Body size shifts in ectotherms are mostly attributed to the Temperature Size Rule stating that warming speeds up initial growth rate but leads to smaller size when food availability does not limit growth. Nevertheless, climate warming can decrease food availability, which can influence growth, fecundity and survival. However, the interactive effects of temperature and food availability on life history traits have been mostly studied in small invertebrate species. In contrast, we have limited information on how temperature and food availability jointly influence life history traits in vertebrate predators and how changes in different life history traits combines to influence population demography. We investigated the independent and interactive effects of temperature and food availability on traits of the medaka fish Oryzias latipes. We used our empirical estimates of vital rates as input parameters of an Integral Projection model to predict how modifications in vital rates translate into population demography. Our results confirm that warming leads to a higher initial growth rate and lower size leading to crossed growth curves between the two temperatures. Food-restricted fish were smaller than ad libitum fed fish throughout the experiment. Fish reared at 30 °C matured younger, had smaller size at maturity, had a higher fecundity but had a shorter life span than fish reared at 20 °C. Food restriction increased survival under both temperature conditions. Warming reduces generation time and increases mean fitness in comparison to the cold treatments. Food restriction increased generation time and fitness in the cold treatment but had no effect in the warm treatment. Our results highlight the importance of accounting for the interaction between temperature and food availability to understand how body size shifts can affects vital rates and population demography. This is of importance in the context of global warming as resources are predicted to change with increasing temperatures.

Species invasions are predicted to increase in frequency with global change, but quantitative predictions of how environmental filters and species traits influence the success and consequences of invasions for local communities are lacking. Here we investigate how invaders alter the structure, diversity and stability regime of simple communities across gradients of habitat productivity, temperature, and community size structure. We examine all three-species trophic modules (apparent and exploitative competition, trophic chain and intraguild predation) with empirically derived temperature and body mass scaling of vital rates. We show that the success of an invasion and its effects on community stability and diversity are predictably determined by the effects of environmental factors on each species and the relative strengths of trophic interactions between resident and invading species. We predict that successful invaders include smaller competitors and comparatively small predators, suggesting that species invasions may facilitate the downsizing of food webs under global change.

Observed body size shifts in ectotherms are mostly attributed to the temperature size rule (TSR) stating that warming speeds up initial growth rate but leads to smaller size when food availability does not limit growth. However, climate warming can decrease food availability and we have limited information on how temperature and food jointly influence life history traits and population fitness. We investigated under laboratory conditions the independent and interactive effects of temperature (20 °C and 30 °C) and food availability (restricted or ad libitum) on the growth, fecundity and survival of the medaka fish Oryzias latipes. We next used our empirical estimates of vital rates as input parameters of an Integral Projection model (IPM) to predict how modifications in vital rates translate into population demographic parameters. Warming leads to a higher initial growth rate and lower size leading to crossed growth curves between the two temperatures. Food-restricted fish were smaller than ad libitum fed fish throughout the experiment, leading to nested growth curves. Fish reared at 30 °C matured younger, had smaller size at maturity, had a higher fecundity but had a shorter life span than fish reared at 20 °C. Food restriction increased survival probabilities under both temperature conditions. According to the IPM, warming reduces generation time and increases mean fitness in comparison to the cold treatments. Food restriction increased generation time and fitness in the cold treatment but had no effect in the warm treatment. Our results show that temperature and food interact on vital rates and population demographics. This is important in the context of global warming, as resources are expected to change with increasing temperatures.

1. The balance between risk and benefit of exploiting resources drives life history evolution. Predators are naturally recognized as major drivers of the life history evolution of their prey. The concept of an evolutionary arms race posits that prey also influence the life history evolution of their predators. There is far more evidence on the role of predators than of prey. 2. The goal of this study was to investigate the role of prey in life history evolution of predators using ladybird beetle predators either of aphids or coccids. These particular organisms were chosen because literature shows that the pace of life of aphids is faster than that of coccids and this difference is reflected in the life histories of the ladybirds that specialize on feeding on aphids or coccids. 3. Thirty-four species of ladybird predators of aphids and eight of coccids belonging to five different tribes were collected and reared in the laboratory. The females were weighed as well as their eggs, and their reproductive investment calculated as the number of ovarioles multiplied by the average mass of an egg. Phylogenetic relatedness was controlled for in the statistical analyses. 4. Controlling for female mass revealed that ladybird predators of aphids lay bigger eggs and have a higher reproductive investment than ladybird predators of coccids. These differences are not influenced by phylogenetic relatedness but only by the type of prey. We suggest that ladybird predators of coccids lay smaller eggs because neonate larvae do not have to search, catch and subdue prey, and that they have a smaller reproductive investment because they need to allocate more resources to locate prey. 5. Recognizing the influence of prey on the life history evolution of predators is important for understanding food web dynamics.