Temperature-Driven Regime Shifts in the Dynamics of Size-Structured Populations

Abstract

Global warming impacts virtually all biota and ecosystems. Many of these impacts are mediated through direct effects of temperature on individual vital rates. Yet how this translates from the individual to the population level is still poorly understood, hampering the assessment of global warming impacts on population structure and dynamics. Here, we study the effects of temperature on intraspecific competition and cannibalism and the population dynamical consequences in a size-structured fish population. We use a physiologically structured consumer-resource model in which we explicitly model the temperature dependencies of the consumer vital rates and the resource population growth rate. Our model predicts that increased temperature decreases resource density despite higher resource growth rates, reflecting stronger intraspecific competition among consumers. At a critical temperature, the consumer population dynamics destabilize and shift from a stable equilibrium to competition-driven generation cycles that are dominated by recruits. As a consequence, maximum age decreases and the proportion of younger and smaller-sized fish increases. These model predictions support the hypothesis of decreasing mean body sizes due to increased temperatures. We conclude that in size-structured fish populations, global warming may increase competition, favor smaller size classes, and induce regime shifts that destabilize population and community dynamics.

Stage-specific biomass overcompensation by juveniles in response to increased adult mortality in a wild fish population

“…In our model we also assume asymmetric competition between life stages. This assumption is supported by physiological observations and modeling results suggesting that smaller-sized perch tend to be more efficient than larger ones in exploiting a common resource (Persson and De Roos 2006, Ohlberger et al 2011a showed that populations are likely to be reproduction limited when juveniles are superior to adults with respect to resource competition (or have lower mortality) and that in such systems increases in mortality induce a compensatory effect in the juvenile stage. The extent of the compensatory response depends on the degree to which mortality rate increases, because juvenile biomass changes with adult mortality according to a hump-shaped relationship , Schro¨der et al 2009).…”

“…First, we do not consider evolutionary change in lifehistory traits, such as changes in size at maturity. Indeed, length at maturity in perch has previously been shown to have slowly increased before but rapidly decreased after the pathogen outbreak, which may have contributed to a shift in reproduction rate (Ohlberger et al 2011a). Although the smaller size at maturation increased the proportion of mature 2-year-old fish, this effect can be assumed to be negligible for the biomass analyses, because the increase was only a few percent (Ohlberger et al 2011a).…”

“…Indeed, length at maturity in perch has previously been shown to have slowly increased before but rapidly decreased after the pathogen outbreak, which may have contributed to a shift in reproduction rate (Ohlberger et al 2011a). Although the smaller size at maturation increased the proportion of mature 2-year-old fish, this effect can be assumed to be negligible for the biomass analyses, because the increase was only a few percent (Ohlberger et al 2011a). Second, Windermere perch were commercially fished at the beginning of our time series (see Appendix), continuing until 1948 in the north and until 1964 in the south basin (Le Cren et al 1977).…”

Effects of Climate Change on Trait-Based Dynamics of a Top Predator in Freshwater Ecosystems

“…Continuous structure due to body size has been studied using detailed physiologically structured population models (Metz and Diekmann 1986), but the method has been applied to only very few wild populations (e.g., Ohlberger et al 2011a). Physiologically structured population models have a continuous timescale and a high level of complexity, and the data requirements are therefore difficult to meet for many wild study populations.…”

Physico-chemical thresholds in the distribution of fish species among French lakes

“…However, fish are poikilotherms and are therefore sensitive to changes in thermal conditions of their environment. Temperature has a direct effect on fish activity, growth, metabolism, reproduction and development but can also influence communities and populations via biotic interactions (Petchey et al, 1999;Voigt et al, 2003;O'Connor et al, 2009;Rall et al, 2010;Yvon-Durocher et al, 2010;Ohlberger et al, 2011;Vucic-Pestic et al, 2011;Reuman et al, 2014). From this viewpoint, 1-3°C increase in temperature due to global warming have been shown to have major impacts on fish community structure and diversity (Daufresne et al, 2004(Daufresne et al, , 2009Daufresne and Boet, 2007).…”