Description Functions to estimate the density and size of a spatially distributed animal population sampled with an array of passive detectors, such as traps, or by searching polygons or transects. Models incorporating distance-dependent detection are fitted by maximizing the likelihood. Tools are included for data manipulation and model selection.
License GPL (>= 2)LazyData yes Spatially explicit capture-recapture is a set of methods for studying marked animals distributed in space. Data comprise the locations of detectors (traps, searched areas, etc. described in an object of class 'traps'), and the detection histories of individually marked animals. Individual histories are stored in an object of class 'capthist' that includes the relevant 'traps' object.Models for population density (animals per hectare) and detection are defined in secr using symbolic formula notation. Density models may include spatial or temporal trend. Possible predictors for detection probability include both pre-defined variables (t, b, etc.) corresponding to 'time', 'behaviour' and other effects), and user-defined covariates of several kinds. Habitat is distinguished from nonhabitat with an object of class 'mask'.Models are fitted in secr by maximizing either the full likelihood or the likelihood conditional on the number of individuals observed (n). Conditional likelihood models are limited to homogeneous Poisson density, but allow continuous individual covariates for detection. A model fitted with secr.fit is an object of class secr. Generic methods (plot, print, summary, etc.) are provided for each object class.A link at the bottom of each help page takes you to the help index. Several vignettes complement the help pages:General interest secr-overview.pdf general introduction secr-datainput.pdf data formats and input functions secr-manual.pdf consolidated help pages secr-tutorial.pdf introductory tutorial secr-habitatmasks.pdf buffers and habitat masks secr-models.pdf linear models in secr secr-troubleshooting.pdf problems with secr.fit, including speed issuesMore specialised topics secr-densitysurfaces.pdf modelling density surfaces secr-finitemixtures.pdf mixture models for individual heterogeneity secr-markresight.pdf mark-resight data and models secr-multisession.pdf multi-session capthist objects and models secr-noneuclidean.pdf non-Euclidean distances secr-parameterisations.pdf alternative parameterisations sigmak, a0 secr-polygondetectors.pdf using polygon and transect detector types secr-sound.pdf analysing data from microphone arrays secr-varyingeffort.pdf variable effort in SECR modelsThe datasets possum, skink, ovenbird, housemouse, deermouse, ovensong, hornedlizard and stoatDNA include examples of fitted models.Two add-on packages extend the capability of secr and are documented separately. secrlinear enables the estimation of linear density (e.g., animals per km) for populations in linear habitats such as stream networks (secrlinear-vignette.pdf). secrdesign enables the assessment of alternative study designs by Monte ...