Table 2.

Results from BM (Brownian Motion) and OU (Ornstein–Uhlenbeck) models of evolutionary change. Models including a single evolutionary rate are compared with models fitting separate rates for each migration category (no divide/divide), allowing phenotypic divergence to vary linearly with geographical overlap (overlap) and allowing rates of evolution to vary with both migration category and geographical overlap (no divide/divide and overlap). Models were run with all traits combined (a) and each set of traits separately (bd). OU models include an additional parameter (α) that constrains the rate (β) of divergence to an intermediate value. β slope describes how the evolutionary rate changes with geographical overlap (α was not permitted to vary with geographical overlap); 95% confidence intervals generated using 10 000 bootstraps are shown in parentheses.

Brownian motionOrnstein–Uhlenbeck
βΔAICcββ slope no divideβ slope divideαΔAICc
(a) overall phenotypic divergence
 one rate0.006116.090.018n.a.0.627.82
 no divide/divide0.0097/0.003810.790.040/0.0061n.a.1.18/0.183.73
 overlap0.006617.950.0390.17 (0.0040–3.86)2.905.79
 no divide/divide and overlap0.014/0.00357.880.042/0.00810.0041 (−0.043–5.80)0.078 (−0.0065–2.43)1.29/0.680
(b) song divergence
 one rate0.005320.940.013n.a.0.4813.55
 no divide/divide0.0092/0.002812.440.021/0.0085n.a.0.42/0.693.81
 overlap0.006121.440.0130.0051 (−0.016–1.87)0.0115.74
 no divide/divide and overlap0.013/0.00297.960.015/0.0073−0.01 (−0.033–0.81)0.095 (0.0088–2.62)0.20/1.130
(c) colour divergence
 one rate0.008714.360.020n.a.0.438.32
 no divide/divide0.014/0.00538.590.037/0.0092n.a.0.57/0.243.36
 overlap0.007916.220.0370.20 (0.0061–5.59)2.014.03
 no divide/divide and overlap0.017/0.00528.140.063/0.00910.49 (−0.020–13.57)0.0091 (−0.014–4.29)4.36/0.350
(d) morphological divergence
 one rate0.007820.920.021n.a.0.5614.57
 no divide/divide0.011/0.005617.970.14/0.0059n.a.6.43/0.0184.88
 overlap0.008622.360.170.98 (−0.0095–5.31)11.2910.34
 no divide/divide and overlap0.015/0.004712.590.14/0.012−0.018 (−0.097–0.0013)0.16 (−0.036–6.25)5.71/0.760