Smaller species but larger stages: Warming effects on inter‐ and intraspecific community size structure

Abstract

Global warming can alter size distributions of animal communities, but the contribution of size shifts within versus between species to such changes remains unknown. In particular, it is unclear if expected body size shrinkage in response to warming, observed at the interspecific level, can be used to infer similar size shifts within species. In this study, we compare warming effects on interspecific (relative species abundance) versus intraspecific (relative stage abundance) size structure of competing consumers by analyzing stage‐structured bioenergetic food web models consisting of one or two consumer species and two resources, parameterized for pelagic plankton. Varying composition and temperature and body size dependencies in these models, we predicted interspecific versus intraspecific size structure across temperature. We found that warming shifted community size structure toward dominance of smaller species, in line with empirical evidence summarized in our review of 136 literature studies. However, this result emerged only given a size–temperature interaction favoring small over large individuals in warm environments. In contrast, the same mechanism caused an intraspecific shift toward dominance of larger (adult) stages, reconciling disparate observations of size responses within and across zooplankton species in the literature. As the empirical evidence for warming‐driven stage shifts is scarce and equivocal, we call for more experimental studies on intraspecific size changes with warming. Understanding the global warming impacts on animal communities requires that we consider and quantify the relative importance of mechanisms concurrently shaping size distributions within and among species.

Fish life histories in a warming climate: a mechanistic basis of change and a community context

“…Warming leads to a shift in species composition, favouring a lower trophic position in the multispecies IGP community in Paper IV and an accumulation of biomass in the smaller adult stage in the consumer-resource community in Paper III. This supports the prediction of smaller species and larger stages when accounting for size dependent effects of warming (Uszko et al 2022). Considering theoretical expectations of reduced energetic efficiency from warming in higher trophic levels (Vucic-Pestic et al 2011;Fussmann et al 2014), there is an important difference in how temperature shapes the energetic efficiency within species preceding the extinction in the two models.…”

“…As body size determines the energy demand and temperature sensitivity of energetic efficiency, size differences between trophic levels can determine how system carrying capacity (a system's ability to hold standing biomass based on environmental conditions) respond to warming (Arim et al 2007;Binzer et al 2012). Because of responses in primary production, carrying capacity should be unimodal over the full biological temperature range, and thus decrease in the higher temperature range (Lemoine 2019;Uszko et al 2022). Consequently, food web responses to warming are predicted to depend on the temperature range examined, how warming changes energetic efficiency across trophic levels, on effects on primary production but also on biomass loss via mortality affecting competition for resources (Vasseur & McCann 2005;Binzer et al 2012).…”

“…An increasing number of studies of dynamic food web models account for within species differences in temperature responses to generate predictions of how a warming climate may reshape animal communities (Ohlberger et al 2011;Lindmark et al 2018Lindmark et al , 2019Uszko et al 2022). This development shows for example that system stability changes in response to temperature can depend on size dependent competition within populations (Ohlberger et al 2011), that warming induces alternative stable states via size dependent predation (Lindmark et al 2019), and that body size dependent effects of warming within populations determines population responses to warming and size shifts towards smaller species through competition (Lindmark et al 2018;Uszko et al 2022). These advances of exploring the implication of between and within species processes for responses to climate warming calls for further assessment, in particular of food webs that rely strongly on body size for species interactions (Werner & Gilliam 1984;Gårdmark & Huss 2020).…”

“…Density dependent growth is common in juvenile stages of fish populations and empirical work support that climate change may reduce such density dependence (Bassar et al 2016;Zimmermann et al 2018). That the underlying cause however may be size dependent effects of warming on energy budgets of adults in relation to that of juveniles is to my knowledge based on theoretical predictions (Lindmark et al 2018;Uszko et al 2022).…”

A size‐based perspective on the decoupling between compositional and functional changes in planktonic communities

“…However, there is still a lack of fully targeted experimental examination on warming‐induced changes in interspecific size structures of zooplankton communities with high species and taxon diversity. Recently, a study reviewed 123 experimental or observational studies on this (Uszko et al, 2022), and a majority of them (91) observed a shift from larger to smaller species, and only 14 reported the opposite effect. Besides, that study reproduced the expected warming effect at the community composition level by modeling.…”