Description Usage Arguments Details Value Author(s) References See Also Examples
Function to estimate the three fish movement parameters sigma_stat, sigma_mob and p describing the leptokurtic shape of fish dispersal kernels from field data.
1 |
data |
Single numeric vector of movement distances (field measurements) which should be used to estimate movement parameters. Here, only absolute movement distances are considered and differences in up- or downstream movement are ignored (symmetrical dispersal kernel assumed). |
start |
Named list of starting values used for the internal optimization process. If nothing is provided the 10% and 90% quantile of the input data are used as starting values for sigma_stat and sigma_mob and 0.67 is used as the starting value for p. |
ci |
Logical. If true confidence intervals (method=bca) are calculated. This feature is under current development and still unstable. The default value for |
rep |
Number of bootstrap replicates to calculate the confidence interval of the obtained parameters. The default value for |
conf |
Confidence interval used for parameter estimates. The default value for |
... |
do not use. |
fishmove.estimate
estimates the three fish movement parameters sigma_stat, sigma_mob and p describing the leptokurtic shape of fish dispersal kernels from field data. Here, a symmetrical dispersal kernel is assumed and only absolute movement distances are considered and differences in up- or downstream movement are ignored. The parameters are obtained by optimizing a double normal distribution with sigma_stat as dispersion (standard deviation) parameter for the first distribution, sigma_mob as dispersion (standard deviation) parameter for the second distribution, and p the weighing factor for the distributions (share of the stationary component):
F(x) = p * (1/(2*pi*sigma_stat^2)^(1/2))*e^(-(x-mu)^2/(2*pi*sigma_stat^2)) + (1-p) * (1/(2*pi*sigma_mob^2)^(1/2))*e^(-(x-mu)^2/(2*pi*sigma_mob^2))
The optimization is based on a maximum likelihood approach ("L-BFGS-B") using the underlying fitdistr() and optim() functions.
Under development: Based on non-parametric bootstrapping approach the 95%-confidence interval (method="bca") is calculated for the three extracted parameters. The default number of bootstrap replicates (rep
) is set to 100.
out |
If no confidence intervals are calculated (default), the return object is of class "fitdistr". The three estimated movement parameters sigma_stat (movement parameter of stationary component), sigma_mob (movement parameter of mobile component) and p (share of the stationary component) and their corresponding standard errors are provided. If bootstrapped confidence interval are calculated the fit, the lower and the upper bound of sigma_stat, sigma_mob and p are provided. |
Johannes Radinger
Radinger, J. and Wolter C. (2014) Patterns and predictors of fish dispersal in rivers. Fish and Fisheries. 15:456-473. DOI: http://dx.doi.org/10.1111/faf.12028.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | # Fictive fish movement data e.g. from a telemetry study (displacement distances)
set.seed(42)
fielddata <- c(rnorm(mean=0,sd=50,300),rnorm(mean=0,sd=700,200))
# extracting parameters using \code{fishmove.estimate}
parameters <- fishmove.estimate(fielddata)
parameters
# Plot
hist(fielddata,breaks=30,freq=FALSE)
# Definition of probability density function based on two superimposed normal distributions
# ddoublenorm <- function(x,sigma_stat,sigma_mob,p){
# dnorm(x,mean=0,sd=sigma_stat)*p+
# dnorm(x,mean=0,sd=sigma_mob)*(1-p)}
#x <- seq(min(fielddata),max(fielddata),length.out=1000)
#lines(x,
# ddoublenorm(x,
# parameters$estimate["sigma_stat"],
# parameters$estimate["sigma_mob"],
# parameters$estimate["p"]),
# col="red")
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