ctor composed of character values that identify the
names of response variables in <code>dframe</code>.</p></dd>


<dt>subpops</dt>
<dd><p>Vector composed of character values that identify the
names of subpopulation (domain) variables in <code>dframe</code>.
If a value is not provided, the value <code>"All_Sites"</code> is assigned to the
subpops argument and a factor variable named <code>"All_Sites"</code> that takes
the value <code>"All Sites"</code> is added to the <code>dframe</code> data frame.  The
de