Functions to analyze coherence, boundary clumping, and turnover
following the pattern-based metacommunity analysis of Leibold and Mikkelson
Either install from CRAN, or directly from GitHub using the code below. Note that GitHub is the development version of the package, which may or may not differ from what's on CRAN.
# From CRANinstall.packages("metacom")
# From GitHub# install.packages("devtools")devtools::install_github("taddallas/metacom")library("metacom")
'metacom' provides functions for the analysis of the elements of metacommunity structure (coherence, boundary clumping, & turnover), following the pattern-based metacommunity framework of Leibold & Mikkelson 2002 and Presley et al. 2010. This package is designed to allow the user to distinguish between several idealized patterns of metacommunity structure (Presley et al. 2010) utilizing any number of null model algorithms for the randomization procedure. However, these metrics can also be used in isolation, and without ordination via reciprocal averaging, and instead, ordering along some biological gradient.
Definition of a metacommunity:
A metacommunity is a set of sites (e.g. plants in plant-pollinator networks) associated through interactions (e.g. insect species (columns) interact with plant species (rows) in plant-pollinator networks). The pattern-based metacommunity concept, proposed by Leibold & Mikkelson 2002 and expounded on by Presley et al. 2010, allows for the evaluation of metacommunity structure by using randomization techniques to discern between 10 patterns of metacommunity structure. This is performed by ordinating site-by-species interaction matrices and calculating three metrics; coherence, boundary clumping & turnover.
The Elements of Metacommunity Structure Framework:
The metacom package calculates these three metrics; coherence is calculated using the function Coherence(), boundary clumping with BoundaryClump(), and turnover (from either species or range perspective) using the Turnover() function. These functions are consolidated in the metacommunity() function, which can be used to calculate all three metrics. In order to interpret the output of these functions, it will be helpful to read Leibold & Mikkelson 2002 and Presley et al. 2010, but to also read Ulrich and Gotelli 2013, as this paper outlines the difficulty seemingly inherent with investigating community structure. Also, these functions do not have to be used strictly in the Leibold and Mikkelson 2002 framework.
A cautionary note:
I caution the user to be aware that the creation of null matrices can be performed to allow (or not allow) sites to be empty, or species to not exist at any site (i.e. column sums and/or row sums are allowed to be zero). This is controlled by the logical argument 'allow.empty' in the Metacommunity(), NullMaker(), Coherence(), and Turnover() functions. Restricting nulls to not allow empty rows or columns may be biologically realistic, but it also reduces the number of unique null matrices that can be built, which will impact computation time, making it infeasible or impossible in some situations. These situations occur when you have a very sparse interaction matrix, and is also influenced by null model algorithm ('method') that you choose.
The 'metacom' package is partially adapted from previous Matlab code written by Christopher Higgins (available here) and relies on many functions in the 'vegan' package (Oksanen et al. 2012).