| Omnivory {cheddar} | R Documentation |
Omnivory
Description
Nodes that consume two or more species and have a non-integer trophic level.
Usage
IsOmnivore(community, level=PreyAveragedTrophicLevel)
Omnivores(community, ...)
FractionOmnivorous(community, ...)
Omnivory(community, ...)
Arguments
community |
an object of class |
level |
a function that returns the trophic level of each node in
|
... |
other values to |
Details
Omnivores are those nodes that consume two or more species and have a
non-integer trophic level (Polis 1991). IsOmnivore returns a vector of
logical of length NumberOfNodes; values are TRUE for
nodes that are omnivorous. Omnivores returns the names of nodes for
which IsOmnivore returns TRUE. FractionOmnivorous and
Omnivory both return the proportion of nodes for which IsOmnivore
returns TRUE.
Many researchers have used chain-averaged trophic level when computing omnivory
(Polis, 1991; Bersier et al 2002). Computing chain-averaged trophic level
requires enumerating every unique food chain - this can be lengthy for complex
food webs so the default function used by IsOmnivore is
PreyAveragedTrophicLevel. Omnivory values obtained using these two
methods might differ slightly.
Value
Either a logical vector of length NumberOfNodes or a
vector of names.
Author(s)
Lawrence Hudson
References
Polis, G. A. (1991) Complex desert food webs: an empirical critique
of food web theory. American Naturalist 138, 123–155.
Bersier, L. and Banasek-Richter, C. and Cattin, M. (2002) Ecology 80 2394–2407.
See Also
NumberOfNodes, PreyAveragedTrophicLevel,
ChainAveragedTrophicLevel
Examples
data(TL84)
IsOmnivore(TL84)
Omnivores(TL84)
Omnivory(TL84)
# Omnivory values found using PreyAveragedTrophicLevel and
# ChainAveragedTrophicLevel differ for ChesapeakeBay
data(ChesapeakeBay)
Omnivory(ChesapeakeBay)
Omnivory(ChesapeakeBay, level=ChainAveragedTrophicLevel)