Avoiding growing pains in reproductive trait databases: the curse of dimensionality

<p><strong>Aim: </strong>Reproductive output features prominently in many trait databases, but the metrics describing it vary and are often untethered to temporal- and volumetric-dimensions (e.g., fecundity-per-bout). Using such ambiguous reproductive measures to make broadscale comparisons across taxonomic groups will only be meaningful if they show a 1:1 relationship with a reproductive measure that explicitly includes both a volumetric and temporal component (i.e., reproductive mass-per-year). We sought to map the prevalence of ambiguous and explicit reproductive measures across taxa, and explore their relationships with one another to determine the cross-compatibility and utility of reproductive metrics in trait databases.</p> <p><strong>Location: </strong>Global.</p> <p><strong>Time period: </strong>1990-2021.</p> <p><strong>Major taxa studied:</strong> We searched for reproductive measures across all Metazoa, and identified 19,785 Chordata species, along with 440 species of Arthropoda, Cnidaria, or Mollusca.</p> <p><strong>Methods:</strong> We included 37 databases from which we summarised the commonality of reproductive metrics across taxonomic groups. We also quantified scaling relationships between ambiguous reproductive traits (fecundity-per-bout, fecundity-per-year and reproductive mass-per-bout) and an explicit measure (reproductive mass per-year) to assess their cross-compatibility.</p> <p><strong>Results: </strong>Most species were missing at least one temporal or volumetric dimension of reproductive output, such that reproductive mass-per-year could be reconstructed for only 4,786 vertebrate species. Ambiguous reproductive measures were poor predictors of reproductive mass-per-year – in no instance did these measures scale at 1:1.</p> <p><strong>Main Conclusions:</strong> Ambiguous measures systematically misestimate reproductive mass-per-year. Until more data are collected, we suggest authors use the clade-specific scaling relationships provided here to convert ambiguous reproductive measures to reproductive mass-per-year.  </p>