Estimate abundance given a distance function,
detection data, site data, and area. This is called internally
by abundEstim. Users should use abundEstim to estimate
abundance.
estimateN(dfunc, detectionData, siteData, area = 1, bySite = FALSE)An estimate distance function (see dfuncEstim).
A data frame containing information on
detections. The minimum amount of information is the detection
distances and transect or point ID where each detection
occurred. (see Input data frames in help
for dfuncEstim).
A data frame containing information on the
transects or points surveyed (see dfuncEstim).
Total area of inference, study area size, or unit conversion.
See abundEstim.
A logical scalar indicating whether to compute site-level
estimates of abundance. The default (bySite=FALSE) returns only one
overall abundance estimate. See Value and Details.
If bySite is FALSE, a list containing the following components:
The input distance function.
Estimated abundance in the study area (if area >
1) or estimated density in the study area (if area = 1).
The number of detections (not individuals, unless all group sizes = 1) used in the estimate of abundance.
Total area of inference. Study area size
Effective strip width for line-transects, effective
radius for point-transects. Both derived from dfunc
Total number of transects for line-transects, total number of points for point-transects.
Total transect length. NULL for point-transects.
Average group size
The effective sampling distance at the site. For line- transects, this is ESW at the site. For points, this is EDR.
Average probability of detection at the site. If only site-level covariates appear in the distance function, pDetection is constant within a site. When detection-level covariates are present, pDetection is the average at the site.
The total number of individuals detected at a site.
Estimated abundance at the site. This is the sum of inflated group sizes at the site. i.e., each group size at the site is divided by its pDetection, and then summed.
Estimated density at the site. This is abundance at the site divided by the sampled area at the site. E.g., for line transects, this is abundance divided by \(2*w*length\). For points, this is abundance divided by \(pi*w^2\).
The effective area sampled at the site. This could be used as an offset in a subsequent linear model. For line transects, this is \(2*ESW*length\). For points, this is \(pi*EDR^2\).
If x is the data frame returned when bySite = TRUE,
the following is true:
For line transects, sum(x$abundance)*area/(2*w*sum(x$length))
is the estimate of abundance on the study area or the
abundance estimate when bySite = FALSE.
area*sum(x$density)/nrow(x) is the estimate of abundance
on the study area or the abundance estimate when bySite = FALSE.