Table 2.

Summary of the models examined to explain variation in discontinuous gas-exchange patterns of insects

ModelAnalysisBranch lengthsλAICwi
1. M + V̇CO2 + T m + T a + P + T a P Conventional25.83<0.0001
PhylogeneticEqual0.83−17.820.49
PhylogeneticProportional0.83−7.400.003
2. M + V̇CO2 + T m + O2 Conventional31.15<0.0001
PhylogeneticEqual0.84−15.870.19
PhylogeneticProportional0.83−5.430.001
3. M + V̇CO2 + T m + T a + P + T a P + O2 Conventional27.40<0.0001
PhylogeneticEqual0.83−16.950.32
PhylogeneticProportional0.82−6.710.002
• Model 1, pure hygric; model 2, oxidative damage and hygric; model 3, either oxidative and hygric or chthonic-hygric depending on the signs of the parameters (see Table 3). Each model was tested with an explicit model of phylogenetic relationships among species either incorporated or ignored (the latter actually assumes a star-shaped phylogeny with all species equally closely related and is equivalent to a conventional nonphylogenetic analysis), whereas the phylogenetic models either had equal or proportional branch lengths (see Methods). Models were constructed with the following factors: mass (M, mg), rate of CO2 production (V̇CO2, ml·h−1), measurement temperature (T m, °C), ambient (habitat) temperature (T a, °C), precipitation (P, mm·yr−1), and ambient oxygen (O2). λ is a measure of phylogenetic correlation (32); w i is the Akaike weight, the probability that the model is the correct one of those tested.