 survivorship and fecundity trajectories. In addition, it is
  sensitive to the length of the these vectors. We direct users to the
  functions `<code><a href="shape_surv.html">shape_surv</a></code>` and `<code><a href="shape_rep.html">shape_rep</a></code>` which
  are relatively robust to these issues.</p>
    </div>
    <div id="references">
    <h2>References</h2>
    <p>Demetrius, L. 1978. Adaptive value, entropy and survivorship
  curves. Nature, 275(5677), 213–214.</p>
<p>Caswell, H. 2001. Matrix Po