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Calculates the interaction intensity of a food web using the metabolic theory and the interaction dimensionality

Source: R/calcInteractionIntensity.r
calc_interaction_intensity.Rd

The function uses the body mass in Kg of predator/consumer and prey/resources and the dimensionality of the interaction as source data, then the interaction intensity is estimated with all the coefficients from Pawar (2012) as alfa*xR*mR/mC, where alpha is the search rate xR the resource density, mR the resource body mass and mC the consumer body mass. This value of the interaction strength quantifies the effect of the predator on the prey by biomass unit of the predator. Assuming a Lotka-Volterra model is equivalent to the entry A(i,j) of the community matrix, where i is the prey and j the predator.

Usage

calc_interaction_intensity(da, res_mm, res_den, con_mm, int_dim, nsims = 1)

Arguments

da

data.frame with the interactions body mass and type of interaction dimensionality

res_mm

name of the column with the resource body mass mean

res_den

name of the column with the resource density in Individuals/m^2 in 2D or m^3 in 3D. If lower than 0 it uses the previously mentioned estimation.

con_mm

name of the column with the consumer body mass mean

int_dim

name of the column with the interaction dimensionality

Value

A data.frame based on da with the following fields added

  • mR: if res_mm<0 is the resource mass calculated with the equations from ref 1, if res_mm>0 duplicates the value of res_mm

  • xR: calculated resource density or the same value as in the input data.frame.

  • alfa: calculated search rate.

  • qRC: calculated trophic interaction strength as alfa*xR*mR/mC where mC is the consumer body mass.

Details

If the resource density is unknown (parameter res_den) you could set the column to a less than 0 value; and it will be estimated according to the equation S18 and supplementary figures 2i & j (individuals/m2 - m3)

If the mean mass of the resource for detritus or sediment (parameter res_mm) is unknown, it can be designated as negative. This will result in the calculation of the resource body mass (in kilograms) using allometric formulas given in the Equation S9 and Supplementary Figures 2c & d from the paper. This is only valid when the size ratios tend to be optimal.

If the Biomass of the resource is known you should use it as res_mm and set res_den to 1. This is the best choice to avoid the previous allometric calculations of res_den and res_mm when they are unknown.

If resource size res_mm and resource density res_den are decoupled from consumer size you could assign 1 to both see pag 487 Dimensionality and trophic interaction strengths in Pawar's paper.

If the parameter 'nsims > 1 ' the function will estimate the variability on each interaction strength. It takes random values from a normal distribution with mean and standard deviation given by the Pawar's regressions for the slopes of allometric exponents.

References

  1. Pawar, S., Dell, A. I., & Van M. Savage. (2012). Dimensionality of consumer search space drives trophic interaction strengths. Nature, 486, 485. https://doi.org/10.1038/nature11131

Examples

if (FALSE) { # \dontrun{

# Using PotterCove_bm dataset

pc_i <- calc_interaction_intensity(PotterCove_bm,r_bodymass,r_density,c_bodymass,D)
} # }