Widespread shifts in body size within populations and assemblages

Area of Science:

• Ecology and Evolutionary Biology
• Global Change Biology
• Biodiversity Research

Background:

• Global change is altering organismal traits, with body size reduction hypothesized for the Anthropocene.
• Body size is a crucial trait influencing demographic rates and ecosystem functions.

Purpose of the Study:

• To assess the prevalence and drivers of body size changes across multiple taxa over six decades.
• To differentiate between within-species size changes and compositional shifts in driving assemblage body size trends.

Main Methods:

• Analysis of 5025 assemblage time series from 1960 to 2020 across six taxonomic groups.
• Application of the Price equation to partition body size change into within-species and compositional components.

Main Results:

• A prevailing decrease in average body size was detected across assemblages, predominantly influenced by fish.
• Changes in assemblage composition were a more significant driver of body size trends than within-species changes.
• Decreases in body size were often offset by increases in abundance, maintaining stable ecosystem biomass.

Conclusions:

• Global change is causing widespread reductions in organism body size, with compositional shifts playing a key role.
• Understanding both within-species and compositional dynamics is essential for predicting ecological responses to global change.
• Ecosystem biomass stability can be maintained through a trade-off between decreasing body size and increasing population abundance.