Temperature‐dependent body size effects determine population responses to climate warming

Abstract

Current understanding of animal population responses to rising temperatures is based on the assumption that biological rates such as metabolism, which governs fundamental ecological processes, scale independently with body size and temperature, despite empirical evidence for interactive effects. Here, we investigate the consequences of interactive temperature-and size scaling of vital rates for the dynamics of populations experiencing warming using a stage-structured consumer-resource model. We show that interactive scaling alters population and stage-specific responses to rising temperatures, such that warming can induce shifts in population regulation and stage-structure, influence community structure and govern population responses to mortality. Analysing experimental data for 20 fish species, we found size-temperature interactions in intraspecific scaling of metabolic rate to be common. Given the evidence for size-temperature interactions and the ubiquity of size structure in animal populations, we argue that accounting for size-specific temperature effects is pivotal for understanding how warming affects animal populations and communities.

Is oxygen limitation in warming waters a valid mechanism to explain decreased body sizes in aquatic ectotherms?

“…In summary, despite decades of research it is still unclear how the allocation of energy to different processes (metabolism, growth and reproduction), and their respective efficiencies, relates to size and temperature, and what the underlying mechanisms are. There is some support for different temperature‐dependent allometric exponents of intake and metabolism across fishes (Lindmark, Huss, Ohlberger, & Gardmark, ), which could be due to surface‐volume ratio effects or changes in water viscosity and respiratory costs. If, after accounting for reproductive allocation, energy conversion efficiency to growth is indeed lower at higher temperatures and larger sizes, does oxygen supply play a role?…”

“…How do temperature reaction norms change with acclimation at intra‐ and intergenerational levels? Is the change in temperature dependence different among different processes (e.g., search rate, metabolic rate, escape rate, specific dynamic action and others; Dell et al, ; Dell, Pawar, & Savage, ), and how are they affected by body size (Lindmark et al, )? Answers to these questions are urgently needed for all models that apply individual‐level temperature dependence of physiological rates to predict population and community structure (Barneche et al, ; Brown et al, ). Understanding the costs and benefits of increasing oxygen supply to meet higher metabolic demands in warmer waters.…”

Warmer and browner waters decrease fish biomass production

“…Previously, warming has been shown to lead to smaller mean length (Arranz et al, ; Baudron, Needle, Rijnsdorp, & Tara Marshall, ; Daufresne, Lengfellner, & Sommer, ; Jeppesen et al, ) and an increased proportion of small and young individuals in fish populations (Arranz et al, ; Daufresne et al, ; Jeppesen et al, ; Ohlberger, ). These changes in size distributions can have large consequences for intraspecific interactions and population dynamics (Brose et al, ; Lindmark, Huss, Ohlberger, & Gårdmark, ; Ohlberger, Edeline, Vollestad, Stenseth, & Claessen, ). Similarly, brown water (or higher DOC) has in some cases been shown to result in a lower mean length‐at‐age (Estlander et al, ; Horppila et al, ), lower fish population biomass (Finstad et al, ) and biomass production (Karlsson et al, ).…”

“…Similarly, brown water (or higher DOC) has in some cases been shown to result in a lower mean length‐at‐age (Estlander et al, ; Horppila et al, ), lower fish population biomass (Finstad et al, ) and biomass production (Karlsson et al, ). However, whether these observations from natural systems over relatively small spatial scales (Karlsson et al, ; O'Gorman et al, ) or theoretical predictions (Lindmark et al, ; Ohlberger et al, ) hold for how temperature and water color jointly affect fish biomass production over a large range of natural systems is still unknown.…”

Exploring key issues of aerobic scope interpretation in ectotherms: absolute versus factorial

“…Hypoxia can also have a strong effect on aerobic scope by limiting oxygen supply and reducing MMR (Claireaux and Lagardère 1999). Given the importance of understanding how body size and environmental conditions interact to affect responses to climate change (Lefevre et al 2017;Lindmark et al 2018;Pauly and Cheung 2018), a consideration of how to best quantify changes in aerobic scope due to these factors is clearly warranted.…”