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 [ 1 Barneche D.R. et al. Fish reproductive-energy output increases disproportionately with body size. Science. 2018; 360 : 642-645 Crossref PubMed Scopus (6) Google Scholar ]. 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 [ 2 Marshall D.J. White C.R. Have we outgrown the existing models of growth?. Trends Ecol. Evol. 2019; 34 : 102-111 Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar ]. The fit of our model to growth data was indistinguishable from that of the well-known models of Pütter [ 3 Pütter A. Studien über psychologische ？hnlichkeit: VI. Wachstums？hnlichkeiten. Pflügers Arch. Gesamte Physiologie Menschen Tiere. 1920; 180 : 298-340 Crossref Scopus (0) Google Scholar ], von Bertallanfy [ 4 von Bertalanffy L. A quantitative theory of organic growth (Inquiries on growth laws. II). Hum. Biol. 1938; 10 : 181-213 Google Scholar , 5 von Bertalanffy L. Quantitative laws in metabolism and growth. Q. Rev. Biol. 1957; 32 : 217-231 Crossref PubMed Google Scholar ], and the ontogenetic growth model (OGM) proposed by West and colleagues [ 6 Hou C. et al. Energy uptake and allocation during ontogeny. Science. 2008; 322 : 736-739 Crossref PubMed Scopus (86) Google Scholar , 7 West G.B. et al. A general model for ontogenetic growth. Nature. 2001; 413 : 628-631 Crossref PubMed Scopus (622) Google Scholar ]. However, these and other existing models of growth [e.g., dynamic energy budget (DEB) theory] [ 8 Kooijman S.A.L.M. Energy budgets can explain body size relations. J. Theor. Biol. 1986; 121 : 269-282 Crossref Google Scholar , 9 Kooijman S.A.L.M. Dynamic Energy Budget Theory for Metabolic Organisation. Cambridge University Press, ; 2010 Google Scholar ] fail to predict hyperallometric reproduction, and we therefore suggested that this disconnect between theory and data requires the revision of existing theory [ 2 Marshall D.J. White C.R. Have we outgrown the existing models of growth?. Trends Ecol. Evol. 2019; 34 : 102-111 Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar ]