sim.GRW {paleoTS}R Documentation

Simulate evolutionary time-series

Description

Simulate the evolution of a trait according to general random walk or stasis models.

Usage

sim.GRW(ns = 20, ms = 0, vs = 0.1, vp = 1, nn = rep(20, ns), tt = 1:ns)
sim.Stasis(ns = 20, theta = 0, omega = 0, vp = 1, nn = rep(20,ns), tt = 1:ns)

Arguments

ns number of samples in time-series
ms mean of the step distribution, random walk model
vs variance of the step distribution, random walk model
vp within-population trait variance
nn vector of the number of individuals in each sample
tt vector of sample ages, increases from oldest to youngest
theta evolutionary optimum, stasis model
omega evolutionary variance, stasis model

Details

See reference below for details on parameterization of the models.
Briefly, the general random walk model considers time in discrete steps. The duration of steps does not matter as long as many steps occur between sampled populations. At each time step, an evolutionary change is drawn at random from a distribution of possible evolutionary "steps." It turns out that the long-term dynamics of an evolving lineage depend only on the mean and variance of this step distribution. The former, mstep, determined the directionality in a sequence and the latter, vstep, determines its volatility.
The stasis model is based on the parameterization of Sheets and Mitchell (2001). Under this model, there is an evolutionary optimum, theta, with some amount of true variance, omega, around this optimum.

Value

A paleoTS object.

Author(s)

Gene Hunt

References

Hunt, G. 2006. Fitting and comparing models of phyletic evolution: random walks and beyond. Paleobiology 32:578–601.
Sheets, H. D., and C. E. Mitchell. 2001. Why the null matters: statistical tests, random walks and evolution. Genetica 112-113:105-125.

See Also

opt.GRW

Examples

 ## generate and plot two paleoTS objects
 y.rw <- sim.GRW(ns=20, ms=0.5, vs=0.1)  
 y.st <- sim.Stasis(ns=20)
 layout(1:2)
 plot(y.rw, col="red")
 plot(y.st, col="blue")
 layout(1)

[Package paleoTS version 0.3-1 Index]