Default disturbance function

Usage

def_disturb(x, species, disturb = NULL, ...)

x: population state distribution at time t
species: The species class object of interest to get mesh and RDIcoef values from. RDIcoef is a one line dataframe with RDI coefficient for one species.
disturb: Disturbance parameters. Highly depend on the disturbance impact parameters given to the species.
...: Default disturbance function does not require