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

Aim: 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. Location: Global. Time period: 1990-2021. Major taxa studied:
We searched for reproductive measures across all Metazoa, and identified
19,785 Chordata species, along with 440 species of Arthropoda, Cnidaria,
or Mollusca. Methods: 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. Results: 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. Main Conclusions: 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.