Transfer (food, contaminant) across trophic levels

Computes the transfer through a trophic network from lower to higher trophic levels using spatial spreading and flux functions.

Usage

transfer(
  spacemodel,
  kernels,
  fluxes = NULL,
  exposure_weighting = "local",
  verbose = FALSE
)

Arguments

spacemodel

A named list of spatial layers (e.g. SpatRaster objects). Must contain an attribute trophic_tbl of class trophic_tbl.

kernels

A list of kernel parameters for each layer.

fluxes

A trophic_tbl object (or compatible table) containing normalized weights and flux functions for each trophic link.

exposure_weighting

Character. Defines how the realized exposure is calculated based on the predator's presence. Options are:

• "local" (Default): Weight exposure by the local habitat value (`predator_habitat`). Assumes the predator's intake is strictly proportional to the habitat quality/density of the pixel where it resides.

• "diffuse": Weight exposure by a dispersed habitat kernel. Represents a "neighborhood" effect where the predator's presence is smoothed over its home range. Useful to avoid edge effects where a predator on a poor pixel surrounded by good habitat would otherwise have 0 exposure.

• "potential": No weighting. Returns the pure environmental offer (potential exposure) regardless of the predator's density. Useful for identifying risk hotspots.

verbose

Logical. If TRUE, prints progress information.

Value

A named `spacemodel` object as a list of spatial layers representing values after transfer.

Details

The function processes layers in ascending trophic order, as defined by the level attribute of the trophic table.

For each layer:

1. Resources (lower neighbors) are identified.

2. Concentration from each resource is spatially spread using spread().

3. Flux is computed using apply_flux().

4. Contributions from all resources are summed.

The function assumes that flux weights are already normalized so that, for each consumer, the sum of contributions from all resources equals 1.