qfasar (version 1.2.1)

pred_beyond_prey: Identify predator signature proportions beyond range of prey

Description

The function pred_beyond_prey identifies predator signaturee proportions that are outside the range of proportions observed in the individual and mean prey signatures.

Usage

pred_beyond_prey(pred_sigs, prey_sigs, mean_sigs)

Arguments

pred_sigs

A numeric matrix of predator signature(s) in column-major format. Intended to be the object pred_sigs returned by the function est_diet.

prey_sigs

A numeric matrix of prey signatures in column-major format. Intended to be the object prey_sigs returned by the function est_diet.

mean_sigs

A numeric matrix of mean prey-type signatures. Intended to be the object prey_sigs returned by the function est_diet.

Value

A list containing the following elements:

beyond_ind

A logical matrix with TRUE indicating that the corresponding predator proportion is outside the range of individual prey proportions.

beyond_mean

A logical matrix with TRUE indicating that the corresponding predator proportion is outside the range of mean prey proportions.

err_code

An integer error code (0 if no error is detected).

err_message

A string contains a brief summary of the execution.

Details

In quantitative fatty acid signature analysis, predator signatues are assumed to be a linear mixture of mean prey signatures (Iverson et al. 2004). Predator signature proportions should therefore be within the range of the prey signature proportions. Signature proportions outside the range of prey proportions are indicative of a violation of one or both of the primary model assumptions, i.e., the prey library is incomplete or the calibration coefficients are inaccurate (Bromaghin et al. 2015, 2016a). Consequently, checking for predator proportions that are outside the range of mean prey proportions is an important diagnostic aid to evaluate the reliability of diet estimates.

The function pred_beyond_prey identifies predator signature proportions that outside the range of proportions observed among the individual and mean prey signatures. For purposes of diet estimation, proportions outside the range of the mean signatures are most important. However, pred_beyond_prey also identifies predator proportions that are outside the range of the individual prey proportions for exploratory purposes.

pred_beyond_prey is designed to be called with inputs returned by the function est_diet. Although it is not conceptually necessary to estimate diets before performing this diagnostic check, doing so ensures that the predator and prey signatures have been transformed to the optimization space (Bromaghin et al. 2015) in which diets have been estimated.

References

Iverson, S.J., C. Field, W.D. Bowen, and W. Blanchard. 2004. Quantitative fatty acid signature analysis: A new method of estimating predator diets. Ecological Monographs 74:211-235.

Bromaghin, J.F., S.M. Budge, G.W. Thiemann, and K.D. Rode. 2016. Assessing the robustness of quantitative fatty acid signature analysis to assumption violations. Methods in Ecology and Evolution 7:51-59.

Bromaghin, J.F., K.D. Rode, S.M. Budge, and G.W. Thiemann. 2015. Distance measures and optimization spaces in quantitative fatty acid signature analysis. Ecology and Evolution 5:1249-1262.

Examples

# NOT RUN {
pred_beyond_prey(pred_sigs = matrix(c(0.05, 0.10, 0.30, 0.55,
                                      0.04, 0.11, 0.29, 0.56,
                                      0.10, 0.05, 0.35, 0.50,
                                      0.12, 0.03, 0.37, 0.48,
                                      0.10, 0.06, 0.35, 0.49,
                                      0.05, 0.15, 0.35, 0.45), ncol = 6),
                 prey_sigs = matrix(c(0.06, 0.09, 0.31, 0.54,
                                      0.05, 0.09, 0.30, 0.56,
                                      0.03, 0.10, 0.30, 0.57,
                                      0.08, 0.07, 0.30, 0.55,
                                      0.09, 0.05, 0.33, 0.53,
                                      0.09, 0.06, 0.34, 0.51,
                                      0.09, 0.07, 0.34, 0.50,
                                      0.08, 0.11, 0.35, 0.46,
                                      0.06, 0.14, 0.36, 0.44), ncol = 9),
                 mean_sigs = matrix(c(0.047, 0.093, 0.303, 0.557,
                                      0.087, 0.050, 0.323, 0.530,
                                      0.077, 0.106, 0.350, 0.467), ncol = 3))

# }