On the exponent in the Von Bertalanffy growth model.

Area of Science:

• Ecology
• Zoology
• Mathematical Biology

Background:

• The Von Bertalanffy growth function (VBGF) models animal mass growth using a differential equation.
• A key parameter, the metabolic scaling exponent (a=2/3), was proposed as universal for vertebrates.

Purpose of the Study:

• To re-evaluate the universality of the metabolic scaling exponent in the VBGF.
• To assess model fit and parameter variability across diverse animal species.

Main Methods:

• Optimization of VBGF parameters, including the exponent (0 ≤ a < 1), for 60 literature datasets (37 fish, 23 non-fish).
• Analysis of parameter variability and data quality's impact on model fit.

Main Results:

• High variability in the optimal exponent was observed across datasets, often without significantly impacting model fit.
• Data quality influenced exponent variability: controlled experiments showed lower variability than natural data.
• Deficiencies like biologically meaningless parameters or boundary solutions were noted in most datasets.

Conclusions:

• The universality of the VBGF's metabolic scaling exponent (a=2/3) is questionable.
• Only 11 of 60 datasets were free of deficiencies, and none supported a universal exponent.