spOccupancy fits single-species, multi-species, and integrated
spatial occupancy models using Markov Chain Monte Carlo (MCMC). Models
are fit using Pólya-Gamma data augmentation. Spatial models are fit
using either Gaussian processes or Nearest Neighbor Gaussian Processes
(NNGP) for large spatial datasets. The package provides functionality
for data integration of multiple single-species occupancy data sets
using a joint likelihood framework. For multi-species models,
spOccupancy provides functions to account for residual species
correlations in a joint species distribution model framework while
accounting for imperfect detection. As of v0.4.0,
`spOccupancy`

provides functions for multi-season (i.e.,
spatio-temporal) single-species occupancy models. Below we provide a
very brief introduction to some of the package’s functionality, and
illustrate just one of the model fitting functions. For more
information, see the resources referenced at the bottom of this
page.

You can install the released version of `spOccupancy`

from
CRAN with:

`install.packages("spOccupancy")`

`spOccupancy` Function |
Description |
---|---|

`PGOcc()` |
Single-species occupancy model |

`spPGOcc()` |
Single-species spatial occupancy model |

`intPGOcc()` |
Single-species occupancy model with multiple data sources |

`spIntPGOcc()` |
Single-species spatial occupancy model with multiple data sources |

`msPGOcc()` |
Multi-species occupancy model |

`spMsPGOcc()` |
Multi-species spatial occupancy model |

`lfJSDM()` |
Joint species distribution model without imperfect detection |

`sfJSDM()` |
Spatial joint species distribution model without imperfect detection |

`lfMsPGOcc()` |
Multi-species occupancy model with species correlations |

`sfMsPGOcc()` |
Multi-species spatial occupancy model with species correlations |

`intMsPGOcc()` |
Multi-species occupancy model with multiple data sources |

`tPGOcc()` |
Single-species multi-season occupancy model |

`stPGOcc()` |
Single-species multi-season spatio-temporal occupancy model |

`svcPGBinom()` |
Single-species spatially-varying coefficient GLM |

`svcPGOcc()` |
Single-species spatially-varying coefficient occupancy model |

`svcTPGBinom()` |
Single-species spatially-varying coefficient multi-season GLM |

`svcTPGOcc()` |
Single-species spatially-varying coefficient multi-season occupancy model |

`svcMsPGOcc()` |
Multi-species spatially-varying coefficient occupancy model |

`tMsPGOcc()` |
Multi-species, multi-season occupancy model |

`stMsPGOcc()` |
Multi-species, multi-season spatial occupancy model |

`svcTMsPGOcc()` |
Multi-species, multi-season spatially-varying coefficient occupancy model |

`postHocLM()` |
Fit a linear (mixed) model using estimates from a previous model fit |

`ppcOcc()` |
Posterior predictive check using Bayesian p-values |

`waicOcc()` |
Compute Widely Applicable Information Criterion (WAIC) |

`simOcc()` |
Simulate single-species occupancy data |

`simTOcc()` |
Simulate single-species multi-season occupancy data |

`simBinom()` |
Simulate detection-nondetection data with perfect detection |

`simTBinom()` |
Simulate multi-season detection-nondetection data with perfect detection |

`simMsOcc()` |
Simulate multi-species occupancy data |

`simTMsOcc()` |
Simulate multi-species, multi-season occupancy data |

`simIntOcc()` |
Simulate single-species occupancy data from multiple data sources |

`simIntMsOcc()` |
Simulate multi-species occupancy data from multiple data sources |

To get started with `spOccupancy`

we load the package and
an example data set. We use data on twelve foliage-gleaning birds from
the Hubbard Brook Experimental
Forest, which is available in the `spOccupancy`

package
as the `hbef2015`

object. Here we will only work with one
bird species, the Black-throated Blue Warbler (BTBW), and so we subset
the `hbef2015`

object to only include this species.

```
library(spOccupancy)
data(hbef2015)
<- dimnames(hbef2015$y)[[1]]
sp.names <- hbef2015
btbwHBEF $y <- btbwHBEF$y[sp.names == "BTBW", , ] btbwHBEF
```

