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Abstract Thermal performance curves (TPCs) are important tools for predicting the sensitivity of populations to climate change. However, the interactive ways that temperature affects multiple life‐history components lead to different fitness outcomes. These interactions are poorly understood for modular animals, especially over the lifespan of individual colonies, which limits our capacity to connect physiological and demographic responses.The goal of this study was to assess and compare the relationships between temperature and different life‐history components in a modular animal to reveal the mechanisms underlying TPCs for fitness.We reared replicated clones of the marine bryozoanBugula neritinaacross a thermal gradient (16 values) ranging from 23 to 32°C, which reflected the upper thermal range of seasonal variation in the field. TPCs were constructed for survival (measured as zooids states within a colony), growth rate, development to reproductive maturity and reproductive capacity, which were measured over much of the realized lifespan expected under field conditions (~30 days).The effect of temperature was more acute on zooid states rather than whole‐colony survival, and increased temperature increased the frequency of polypide regression. Most colonies reached reproductive maturity up to ~30°C, but growth rate and reproduction decreased at temperatures beyond ~25°C. The decline in reproductive capacity over temperatures above ~25°C was then due to the decline in the production of zooids capable of brooding embryos and zooids transitioning to regressed states up until about 30°C and transitioning to dead state beyond that.Higher temperatures are often considered to affect reproduction by interfering with gametogenesis and post‐zygotic pathways, but in modular animals, changes in growth rate and module states could indirectly cause temperature sensitivity of reproduction. Our study has implications for the role of temperature in driving the sampled population's dynamics by setting the number of generations that occur during the time window when temperatures are conducive to reproduction. Our results also have implications for the generality and predictability of temperature on population persistence across unitary and modular animals. Read the freePlain Language Summaryfor this article on the Journal blog. 

ABSTRACT Warming global temperatures have consequences for biological rates. Feeding rates reflect the intake of energy that fuels survival, growth and reproduction. However, temperature can also affect food abundance and quality, as well as feeding behavior, which all affect feeding rate, making it challenging to understand the pathways by which temperature affects the intake of energy. Therefore, we experimentally assessed how clearance rate varied across a thermal gradient in a filter-feeding colonial marine invertebrate (the bryozoan Bugula neritina). We also assessed how temperature affects phytoplankton as a food source, and zooid states within a colony that affect energy budgets and feeding behavior. Clearance rate increased linearly from 18°C to 32°C, a temperature range that the population experiences most of the year. However, temperature increased algal cell size, and decreased the proportion of feeding zooids, suggesting indirect effects of temperature on clearance rates. Temperature increased polypide regression, possibly as a stress response because satiation occurred quicker, or because phytoplankton quality declined. Temperature had a greater effect on clearance rate per feeding zooid than it did per total zooids. Together, these results suggest that the effect of temperature on clearance rate at the colony level is not just the outcome of individual zooids feeding more in direct response to temperature but also emerges from temperature increasing polypide regression and the remaining zooids increasing their feeding rates in response. Our study highlights some of the challenges for understanding why temperature affects feeding rates, especially for understudied, yet ecologically important, marine colonial organisms.