  Topical discussion networks (TDNs) are networks centered around a discourse
concerning a particular concept, whether in real life or online. This paper
analogises the population of such networks to populations encountered in
mathematical ecology, and seeks to evaluate whether three metrics of diversity
used in ecology - Shannon's $H'$, Simpson's $\lambda$ and $E_{var}$ proposed by
Smith and Wilson - give valuable information about the composition and
diversity of TDNs. It concludes that each metric has its particular use, and
the choice of metric is best understood in the context of the particular
research question.
