# calc_prefs: Calculate predator-prey size preferences In LeMaRns: Length-Based Multispecies Analysis by Numerical Simulation

## Description

Calculates the size preference of each predator species in each length class for each prey species in each length class.

## Usage

 1 calc_prefs(pred_mu, pred_sigma, wgt, sc_Linf)

## Arguments

 pred_mu A numeric value representing the preferred predator-prey mass ratio. pred_sigma A numeric value representing the width of the weight preference function. wgt A matrix with dimensions nsc and nfish representing the weight of each species in each length class. sc_Linf A numeric vector of length nsc representing the length class at which each species reaches its asymptotic length.

## Details

A predator of species i in length class j has a size preference for species k in length class l equal to

exp(-(log10(wgt[l, k]/wgt[j, i])-pred_mu)^2/(2*pred_sigma)).

## Value

An array of dimensions nsc, nfish, nsc and nfish. The first and second dimensions represent the prey species whereas the third and fourth dimensions represent the predator species.

## References

Hall, S. J., Collie, J. S., Duplisea, D. E., Jennings, S., Bravington, M., & Link, J. (2006). A length-based multispecies model for evaluating community responses to fishing. Canadian Journal of Fisheries and Aquatic Sciences, 63(6):1344-1359.

Ursin, E. (1973). On the prey size preferences of cod and dab. Meddelelser fra Danmarks Fiskeri-og Havundersgelser, 7:85-98.

## Examples

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 # Set up the inputs to the function - species-independent parameters nfish <- nrow(NS_par) nsc <- 32 maxsize <- max(NS_par\$Linf)*1.01 # the biggest size is 1% bigger than the largest Linf l_bound <- seq(0, maxsize, maxsize/nsc); l_bound <- l_bound[-length(l_bound)] u_bound <- seq(maxsize/nsc, maxsize, maxsize/nsc) mid <- l_bound+(u_bound-l_bound)/2 # Set up the inputs to the function - species-specific parameters Linf <- NS_par\$Linf # the von-Bertalanffy asymptotic length of each species (cm). W_a <- NS_par\$W_a # length-weight conversion parameter. W_b <- NS_par\$W_b # length-weight conversion parameter. k <- NS_par\$k # the von-Bertalnaffy growth parameter. Lmat <- NS_par\$Lmat # the length at which 50\% of individuals are mature (cm). # Get phi_min tmp <- calc_phi(k, Linf, nsc, nfish, u_bound, l_bound, calc_phi_min=FALSE, phi_min=0.1) # fixed phi_min phi_min <- tmp\$phi_min # Calculate growth increments tmp <- calc_ration_growthfac(k, Linf, nsc, nfish, l_bound, u_bound, mid, W_a, W_b, phi_min) sc_Linf <- tmp\$sc_Linf wgt <- tmp\$wgt # Calculate predator-prey size preferences prefs <- calc_prefs(pred_mu=-2.25, pred_sigma=0.5, wgt, sc_Linf)

LeMaRns documentation built on Dec. 9, 2019, 5:09 p.m.