1. Many ectotherms are shifting their distributions polewards, which has been associated with the evolution of phenotypic traits and their thermal plasticity.Trophic interactions may determine the dynamics and ecological impact of range expansions. However, it is largely unknown how trait evolution in edge populations shapes trophic interactions.2. We studied evolutionary changes in the short-term (functional response) and long-term predator-prey interactions between an aquatic insect predator (the damselfly Ischnura elegans) and its prey (the water flea Daphnia magna) during the predator's ongoing poleward range expansion in northern Europe.3. Using a common-garden warming experiment at 20 and 24°C we tested for differentiation between predator populations from edge and core regions in metabolic rate and functional response parameters, and used these empirical data to estimate the effects of range expansion on the short-and long-term predatorprey interaction strengths. 4. Metabolic rates did not differ between populations from edge and core regions nor between rearing temperatures. Functional response parameters and their thermal plasticity showed signals of evolution during the range expansion.Attack rates did not differ between predators from edge and core regions, but only decreased under warming in predators from the edge region. Handling times decreased under warming in predators from the edge region but increased under warming in predators from the core region. While handling times were shorter in predators from the core region at 20°C, these did not differ between regions at 24°C. As a result, the short-term interaction strength was higher for predators from the core region at 20°C, but not different between regions at 24°C. The predator-prey system from the edge region showed lower long-term system stability at 20°C, but this region difference disappeared under warming because the edge region stability then increased. 5. Our results suggest that rapid evolution of functional response parameters during a predator's range expansion reduced the direct feeding impact on its prey and made the predator-prey system from the edge region more unstable, | 3061Functional Ecology CARBONELL et al.

Warming and eutrophication negatively affect freshwater ecosystems by modifying trophic interactions and increasing water turbidity. We need to consider their joint effects on predator–prey interactions and how these depend on the thermal evolution of both predator and prey. We quantified how 4°C warming and algae‐induced turbidity (that integrates turbidity per se and increased food for zooplankton prey) affect functional response parameters and prey population parameters in a common‐garden experiment. We did so for all combinations of high‐ and low‐latitude predator (damselfly larvae) and prey (water fleas) populations to assess the potential impact of thermal evolution of predators and/or prey at a high latitude under warming using a space‐for‐time substitution. We then modelled effects on the system stability (i.e. tendency to oscillate) under different warming, turbidity and evolutionary scenarios. Warming and turbidity had little effect on the functional response parameters of high‐latitude predators. In contrast, warming and turbidity reduced the handling times of low‐latitude predators. Moreover, warming increased the search rates of low‐latitude predators in clear water but instead decreased these in turbid water. Warming increased stability (i.e. prevented oscillations) in turbid water (except for the ‘high‐latitude predator and high‐latitude prey’ system), mainly by decreasing the prey’s carrying capacity and partly also by decreasing search rates, while it did not affect stability in clear water. Algae‐induced turbidity generally decreased stability, mainly by increasing the prey’s carrying capacity and partly also by increasing search rates. This resembles findings that nutrient enrichment can reduce the stability of trophic systems. The expected stability of the high‐latitude trophic system under warming was dependent on the turbidity level: our results suggest that thermal plasticity tends to destabilize the high‐latitude trophic system under warming in clear water but not in turbid water, and that thermal evolution of the predator will stabilize the high‐latitude system under warming in turbid water but less so in clear water. The extent to which thermal plasticity and evolution shape trophic system stability under warming may strongly differ between clear and turbid water bodies, with their contributions having a more stabilizing role in turbid water.

Species may cope with warming through both rapid evolutionary and plastic responses. While thermal performance curves (TPCs), reflecting thermal plasticity, are considered powerful tools to understand the impact of warming on ectotherms, their rapid evolution has been rarely studied for multiple traits. We capitalized on a 2-year experimental evolution trial in outdoor mesocosms that were kept at ambient temperatures or heated 4°C above ambient, by testing in a follow-up common-garden experiment, for rapid evolution of the TPCs for multiple key traits of the water flea Daphnia magna . The heat-selected Daphnia showed evolutionary shifts of the unimodal TPCs for survival, fecundity at first clutch and intrinsic population growth rate toward higher optimum temperatures, and a less pronounced downward curvature indicating a better ability to keep fitness high across a range of high temperatures. We detected no evolution of the linear TPCs for somatic growth, mass and development rate, and for the traits related to energy gain (ingestion rate) and costs (metabolic rate). As a result, also the relative thermal slope of energy gain versus energy costs did not vary. These results suggest the overall (rather than per capita ) top-down impact of D. magna may increase under rapid thermal evolution.