Widespread reductions in body size are paired with stable assemblage biomass

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 often thought to be shrinking in the Anthropocene. Here, we assess the prevalence of body size change in six taxon groups across 5,032 assemblage time-series spanning 1960-2020. Using the Price equation to partition this change into within-species body size versus compositional changes, we detect prevailing decreases in body size through time. 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 remarkably stable as decreases in body size trade-off with increases in abundance.

Arthropod traits as proxies for abundance trends in the Azorean Islands

“…Body size emerges as a trait that consistently correlates with changes in abundance, with our study adding to this body of literature (Chichorro et al 2022a, b, Martins et al 2023, Martínez-Núñez et al 2024. However, we found different trends depending on the arthropod group.…”

“…higher food demands or large home ranges), lower dispersal ability and lower population densities (Hagge et al 2021, Chichorro et al 2022a, Martins et al 2023, Martínez-Núñez et al 2024. Given the past prevalent habitat and resource loss in Azores (Borges et al 2006, Florencio et al 2013, Terzopoulou et al 2015, it is reasonable to expect that large-bodied species would experience more substantial declines than those with more less demanding resource needs (Purvis et al 2000, Hagge et al 2021, Martins et al 2023.…”

“…Certain characteristics or traits predispose species to decline while other traits will favor the maintenance or even the spread of species (Merckx et al 2018, Wong et al 2019, Chichorro et al 2022a. Such traits correspond to phenotypical and functional characteristics that can describe and predict interactions, vulnerabilities, population trends and extinction risk within human-modified environments (Baeckens et al 2023, Martins et al 2023, Schleuning et al 2023. For instance, when affected by human activities, animals with slow growth and low reproductive rates are at a higher risk of abundance declines and extinction (Merckx et al 2018, Chichorro et al 2022a, Baeckens et al 2023, Martins et al 2023.…”

“…Such traits correspond to phenotypical and functional characteristics that can describe and predict interactions, vulnerabilities, population trends and extinction risk within human-modified environments (Baeckens et al 2023, Martins et al 2023, Schleuning et al 2023. For instance, when affected by human activities, animals with slow growth and low reproductive rates are at a higher risk of abundance declines and extinction (Merckx et al 2018, Chichorro et al 2022a, Baeckens et al 2023, Martins et al 2023. Likewise, despite being energetically expensive, a high dispersal ability (e.g.…”

“…Despite this alarming scenario, we still lack the necessary insight into which species are declining and why (Cardoso et al 2011a, Cardoso andLeather 2019). Depending on the taxon and habitat, results vary widely (Martins et al 2023) and should be seen as a complex interplay of multiple factors, including species traits that influence their susceptibility to anthropogenic change. Therefore, unraveling the effects of species traits on arthropod population trends is crucial to design conservation strategies tailored to arthropod needs, providing evidence for long-term species survival amid human activities (Blüthgen et al 2016, Staab et al 2023.…”