cheddar (version 0.1-639)

Omnivory: 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, ...)

Value

Either a logical vector of length NumberOfNodes or a vector of names.

Arguments

community

an object of class Community.

level

a function that returns the trophic level of each node in community.

...

other values to IsOmnivore.

Author

Lawrence Hudson

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.

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)