parametricTP: Parametric trophic position

In tRophicPosition: Bayesian Trophic Position Estimation with Stable Isotopes

Parametric trophic position

Description

Calculation of parametric trophic position (with means) partially based on Post (2002: Using Stable Isotopes to Estimate Trophic Position: Models, Methods, and Assumptions. Ecology 83, 703).

Usage

parametricTP(siData, lambda = 2, print = TRUE)

Arguments

siData	an isotopeData class object.
lambda	numerical value representing trophic level of baseline(s).
print	a logical value to indicate whether the output is printed or not.

Details

In case of the one baseline model, trophic position is calculated as

TP = lambda + ((dNc - dNb1) / deltaN)

where lambda is trophic level of baseline 1, dNc are d15N values of consumer, dNb1 are d15N values of baseline 1 and deltaN are trophic discrimination factor values of N.

In case of the two baselines model, trophic position is calculated as

TP = lambda + ((dNc - ((dNb1 * alpha) + (dNb2 * (1 - alpha)))) / deltaN)

and

alpha = (dCc - dCb2) / (dCb1 - dCb2)

Additional variables are dCc (d13C values of consumer), dNb2 (d15N values of baseline 2), alpha (relative contribution of N from baseline 1), and dCb1 and dCb2 (d13C values of baselines 1 and 2 respectively).

In case of the two baselines full model, trophic position is calculated with the same equation as the two baselines model, but alpha is calculated as

alpha = ((dCc - (deltaC * TP / lambda)) - dCb2) / (dCb1 - dCb2)

and includes deltaC (trophic discrimination factor for C).

In all cases trophic position is calculated based on means of isotope values and trophic discrimination factors. For the two baselines full model, an iteration is needed to get convergence of trophic position, starting with alpha calculated with the two baselines simple model. If no convergence is gotten after 50 iterations a message is plotted and both alpha and trophic position are printed.

Value

a list with parametric trophic position calculated with a one baseline model, a two baselines model and its alpha value, and a two baselines full model and its alpha value.

Examples

consumer <- generateTPData()
parametricTP(consumer)

tRophicPosition documentation built on Dec. 28, 2022, 2:27 a.m.