Realized thermal niche approach eliminates temperature bias in bioenergetic model estimates

Bioenergetics models estimate ectotherm growth, production, and prey consumption - all key for effective ecosystem management during changing global temperatures. Based on species-specific allometric and thermodynamic relationships, these models typically use the species' lab-derived optimum temperatures (physiological optimum) as opposed to empirical field data (realized thermal niche) that reflect actual thermal experience. Yet, dynamic behavioral thermoregulation mediated by biotic and abiotic interactions may provide substantial divergence between physiological optimum and realized thermal niche temperatures to significantly bias model outcomes. Here, using the Wisconsin bioenergetics model and in-situ year-round temperature data, we tested the two approaches and compared the maximum attainable lifetime weight and lifetime prey consumption estimates for two salmonid species with differing life histories. We demonstrate that using the realized thermal niche is the better approach because it eliminates significant biases in estimates produced by the physiological optimum. Specifically, using the physiological optimum, slower-growing Salvelinus namaycush maximum attainable lifetime weight was underestimated, and consumption overestimated, while fast-growing Oncorhynchus tshawytscha maximum attainable weight was overestimated. While the physiological optimum approach is useful for theoretical studies, our results demonstrate the critical importance that models used by management utilize up-to-date system- and species-specific field data representing actual in-situ behaviors (i.e., realized thermal niche). Bioenergetics models are routinely used to estimate food consumption or growth and are thus critical tools in applied science and decision-making in aquatic ecosystem and species management. Even though fish telemetry is widely used and has enabled researchers to accurately document in-situ temperatures aligned with dynamic fish behavior, that is, their realized thermal niche, the traditional use of lab-derived optimum temperatures based on the physiological optimum theory in models still persists. In this study, we contrasted optimum and field temperature data in models and quantified the effects on growth and consumption of two widely distributed salmonids that occupy both marine and freshwater ecosystems. We demonstrate that significant biases in the model estimates of growth and lifetime prey consumption produced using lab-obtained optimum temperatures could be eliminated by the adoption of realized thermal niche approach to bioenergetics modeling.image