Mass-length allometry covaries with ecosystem productivity at a global scale

Abstract Aim It is still debated whether allometry, the relationship between body size and body parts, entails merely an evolutionary constraint or can itself evolve. Recently, a hypothesis has been proposed that states that static allometry (allometry measured across individuals at the same developmental stage) can evolve from differences in the developmental pathways between pairs of traits under different nutritional environments. A macroecological prediction stemming from this hypothesis is that allometric coefficients (scaling and allometric factors) should covary with ecosystem productivity. Here, we tested this prediction using a worldwide database of mass¿length allometric equations. Location Worldwide, data distributed across the entire globe. Time period 1967¿2017. Major taxa studied Soil arthropods. Methods We fitted general linear models with the allometric coefficients (the scaling a and allometric b factors) as the dependent variables. The target independent variable was the normalized difference vegetation index, as a proxy of ecosystem productivity. Longitude, absolute latitude and altitude, as well as mean annual temperature and mean annual precipitation were included as both covariates and additional variables of interest. We also included body bauplan (obtained from geometric morphometrics), taxonomic affiliation (a proxy of phylogenetic relationships) and the reciprocal allometric coefficient as covariates in the model. Results We found a strong negative association between both allometric factors and the productivity of the ecosystems, and the effect for the allometric factor b was stronger at lower trophic levels. We also detected strikingly similar effects of geographic and climatic predictors on both allometric factors, suggesting the occurrence of similar selective regimes. Main conclusions The fact that productivity, geography and climate affect the value of mass¿length allometric coefficients has important consequences not only to understand the evolution of allometries, but also for how energy is processed in soil ecosystems across the globe.Ministerio de Educación, Cultura y Deporte. Grant Number: FPU13/04933 Consejo Superior de Investigaciones Científicas. Grant Numbers: CGL2014‐61314‐EXP , CGL2015‐66192‐R Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía. Grant Number: P12‐RNM‐152