adj_diet_fat {qfasar}

Adjust diet composition estimates for prey fat content

Description

The function est_diet estimates diet composition in terms of the mass of fatty acids consumed. The function adj_diet_fat uses estimates of fatty acid mass per prey type to transform estimates of diet composition in terms of fatty acid mass to another scale.

Usage

adj_diet_fat(prey_fat, diet_est, diet_var = NA)

Arguments

prey_fat

A numeric vector of the mean fatty acid mass for each prey type.

diet_est

A numeric vector or matrix of the estimated diet composition(s) of individual predator(s) or predator type(s). Intended to be the object est_ind or est_meanreturned by the function est_diet.

diet_var

A numeric matrix or array containing the estimated variance matrix for the estimated diet(s) of individual predator(s) or predator type(s). Intended to be the object var_ind or var_mean) returned by the function est_diet. Optional.

Value

A list containing the following elements:

diet_est

A numeric vector or matrix of the estimated diet composition of individual predator(s) or predator type(s) in terms of the scale represented by prey_fat.

diet_var

A numeric matrix or array containing the estimated variance matrix for the estimated diet of individual predator(s) or predator type(s), in terms of the scale represented by prey_fat.

err_code

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

err_message

A string contains a brief summary of the execution.

Details

The function est_diet estimates diet composition in terms of the mass of fatty acids consumed. Such estimates may be of direct ecological interest, especially for ecosystems in which lipids are particularly important. In other cases, one may wish to transform estimates to a different scale. For example, if the units of prey_fat are (fatty acid mass)/ (animal mass), the function adj_diet_fat returns diet composition estimates in terms of the relative prey mass consumed. Alternatively, if the units of prey_fat are (fatty acid mass)/(animal), the function adj_diet_fat returns diet composition estimates in terms of the relative numbers of prey animals consumed.

adj_diet_fat uses the fat transformation of Iverson et al. (2004). Variance matrices are estimated using the delta method (Seber 1982).

NOTE: values of mass per prey type are treated as known constants without variance.

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.

Seber, G.A.F. 1982. The Estimation of Animal Abundance and Related Parameters, second edition. Macmillan Publishing Co., New York.

Examples

adj_diet_fat(prey_fat = c(0.5, 1, 2),
             diet_est = c(0.3, 0.2, 0.5),
             diet_var = matrix(c( 0.030,  0.004, -0.003,
                                 0.004,  0.025, -0.007,
                                -0.003, -0.007,  0.045),
                               nrow = 3, ncol = 3))

adj_diet_fat(prey_fat = c(0.5, 1, 2),
             diet_est = c(0.3, 0.2, 0.5))