| Title: | Bayesian Community Ecology Analysis |
|---|---|
| Description: | Bayesian multivariate binary (probit) regression models for analysis of ecological communities. |
| Authors: | Nick Golding and David J. Harris |
| Maintainer: | Nick Golding <[email protected]> |
| License: | GPL (>= 2) |
| Version: | 0.1-2 |
| Built: | 2024-10-01 06:26:01 UTC |
| Source: | CRAN |
BayesComm fits Bayesian multivariate binary (probit) regression models for analysis of ecological communities. These models can be used to make inference about underlying inter-species interactions in communities and to separate the effects of environmental covariates and inter-species interactions on community assembly. This package accompanies the paper (in preparation) by Golding et al. (2013) and is based on a model described by Edwards and Allenby (2003).
| Package: | BayesComm |
| Type: | Package |
| Version: | 0.1-1 |
| Date: | 2014-03-07 |
| License: | GPL (>=2) |
BayesComm models take as input a matrix of species presence/absence records and optionally a matrix of environmental covariates.
BC is the main function for setting up models.
It is a wrapper function to BCfit and returns a bayescomm object.
bayescomm objects have associated summary, plot, print, window and residuals functions.
Functions are also provided to calculate Deviance Information Criteria (DIC) and run a deviance partitioning procedure on model outputs (devpart).
Full details of formulation of the model are given in Golding et al. (2013).
Nick Golding <[email protected]> \& Dave Harris
Golding (2013) Mapping and understanding the distributions of potential vector mosquitoes in the UK: New methods and applications. (Chapter 3) http://dx.doi.org/10.6084/m9.figshare.767289
Edwards, Y., Allenby, G. (2003) Multivariate analysis of multiple response data. Journal of Marketing Research, 40 (3) 321-34.
BC, BCfit,
window.bayescomm, plot.bayescomm, print.bayescomm, summary.bayescomm, residuals.bayescomm,
DIC, devpart,
BC is the main function for running BayesComm models.
It is a wrapper function for BCfit; it checks inputs, sets up the model types and specifies a number of default BCfit settings.
BC(Y, X = NULL, model = "null", covlist = NULL, condition = NULL, its = 100, ...)BC(Y, X = NULL, model = "null", covlist = NULL, condition = NULL, its = 100, ...)
Y |
matrix of species presence/absence data |
X |
matrix of environmental covariates |
model |
type of model to run |
covlist |
optional list of which covariates to assign to each species |
condition |
matrix of conditioning variables |
its |
number of iterations for sampling phase |
... |
further arguments to pass to |
Y must be a matrix with records as rows and species as columns and X a matrix with records as rows and covariates as columns.
model must be one of: "null" (intercept only), "environment" (intercept & covariates), "community" (intercept & community matrix) or "full" (intercept, covariates & community matrix).
covlist must have the same length as the number of species with, each element a vector of column indices for X. covlist defaults to NULL, which includes all covariates for all species.
For more details of arguments for model fitting see BCfit. condition is an optional matrix of conditioning variables.
These are fitted in the same way as X but are not removed in null and community models.
An object of class bayescomm containing the model call and parameter chains which can be viewed and manipulated using window, plot, print and summary.
# create fake data n <- 100 nsp <- 4 k <- 3 X <- matrix(c(rep(1, n), rnorm(n * k)), n) # covariate matrix W <- matrix(rnorm(nsp * nsp), nsp) W <- W %*% t(W) / 2 # true covariance matrix B <- matrix(rnorm(nsp * (k + 1), 0, 3), nsp) # true covariates mu <- apply(B, 1, function(b, x) x %*% b, X) # true mean e <- matrix(rnorm(n * nsp), n) %*% chol(W) # true e z <- mu + e # true z Y <- ifelse(z > 0, 1, 0) # true presence/absence # run BC (after removing intercept column from design matrix) m1 <- BC(Y, X[, -1], model = "full", its = 100)# create fake data n <- 100 nsp <- 4 k <- 3 X <- matrix(c(rep(1, n), rnorm(n * k)), n) # covariate matrix W <- matrix(rnorm(nsp * nsp), nsp) W <- W %*% t(W) / 2 # true covariance matrix B <- matrix(rnorm(nsp * (k + 1), 0, 3), nsp) # true covariates mu <- apply(B, 1, function(b, x) x %*% b, X) # true mean e <- matrix(rnorm(n * nsp), n) %*% chol(W) # true e z <- mu + e # true z Y <- ifelse(z > 0, 1, 0) # true presence/absence # run BC (after removing intercept column from design matrix) m1 <- BC(Y, X[, -1], model = "full", its = 100)
BCfit is the workhorse function for the BayesComm model.
