Size‐based ecological interactions drive food web responses to climate warming

Abstract

Predicting climate change impacts on animal communities requires knowledge of how physiological effects are mediated by ecological interactions. Food‐dependent growth and within‐species size variation depend on temperature and affect community dynamics through feedbacks between individual performance and population size structure. Still, we know little about how warming affects these feedbacks. Using a dynamic stage‐structured biomass model with food‐, size‐ and temperature‐dependent life history processes, we analyse how temperature affects coexistence, stability and size structure in a tri‐trophic food chain, and find that warming effects on community stability depend on ecological interactions. Predator biomass densities generally decline with warming – gradually or through collapses – depending on which consumer life stage predators feed on. Collapses occur when warming induces alternative stable states via Allee effects. This suggests that predator persistence in warmer climates may be lower than previously acknowledged and that effects of warming on food web stability largely depend on species interactions.

Experimental evidence of gradual size‐dependent shifts in body size and growth of fish in response to warming

“…A better understanding of how warming effects vary depending on body size is important given that size‐dependent temperature effects yield fundamentally different predictions on how warming affects the dynamics of animal populations (Lindmark et al., , ; Ohlberger et al., ). Temperature effects that depend on body size can, for example, lead to warming‐induced shifts in the regulation (Lindmark et al., ) and dynamics (Ohlberger et al., ) of whole populations and communities (Lindmark et al., ), by affecting species interactions. Therefore, it is important to quantify temperature effects on, for example, growth and how they depend on body size, and the intraspecific size variation it results in (Lindmark et al., ; Ohlberger et al., ), for accurate predictions of population responses to warming.…”

“…The TSR, predicting a plastic increase in initial body growth but a reduction in adult body size with increasing temperature (Atkinson, ), underscores that the nature and strength of climate change effects vary over life history, and that we can only understand population responses to climate change in view of individual development. Still, despite increasing evidence for size‐ and life stage‐specific responses to rising temperatures (Daufresne et al., ; Gardner, Peters, Kearney, Joseph, & Heinsohn, ; Messmer et al., ), most current ecological theory (e.g., Binzer, Guill, Brose, & Rall, ; Vasseur & McCann, ) aiming to explain population responses to temperature variation is based on the assumption of size‐independent effects of warming (e.g., assuming no temperature dependence of allometric exponents of vital rates, such as metabolic rates; but see Lindmark, Huss, Ohlberger, & Gårdmark, ; Lindmark, Ohlberger, Huss, & Gårdmark, ; Ohlberger, Edeline, Vollestad, Stenseth, & Claessen, ). This may be a serious limitation given that life stage and body size have major influences on the physiology (e.g., Brown, Gillooly, Allen, Savage, & West, ) and ecological role of individuals (e.g., Brose, ).…”

Temperature variability alters the stability and thresholds for collapse of interacting species

“…The copyright holder for this preprint (which this version posted May 20, 2020. . https://doi.org/10.1101/2020.05.18.102053 doi: bioRxiv preprint 1 8 addressed in studies of warming of mean temperatures [35,63,64], it remains to be done for increasing temperature variability. Both the complex responses to increasing temperature variability and the importance of accounting also for indirect temperature effects via interacting species that we demonstrate suggest that predicting how temperature variability would impact size-structured food webs cannot be done a priori.…”

Temperature variability alters the stability and thresholds for collapse of interacting species

“…More realistic models 383 (e.g., size-structured, age-structured, or individual-based models) could parse out how 384 maturation, fecundity, mortality, individual growth, and consumption simultaneously respond to 385 thermal regimes in different individuals or size-classes when species interact. For example, 386 accounting for both the temperature-dependent processes underlying body growth and for 387 within-population size structure have proven important for understanding how both consumer 388 populations [35] and food chains [63] vary with temperature. However, while this has been 1 8 addressed in studies of warming of mean temperatures [35, 63,64], it remains to be done for 390 increasing temperature variability.…”

“…For example, 386 accounting for both the temperature-dependent processes underlying body growth and for 387 within-population size structure have proven important for understanding how both consumer 388 populations [35] and food chains [63] vary with temperature. However, while this has been 1 8 addressed in studies of warming of mean temperatures [35, 63,64], it remains to be done for 390 increasing temperature variability. Both the complex responses to increasing temperature 391 variability and the importance of accounting also for indirect temperature effects via interacting 392 species that we demonstrate suggest that predicting how temperature variability would impact 393 size-structured food webs cannot be done a priori.…”