unmarked (version 0.8-1)

colext: Fit the colonization-extinction model.

Description

Estimate parameters of the colonization-extinction model, including covariate-dependent rates and detection process.

Usage

colext(psiformula= ~1, gammaformula =  ~ 1, epsilonformula = ~ 1,
pformula = ~ 1, data, starts, B=0, method="BFGS", control=list(),
    se=TRUE)

Arguments

psiformula

Right-hand sided formula for the initial probability of occupancy at each site.

gammaformula

Right-hand sided formula for colonization probability.

epsilonformula

Right-hand sided formula for extinction probability.

pformula

Right-hand sided formula for detection probability.

data

unmarkedMultFrame object that supplies the data (see unmarkedMultFrame).

starts

optionally, initial values for parameters in the optimization.

B

number of bootstrap interations (the default 0 indicates no bootstrapping).

method

Optimization method used by optim.

control

Other arguments passed to optim.

se

logical specifying whether or not to compute standard errors.

Value

• unmarkedFitColExt object describing model fit.

Details

This function fits the colonization-extinction model of MacKenzie et al (2003). The colonization and extinction rates can be modeled with covariates that vary yearly at each site using a logit link. These covariates are supplied by special unmarkedMultFrame yearlySiteCovs slot. These parameters are specified using the gammaformula and epsilonformula arguments. The initial probability of occupancy is modeled by covariates specified in the psiformula.

The conditional detection rate can also be modeled as a function of covariates that vary at the secondary sampling period (ie., repeat visits). These covariates are specified by the first part of the formula argument and the data is supplied via the usual obsCovs slot.

See unmarkedMultFrame and formatMult for more information on supplying the data.

References

MacKenzie, D.I. et al. (2002) Estimating Site Occupancy Rates When Detection Probabilities Are Less Than One. Ecology, 83(8), 2248-2255.

MacKenzie, D. I. et al. (2006) Occupancy Estimation and Modeling. Amsterdam: Academic Press. Royle, J. A. and R. Dorazio. (2008).

Examples

data(frogs)
umf <- formatMult(masspcru)
obsCovs(umf) <- scale(obsCovs(umf))
## constant transition rates
(fm <- colext(psiformula = ~ 1,
gammaformula = ~ 1,
epsilonformula = ~ 1,
pformula = ~ JulianDate + I(JulianDate^2), umf, control = list(trace=1, maxit=1e4)))

## try yearly transition rates
yearlySiteCovs(umf) <- data.frame(year = factor(rep(1:7, numSites(umf))))
(fm.yearly <- colext(psiformula = ~ 1,
gammaformula = ~ year,
epsilonformula = ~ year,
pformula = ~ JulianDate + I(JulianDate^2), umf, 
	control = list(trace=1, maxit=1e4)))