`spPGOcc()`

Below we fit a single-species spatial occupancy model to the BTBW
data using a Nearest Neighbor Gaussian Process. We use the default
priors and initial values for the occurrence (`beta`

) and
detection (`alpha`

) coefficients, the spatial variance
(`sigma.sq`

), the spatial range parameter (`phi`

),
the spatial random effects (`w`

), and the latent occurrence
values (`z`

). We assume occurrence is a function of linear
and quadratic elevation along with a spatial random intercept. We model
detection as a function of linear and quadratic day of survey and linear
time of day the survey occurred.

```
# Specify model formulas
<- ~ scale(Elevation) + I(scale(Elevation)^2)
btbw.occ.formula <- ~ scale(day) + scale(tod) + I(scale(day)^2) btbw.det.formula
```

We run the model using an Adaptive MCMC sampler with a target
acceptance rate of 0.43. We run 3 chains of the model each for 10,000
iterations split into 400 batches each of length 25. For each chain, we
discard the first 2000 iterations as burn-in and use a thinning rate of
4 for a resulting 6000 samples from the joint posterior. We fit the
model using 5 nearest neighbors and an exponential correlation function.
We also specify the `k.fold`

argument to perform 2-fold
cross-validation after fitting the full model. Run `?spPGOcc`

for more detailed information on all function arguments.

```
# Run the model
<- spPGOcc(occ.formula = btbw.occ.formula,
out det.formula = btbw.det.formula,
data = btbwHBEF, n.batch = 400, batch.length = 25,
accept.rate = 0.43, cov.model = "exponential",
NNGP = TRUE, n.neighbors = 5, n.burn = 2000,
n.thin = 4, n.chains = 3, verbose = FALSE, k.fold = 2)
```

This will produce a large output object, and you can use
`str(out)`

to get an overview of what’s in there. Here we use
the `summary()`

function to print a concise but informative
summary of the model fit.

```
summary(out)
#>
#> Call:
#> spPGOcc(occ.formula = btbw.occ.formula, det.formula = btbw.det.formula,
#> data = btbwHBEF, cov.model = "exponential", NNGP = TRUE,
#> n.neighbors = 5, n.batch = 400, batch.length = 25, accept.rate = 0.43,
#> verbose = FALSE, n.burn = 2000, n.thin = 4, n.chains = 3,
#> k.fold = 2)
#>
#> Samples per Chain: 10000
#> Burn-in: 2000
#> Thinning Rate: 4
#> Number of Chains: 3
#> Total Posterior Samples: 6000
#> Run Time (min): 1.6487
#>
#> Occurrence (logit scale):
#> Mean SD 2.5% 50% 97.5% Rhat ESS
#> (Intercept) 4.0762 0.6183 3.0681 4.0071 5.4855 1.0019 261
#> scale(Elevation) -0.5203 0.2249 -0.9772 -0.5132 -0.0825 1.0039 984
#> I(scale(Elevation)^2) -1.1806 0.2257 -1.6958 -1.1593 -0.7969 1.0033 244
#>
#> Detection (logit scale):
#> Mean SD 2.5% 50% 97.5% Rhat ESS
#> (Intercept) 0.6647 0.1155 0.4398 0.6623 0.8955 1.0012 5605
#> scale(day) 0.2899 0.0709 0.1507 0.2900 0.4273 1.0020 6000
#> scale(tod) -0.0319 0.0697 -0.1680 -0.0327 0.1055 0.9999 6000
#> I(scale(day)^2) -0.0756 0.0867 -0.2476 -0.0752 0.0926 1.0000 6000
#>
#> Spatial Covariance:
#> Mean SD 2.5% 50% 97.5% Rhat ESS
#> sigma.sq 1.2610 1.0218 0.2063 0.9694 4.0863 1.0130 101
#> phi 0.0093 0.0085 0.0009 0.0056 0.0294 1.0763 45
```

