Compute Pairwise Competition Indices
This function computes competition indices based on pairs of plants, ignoring higher-order interactions.
A spatstat point pattern object (class
Maximum number of nearest neighbors to include as potential competitors. Default is NULL (no restriction).
Maximum radius to search for potential competitors. Default is NULL (no restriction).
Optional user-supplied selection function for choosing competitors. Must have arguments
Competition kernel function for computing the effect of competitor j on the subject plant i. Must have arguments
Traditionally, a competition index for a subject plant i is obtained in two stages: (1) Choose a set of competitors of i by some selection rule. (2) Compute a measure of the effect of each competitor j on plant i, and add over j. This effect of j on i is normally a function of the sizes of both plants and of the distance between them, which we call a competition kernel. The kernel may depend on other plant attributes, like species, and in some rare instances on the distance ranks or on the number of competitors. Conceptually, the first stage is not strictly necessary, it could be replaced by specifying zero kernel values (the effect of the selection is usually to truncate the kernel function beyond some distance). However, a separate selection rule may be more transparent, and may reduce the computational effort of searching for neighbors.
Some simple selection rules can be implemented by giving a value to
maxR. In any case, reasonable limits on these variables may be advisable for reducing computation. If both arguments
maxR are given, the neighbourhood is defined as the intersection of the neighbourhoods specified by these arguments.
More complex rules can be specified by the
select function, with parameters in
select for examples.
Kernel computation is specified by the
kernel function and the parameters in
kernel for examples.
Returns the point pattern
plants, with the competition indices added to
marks(plants) as a data frame column
Requires the spatstat package.
García, O. “Siplab, a spatial individual-based plant modelling system”. Computational Ecology and Software 4(4), 215-222. 2014.
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