Scale DEB initial parameters given body mass

[drinky fan]

Hello everyone.

I am simulating the mass dynamics of a viper species under varying microenvironmental and food conditions using the ectotherm function (DEB=1). The microclimate and heat balance model errors are acceptable, but I want to validate the DEB output against field monitoring data (body weight and physical length) of specific individuals.

To set up the validation simulations, I first attempted to derive the initial structure (V) and reserve (E) directly from wet body mass (W_w) and physical length (L_w) using following equations:

1. V = (delta_M * L_w)^3
2. W_wE = W_w - d_wV * V
3. E = W_wE * d_E * mu_E *w_E^-1

However, I am encountering issues with the derived values:

1. Using the default shape coefficient (delta_M) from AmP and a default d_wV of 1 g/cm³, the derived W_wE is consistently negative.
2. I manually calculated delta_M by assuming a cylindrical shape. This yielded a smaller delta_M than the AmP default, but W_wE  still remains mostly negative.
3. I attempted to recalculate structural density as W_w / V_w. This returns a very low value (~0.3), which likely stems from the unreliable cylinder assumption and the use of an estimated diameter (since diameter was not measured during field monitoring).

Am I overlooking a critical theoretical point regarding the translation of field morphology to DEB state variables? I also noticed if E_initial is very low, DEB model will not run in the ectotherm function.

Alternatively, I am considering a simulation-based approach. Would it be sound to (1) run the organism's growth under median temperature and food conditions, (2) extract V and E at the exact point when the simulated organism reaches the mass of our field-caught individuals and (3) using these extracted values as the initial state variables for the actual validation simulation?

Please let me know if any part of my explanation is unclear; I am happy to provide more context. Any insights would be appreciated.

Cheers

Junqi

[NicheMapR]

Hi Junqi,

It can be confusing because in the DEB notation, E has dimension energy and [E] (reserve density) has dimension energy per volume, and the initial conditions are specified using [E]. I haven't tried working through your calculations but I suspect this is part of the problem. Your second approach should work fine and then you should be able to then work out what's going on with your first calculation.

All the best,

Mike