Should We Care If Models Are Phenomenological or Mechanistic?

A recent meta-analysis of published data demonstrated that reproductive output increases disproportionately with size in fish. Building on this observation, we hypothesised that growth slows as animals increase in size because of an increasing allocation of energy to reproduction, and we demonstrated that this hypothesis is plausible by fitting a simple model of energy allocation to growth, reproduction, and maintenance to weight-for-age data for a selection of fish species. The fit of our model to growth data was indistinguishable from that of the well-known models of Pütter, von Bertallanfy, and the ontogenetic growth model (OGM) proposed by West and colleagues. However, these and other existing models of growth [e.g., dynamic energy budget (DEB) theory] fail to predict hyperallometric reproduction, and we therefore suggested that this disconnect between theory and data requires the revision of existing theory.