Food web measures
Abstract
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Distance to primary producers
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SpeciesInteractionNetworks.distancetobase — Function.
distancetobase(::Type{SPM}, N::SpeciesInteractionNetwork{<:Unipartite{T}, <:Interactions}, sp::T, f) where {T, SPM <: ShortestPathMethod}
Measures the distance of species sp to a basal species in the food web, where a basal species is defined as having a generaliry of 0.
Following e.g. Thompson et al. (2012), we assign a distance to the base of 1 to the basal species. Primary consumers have a distance of 2, etc.
Post (2002) notes that the trophic level can be obtained from the maximum, mean, or minimum distance to a producer. Given that consumers may be connected to more than one producer, one might argue that the mode or median of these connections may be relevant. For this reason, the function f will consume an array of distances, and return a scalar.
In favor of the minimum, one can argue that most energy transfer should happen along short chains; but imagining a consumer atop a chain of length 5, also connected directly to a producer, the minimum would give it a trophic level of 2, hiding its position at the top of the food web.
In favor of the maximum, one can argue that the higher chains give a better idea of how far energy coming from the bottom of the food web can go. This is a strong indication of how vertically diverse it is (Duffy et al., 2007).
References
Duffy, Cardinale, France, McIntyre, Thébault and Loreau (2007)
distancetobase(N::SpeciesInteractionNetwork{<:Unipartite{T}, <:Interactions}, sp::T) where {T}
Default measure of distancetobase using the BellmanFord shortest paths and the maximum distance.
distancetobase(N::SpeciesInteractionNetwork{<:Unipartite{T}, <:Interactions}, sp::T, f) where {T}
Default measure of distancetobase using the BellmanFord shortest paths and the distance returned by f.