the standard deviation or the standard error of the predictor 
variable. When information is not available for one taxon, the value can be 0 or <code>NA</code></p></td>
    </tr>
    <tr>
      <th>n.intra</th>
      <td><p>Number of times to repeat the analysis generating a random value for the predictor variable.
If NULL, <code>n.intra</code> = 2</p></td>
    </tr>
    <tr>
      <th>x.transf</th>
      <td><p>Transformation for the predictor variable (e.g. <code>log</code> or <code>sqrt</code>). Please u