintero, Juan and Chow, Cher F. Y. and Daskalova, Gergana N. and Edwards, Kyle and Eisenhauer, Nico and Field, Richard and Fontrodona-Eslava, Ada and Henn, Jonathan J. and van Klink, Roel and Madin, Joshua S. and Magurran, Anne E. and McWilliam, Michael and Moyes, Faye and Pugh, Brittany and Sagouis, Alban and Trindade-Santos, Isaac and McGill, Brian J. and Chase, Jonathan M. and Dornelas, Maria (2023) Widespread shifts in body size within populations and assemblages. Science, 381 (6662). pp. 1067-1071. ISSN 0036-8075

Abstract

Biotic responses to global change include directional shifts in organismal traits. Body size, an integrative trait that determines demographic rates and ecosystem functions, is thought to be shrinking in the Anthropocene. Here, we assessed the prevalence of body size change in six taxon groups across 5025 assemblage time series spanning 1960 to 2020. Using the Price equation to partition this change into within-species body size versus compositional changes, we detected prevailing decreases in body size through time driven primarily by fish, with more variable patterns in other taxa. We found that change in assemblage composition contributes more to body size changes than within-species trends, but both components show substantial variation in magnitude and direction. The biomass of assemblages remains quite stable as decreases in body size trade off with increases in abundance.