The function `ppcOcc`

performs a posterior predictive
check on the resulting list from the call to `spPGOcc`

. For
binary data, we need to perform Goodness of Fit assessments on some
binned form of the data rather than the raw binary data. Below we
perform a posterior predictive check on the data grouped by site with a
Freeman-Tukey fit statistic, and then use the `summary`

function to summarize the check with a Bayesian p-value.

```
<- ppcOcc(out, fit.stat = 'freeman-tukey', group = 1)
ppc.out summary(ppc.out)
#>
#> Call:
#> ppcOcc(object = out, fit.stat = "freeman-tukey", group = 1)
#>
#> Samples per Chain: 10000
#> Burn-in: 2000
#> Thinning Rate: 4
#> Number of Chains: 3
#> Total Posterior Samples: 6000
#>
#> Bayesian p-value: 0.4828
#> Fit statistic: freeman-tukey
```

The `waicOcc`

function computes the Widely Applicable
Information Criterion (WAIC) for use in model selection and assessment
(note that due to Monte Carlo error your results will differ
slightly).

```
waicOcc(out)
#> elpd pD WAIC
#> -679.88774 22.96844 1405.71235
```

Alternatively, we can perform k-fold cross-validation (CV) directly
in our call to `spPGOcc`

using the `k.fold`

argument and compare models using a deviance scoring rule. We fit the
model with `k.fold = 2`

and so below we access the deviance
scoring rule from the 2-fold cross-validation. If we have additional
candidate models to compare this model with, then we might select for
inference the one with the lowest value of this CV score.

```
$k.fold.deviance
out#> [1] 1414.417
```

Prediction is possible using the `predict`

function, a set
of occurrence covariates at the new locations, and the spatial
coordinates of the new locations. The object `hbefElev`

contains elevation data across the entire Hubbard Brook Experimental
Forest. Below we predict BTBW occurrence across the forest, which are
stored in the `out.pred`

object.

```
# First standardize elevation using mean and sd from fitted model
<- (hbefElev$val - mean(btbwHBEF$occ.covs[, 1])) / sd(btbwHBEF$occ.covs[, 1])
elev.pred .0 <- as.matrix(hbefElev[, c('Easting', 'Northing')])
coords.0 <- cbind(1, elev.pred, elev.pred^2)
X<- predict(out, X.0, coords.0, verbose = FALSE) out.pred
```

The `vignette("modelFitting")`

provides a more detailed
description and tutorial of the core functions in
`spOccupancy`

. For full statistical details on the MCMC
samplers for core functions in `spOccupancy`

, see
`vignette("mcmcSamplers")`

. In addition, see the introductory
spOccupancy paper that describes the package in more detail (Doser
et al. 2022). For a detailed description and tutorial of joint species
distribution models in `spOccupancy`

that account for
residual species correlations, see
`vignette("factorModels")`

,
`vignette("mcmcFactorModels")`

, and our open-access paper (Doser et
al. 2023). For a description and tutorial of multi-season
(spatio-temporal) occupancy models in `spOccupancy`

, see
`vignette("spaceTimeModels")`

. For a tutorial on
spatially-varying coefficient models in `spOccupancy`

, see
`vignette("svcModels")`

and
`vignette(mcmcSVCModels)`

.

Doser, J. W., Finley, A. O., Kery, M., and Zipkin, E. F. (2022a). spOccupancy: An R package for single-species, multi-species, and integrated spatial occupancy models. Methods in Ecology and Evolution. 13(8) 1670-1678. https://doi.org/10.1111/2041-210X.13897.

Doser, J. W., Finley, A. O., and Banerjee, S. (2023). Joint species distribution models with imperfect detection for high-dimensional spatial data. Ecology. https://doi.org/10.1002/ecy.4137.