simDynoccSpatial: Simulate data under a dynamic occupancy model with spatial...

In AHMbook: Functions and Data for the Book 'Applied Hierarchical Modeling in Ecology' Vols 1 and 2

Simulate data under a dynamic occupancy model with spatial autocorrelation

Description

Function to simulate detection/nondetection data under a general dynamic site-occupancy model with autocorrelation, including:

* Annual variation in the probabilities of patch persistence, colonization and detection is specified by the bounds of a uniform distribution.

* One covariate is allowed to affect a parameter: a site covariate for psi1, site-by-year covariates for phi and gamma, and an observational covariate for p. Covariates are generated internally from uniform(-2, 2) distributions.

* Additional heterogeneity among sites in persistence and colonization or both.

* Additional detection heterogeneity at the site or survey level, with the possibility of a temporal trend in this heterogeneity over the years. E.g., an annual trend in detection heterogeneity at the site or the survey level is specified by the first and second value, which correspond to the heterogeneity in the first and the last year. Hence, trend.sd.site = c(0, 1) will result in a linear trend in the magnitude of site heterogeneity in detection from 0 in the first year to 1 in the last year.

* A single, spatially structured covariate for habitat suitability may affect all parameters via coefficient beta.XAC; for a biologically reasonable way, choose coefficients with the same sign for all 4 (mediated by underlying density). That spatial covariate is simulated as a Gaussian random field with negative exponential correlation function with 'range parameter' theta.XAC.

* Autologistic effects (beta.Xautolog) in persistence and colonization probability can be chosen, which fits a logistic regression of these parameters on the proportion of occupied neighboring cells (in a queen's or 2nd order neighborhood) during the previous time step.

* Additional detection heterogeneity can be introduced at the site- or the individual survey level, with the possibility of a temporal trend in this heterogeneity. For instance, an annual trend in detection heterogeneity at the site or the survey level is specified by the value in the first and the last year. Hence, trend.sd.site = c(0, 1) will result in a linear trend in the magnitude of site heterogeneity in detection from 0 in the first year to 1 in the last year.

Previous versions used RandomFields, but that is not currently available on CRAN. fields is now used instead, but it cannot deal with large values of side and theta.XAC. If you have RandomFields installed (perhaps by getting it from the CRAN archive), you can load a version of simDynoccSpatial that supports it with source(system.file("RandomFieldsSupport", "simDynoccSpatial.R", package="AHMbook")).

See also simDynoccSpatialData.

Usage

simDynoccSpatial(side = 50, nyears = 10, nsurveys = 3,
      mean.psi1 = 0.4, beta.Xpsi1 = 0,
      range.phi = c(0.8, 0.8), beta.Xphi = 0,
      range.gamma = c(0.1, 0.1), beta.Xgamma = 0,
      range.p = c(0.4, 0.4), beta.Xp = 0,
      theta.XAC = 5000, beta.XAC = c(0, 0, 0, 0), beta.Xautolog = c(0, 0),
      trend.sd.site = c(0, 0), trend.sd.survey = c(0, 0),
      seed.XAC = NA, seed = NULL, show.plots = TRUE, ask.plot = TRUE, verbose = TRUE)

Arguments

side	side length of square simulation area; the number of sites, or cells, M = side^2.
nyears	Number of years (or 'seasons').
nsurveys	Number of replicate surveys (= occasions) within a year.
mean.psi1	average occupancy probability in first year.
beta.Xpsi1	coefficient of environmental covariate in probability of initial occupancy.
range.phi	bounds of uniform distribution from which annual probability of persistence is randomly drawn.
beta.Xphi	coefficient of environmental covariate in probability of persistence.
range.gamma	bounds of uniform distribution from which annual probability of colonization is randomly drawn.
beta.Xgamma	coefficient of environmental covariate in probability of colonization.
range.p	bounds of uniform distribution from which probability of detection is randomly drawn.
beta.Xp	coefficient of environmental covariate in probability of detection.
theta.XAC	'range parameter' of a covariate with exponential spatial correlation (i.e., a Gaussian random field is used as an environmental covariate); must be > 0.
beta.XAC	vector of coefficients of that field for the 4 model parameters: psi1, phi, gamma, and p (in that order).
beta.Xautolog	vector of coefficients of autologistic covariate in the following order: persistence (phi), colonization (gamma); the autocovariate is computed at every season as the proportion of occupied cells in a queen's neighborhood around each cell.
trend.sd.site	initial and final values of sd of normal distribution to model logit-normal noise in p at the site level; a linear trend is assumed over time; if the two values are the same, a constant value is assumed.
trend.sd.survey	initial and final values of sd of normal distribution to model logit-normal noise in p at the 'survey' level; if they are different, a linear trend is assumed over time.
seed.XAC	the seed to be used for simulation of the spatially structured covariate for habitat suitability.
seed	the seed to be used for simulation of values apart from the spatially structured covariate for habitat suitability; using the same value for seed.XAC with different values for seed allows generation of different data sets with the same habitat suitability covariate.
show.plots	if TRUE, summary plots are displayed.
ask.plot	If TRUE, pause between plots of results; set to FALSE if running simulations.
verbose	if TRUE, output will be written to the console.

Value

A list with the values of the arguments input and the following additional elements:

M	scalar, total number of pixels in the study area, side^2
grid	2-column matrix, x and y coordinates of each pixel
amatrix	M x M matrix, [i,j] = 1 if cells i and j are neighbors, 0 otherwise
Xpsi1	side x side matrix, value of covariate affecting initial occupancy
Xphi	side x side x nyears array, value of covariate affecting persistence
Xgamma	side x side x nyears array, value of covariate affecting colonization
Xp	side x side x nsurveys x nyears array, value of covariate affecting detection
XAC	side x side matrix, the spatially correlated covariate
Xauto	side x side x nyears array, the autocovariate, the proportion of neighboring cells occupied
Xautoobs	side x side x nyears array, the observed autocovariate, the proportion of neighboring cells where the species was detected
sd.site	vector nyears, year-specific values of SD of Gaussian random site effects in p
sd.survey	vector nyears, year-specific values of SD of Gaussian random survey effects in p
mean.phi	vector nyears-1, mean persistence for each interval
mean.gamma	vector nyears-1, mean colonization for each interval
mean.p	vector nyears, mean detection probability for each year
psi	side x side x nyears array, probability of occupancy for each site and year
mean.psi	vector nyears, mean occupancy over cells for each year
psi.app	vector nyears, apparent occupancy, proportion of cells where species detected
z	side x side x years array, true occupancy state
zobs	side x side x years array, observed occupancy state
nocc	vector nyears, true number of occupied cells
nocc.obs	vector nyears, number of cells where the species was detected
phi	side x side x nyears-1 array, probability of persistence in each interval between years
gamma	side x side x nyears-1 array, probability of colonization in each interval between years
p	side x side x nsurveys x nyears array, probability of detection
y	side x side x nsurveys x nyears array, the observed detection history
umf	an unmarked data frame object with the simulated data

Author(s)

Marc Kéry & Andy Royle

References

Kéry, M. & Royle, J.A. (2021) Applied Hierarchical Modeling in Ecology AHM2 - 9.

Examples

# Generate data with the default arguments and look at the structure
try(str(simDynoccSpatial()))  # Fails if RandomFields is not available

str(simDynoccSpatial(side=50, theta.XAC=1))

AHMbook documentation built on Sept. 12, 2024, 6:37 a.m.