It is highly recommended to use the wrapper function BC which checks inputs and sets up different model types and initial values.
BCfit arguments can be accessed through BC using the ... argument.
BCfit(y, X, covlist, R, z, mu, updateR, iters, thin = 1, burn = 0, priW = c(nrow(z) + 2 * ncol(z), 2 * ncol(z)), verbose = 0)BCfit(y, X, covlist, R, z, mu, updateR, iters, thin = 1, burn = 0, priW = c(nrow(z) + 2 * ncol(z), 2 * ncol(z)), verbose = 0)
y |
matrix of species presence/absence data |
X |
matrix of environmental covariates |
covlist |
optional list of which covariates to assign to each species |
R |
initial values for correlation matrix |
z |
initial values for z |
mu |
initial values for mu |
updateR |
logical; if true the correlation matrix is updated, if false it is fixed at |
iters |
total number of iterations |
thin |
amount to thin the posterior chains. Defaults to 1 (no thinning) |
burn |
number of iterations to discard at the beginning of the chain |
priW |
prior specification for correlation matrix W |
verbose |
how often to print updates to the console. |
priW specifies the inverse Wishart prior on the unknown and unidentifiable covariance matrix W from which the correlation matrix R is derived.
priW is a vector of length two, the first element specifies the degrees of freedom, the second element is multiplied by an identity matrix to form the scale matrix.
The default for priW is c(n + 2p, 2p), where n is the number of records and p is the number of species in the community; this therefore forms the prior: iW(n + 2p, 2pI).
This prior was determined to exert minimal influence on the posterior of R whilst limiting dependence of R on the unidentifiable variance parameters of W.
For further details on how to specify Y, X and covlist see BC.
A list containing elements:
R |
samples from posteriors of the correlation matrix |
B |
samples from posteriors of regression coefficients (a list of matrices) |
z |
samples from posteriors of latent variables z |
Runs a deviance partitioning procedure on a set of four bayescomm objects.
devpart(null, environment, community, full)devpart(null, environment, community, full)
null |
a |
environment |
a |
community |
a |
full |
a |
The deviance partitioning procedure determines the proportion of the null deviance explained by each of the other three model types.
The four model types are those created by BC.
A list containing elements
devpart |
matrix containing the proportion of the null deviance explained by each model for each species |
null |
a matrix containing the mean and 95% credible intervals for the deviance for each species in the null model |
environment |
a matrix containing the mean and 95% credible intervals for the deviance for each species in the evironment model |
community |
a matrix containing the mean and 95% credible intervals for the deviance for each species in the community model |
full |
a matrix containing the mean and 95% credible intervals for the deviance for each species in the full model |
# create fake data n <- 100 nsp <- 4 k <- 3 X <- matrix(c(rep(1, n), rnorm(n * k)), n) # covariate matrix W <- matrix(rnorm(nsp * nsp), nsp) W <- W %*% t(W) / 2 # true covariance matrix B <- matrix(rnorm(nsp * (k + 1), 0, 3), nsp) # true covariates mu <- apply(B, 1, function(b, x) x %*% b, X) # true mean e <- matrix(rnorm(n * nsp), n) %*% chol(W) # true e z <- mu + e # true z Y <- ifelse(z > 0, 1, 0) # true presence/absence # run BC (after removing intercept column from design matrix) null <- BC(Y, X[, -1], model = "null", its = 100) comm <- BC(Y, X[, -1], model = "community",its = 100) envi <- BC(Y, X[, -1], model = "environment", its = 100) full <- BC(Y, X[, -1], model = "full", its = 100) devpart(null, envi, comm, full)# create fake data n <- 100 nsp <- 4 k <- 3 X <- matrix(c(rep(1, n), rnorm(n * k)), n) # covariate matrix W <- matrix(rnorm(nsp * nsp), nsp) W <- W %*% t(W) / 2 # true covariance matrix B <- matrix(rnorm(nsp * (k + 1), 0, 3), nsp) # true covariates mu <- apply(B, 1, function(b, x) x %*% b, X) # true mean e <- matrix(rnorm(n * nsp), n) %*% chol(W) # true e z <- mu + e # true z Y <- ifelse(z > 0, 1, 0) # true presence/absence # run BC (after removing intercept column from design matrix) null <- BC(Y, X[, -1], model = "null", its = 100) comm <- BC(Y, X[, -1], model = "community",its = 100) envi <- BC(Y, X[, -1], model = "environment", its = 100) full <- BC(Y, X[, -1], model = "full", its = 100) devpart(null, envi, comm, full)
Calculates Deviance Information Criteria for bayescomm objects.
