Modeled thermal optima in P_crit curves.

At any given temperature, the model P_crit can be found analytically as the intersection (black dots) of the demand isocline (dashed colored) and the corresponding supply isocline (solid colored), aligning with the curve diagnosed from numerical simulations (solid black). (A) In a model with only diffusive gas exchange characterized by a smaller temperature sensitivity than metabolic demand, the isocline intersections yield an increasing P_crit curve. (B) Conversely, the steeper supply isoclines lead to a decreasing pattern in a single supply step model with ventilation that accelerates faster than metabolic demand. (C) Combining the 2 supply steps in series results in a P_crit curve that is the sum of the single step curves (dotted black), giving rise to a thermal optimum at intermediate temperatures. No experimental data underlie this figure. Code underlying this figure can be found in https://doi.org/10.6084/m9.figshare.24547255.