A high-resolution physiological timeseries uncovers strong but variable seasonal acclimation of thermal limits in a copepod community

How a community responds to warming depends on both intra-specific variation in thermal limits and variation in acclimation capacity across community members. These factors, however, are often overlooked, leading to uncertainties about how climate change affects biodiversity. In temperate regions, communities are exposed to large seasonal temperature fluctuations, providing an opportunity to examine community-wide effects of acclimation under natural conditions. Using a weekly physiological time series, we examined seasonal variation in upper thermal limits for the entire community of calanoid copepods in Lake Champlain, a large and highly seasonal lake in North America. Thermal limits varied substantially between species, with winter-dominant species having lower thermal limits than summer-dominant species. Our high-resolution temporal data also revealed substantial but variable acclimation capacities across community members. Hindcasted vulnerability estimates highlight the importance of species-specific estimates of acclimation capacity for robust predictions about the impacts of warming. Over the course of our collections, we also recorded two novel species occurrences in Lake Champlain, both of which were notable for their high upper thermal limits. Our results highlight the importance of acclimation in shaping population responses to temperature variation under natural conditions.