DIC(BC)DIC(BC)
BC |
a |
Spiegelhalter, D.J.. Best, N.G., Carlin, B.P., van der Linde, A. (2002). Bayesian measures of model complexity and fit. Journal of the Royal Statistical Society, Series B, 64 (4): 583-639.
m1 <- example(BC)[[1]] DIC(m1)m1 <- example(BC)[[1]] DIC(m1)
plot.bayescomm creates summary plots of a subset of the parameter chains in a bayescomm object using the coda package.
## S3 method for class 'bayescomm' plot(x, chain, ...)## S3 method for class 'bayescomm' plot(x, chain, ...)
x |
a |
chain |
a character string of the parameter chains to plot |
... |
further arguments to pass to |
chain should be one of 'R' (for correlation coefficients) or 'B$sp' where sp is the species of interest (for regression coefficients).
m1 <- example(BC)[[1]] plot(m1, 'R') plot(m1, 'B$sp1')m1 <- example(BC)[[1]] plot(m1, 'R') plot(m1, 'B$sp1')
For each set of parameter values sampled by the model (including values of Z), simulate the occurrence probabilities for each species at each new location.
## S3 method for class 'bayescomm' predict(object, newdata, ...)## S3 method for class 'bayescomm' predict(object, newdata, ...)
object |
A bayescomm object |
newdata |
A data.frame with the same columns as X from the original BC model |
... |
Further arguments passed to or from other methods. |
An array of occurrence probabilities. Rows index locations. Columns index species. Slices index MCMC samples.
David J. Harris (http://davharris.github.io)
# load model from first example m1 <- example(BC)[[1]] # use the first five sites of the training data as newdata newdata <- X[1:5, -1] # get predictions prob <- predict(m1, newdata)# load model from first example m1 <- example(BC)[[1]] # use the first five sites of the training data as newdata newdata <- X[1:5, -1] # get predictions prob <- predict(m1, newdata)
print.bayescomm prints a brief summary of a bayescomm object.
## S3 method for class 'bayescomm' print(x, ...)## S3 method for class 'bayescomm' print(x, ...)
x |
a |
... |
further arguments to pass to |
m1 <- example(BC)[[1]] print(m1) m1m1 <- example(BC)[[1]] print(m1) m1
residuals.bayescomm extracts model residuals from a bayescomm object.
Residuals are calculated based on the mean of the posterior probability of presence.
## S3 method for class 'bayescomm' residuals(object, ...)## S3 method for class 'bayescomm' residuals(object, ...)
object |
a |
... |
other arguments |
m1 <- example(BC)[[1]] m1.res <- residuals(m1)m1 <- example(BC)[[1]] m1.res <- residuals(m1)
summary.bayescomm creates summaries of a subset of the parameter chains in a bayescomm object using the coda package.
## S3 method for class 'bayescomm' summary(object, chain, ...)## S3 method for class 'bayescomm' summary(object, chain, ...)
object |
a |
chain |
a character string of the parameter chains to plot |
... |
further arguments to pass to |
chain should be one of 'R' (for correlation coefficients) or 'B$sp' where sp is the species of interest (for regression coefficients).
m1 <- example(BC)[[1]] summary(m1, 'R') summary(m1, 'B$sp1')m1 <- example(BC)[[1]] summary(m1, 'R') summary(m1, 'B$sp1')
window.bayescomm is window function for bayescomm objects, it calls window.mcmc from the coda package.
Parameter chains are subsetted by start and end and thinned by thin.
## S3 method for class 'bayescomm' window(x, start = NULL, end = NULL, thin = 1, ...)## S3 method for class 'bayescomm' window(x, start = NULL, end = NULL, thin = 1, ...)
x |
a |
start |
start iteration |
end |
end iteration |
thin |
thinning interval |
... |
further arguments to pass to |
If start = NULL (default) the start is taken as the first iteration.
If end = NULL (default) the end is taken as the final iteration.
If thin = 1 (default) all iterations within the window are retained.
A bayescomm object with windowed parameter chains.
m1 <- example(BC)[[1]] m2 <- window(m1, 51, 150, 10)m1 <- example(BC)[[1]] m2 <- window(m1, 51, 150, 10)