Epsilon Open Archive

Abstract

Climate warming impacts organisms directly through changes in their physiology. Empirical evidence suggest warming has already led to changes in growth, body size, population and community size-structure of natural populations. However, it is difficult to understand the underlying mechanisms from observational data alone. Therefore, it is important to develop mechanistic population- and food web models grounded in a physiological description of individual life history. This requires knowledge on how physiological processes scale with body size and temperature within species and how those are mediated by ecological interactions, which hitherto is largely unexplored. In this thesis, I collated data sets through standardized literature searches to understand how body growth, metabolism and consumption rate scale with body mass within species of fish using hierarchical modelling approaches. I also expanded population and food web models to include temperature dependence of physiological rates. I characterize the intraspecific scaling of abovementioned rates and find that the optimum growth temperature of an individual fish declines as it grows in body mass. Using dynamical models, I show that even simple stage-structure within species together with food dependent ontogenetic development can lead to very different responses to warming compared to similar, but unstructured, population and community models. These include sudden shifts in stage-structure, collapses of top predators and bistability. Analysis of a size-structured model reveals that initial warming can lead to faster growth rates, but this does not lead to larger-sized populations if also basal resources decline with warming. These findings contribute to a broader understanding of the role of intraspecific sizevariation for understanding how climate change impacts population and community structure and dynamics. They also highlight the importance of evaluating physiological responses to warming in an ecological context, as optimum temperatures for growth decline with both body size and reduced food availability.