Table 1 Estimates of model fit for a neutral and an adaptive model of evolution for mean body mass.

From: Rapid adaptive phenotypic change following colonization of a newly restored habitat

Trait

Model

logL

K

AICc

Akaike weights

LRT

Body mass

Neutral

30.45

2

−56.10

0.002

 
 

Adaptive

36.73

4

−62.38

0.998

12.55, P=0.002

  1. Neutral evolution was modelled as an unbiased random walk, and adaptive evolution was modelled as an Ornstein–Uhlenbeck (OU) process. For the OU model, the adaptive optimum (θ) for log body mass is 2.42, the step variance (σ2step) is 0.0004 and the alpha (α), the strength of the restraining force around the optimum, is 0.39. The log-likelihood (logL), number of parameters (K), bias-corrected Akaike Information Criterion (AICc) and Akaike weights suggest that the adaptive model is the more likely model. A likelihood ratio test (LRT), which tests the significance of the improved fit of the adaptive over the neutral model, with the latter treated as the null model, confirmed that indeed the observed changes in body mass are of an adaptive nature. The LRT statistic is distributed as a χ2, with two degrees of freedom.
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