grizzly: Population sizes of grizzly bears in Yellowstone from...

Description Usage Format Details Source References Examples

Description

Estimated number of adult female grizzly bears in the Greater Yellowstone population from 1959-1997.

Usage

1

Format

A data frame with 39 observations on the following 2 variables.

year

Year of census

N

Estimated number of female grizzlies

Details

The grizzly bear data set is used in count based PVAs in chapter 3 in Morris and Doak 2002.

Source

Table 3.1 in Morris and Doak 2002. Original data from Eberhardt et al. 1986 and Haroldson 1999. Additional details on the Interagency Grizzly Bear Study Team is available at http://nrmsc.usgs.gov/research/igbst-home.htm.

References

Morris, W. F., and D. F. Doak. 2002. Quantitative conservation biology: Theory and practice of population viability analysis. Sinauer, Sunderland, Massachusetts, USA.

Examples

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data(grizzly)
attach(grizzly)
## plot like Fig 3.6 (p. 66)
plot(year, N, type='o', pch=16, las=1, xlab="Year", 
ylab="Adult females", main="Yellowstone grizzly bears")
## calcualte  log(Nt+1/Nt)
nt<-length(N)  ## number transitions
logN<-log(N[-1]/N[-nt])
## Mean and var
c(mean=mean(logN), var=var(logN))
## or using linear regression
## transformation for unequal variances (p. 68)
x<-sqrt(year[-1]-year[-length(year)])
y<-logN/x
mod<-lm(y~0 + x )
## plot like Fig 3.7
plot(x,y, xlim=c(0,1.2), ylim=c(-.3,.3), pch=16, las=1,
xlab=expression((t[t+1]-t[i])^{1/2}),
ylab=expression(log(N[t+1]/N[t]) / (t[t+1]-t[i])^{1/2}) ,
main=expression(paste("Estimating ", mu, " and ", sigma^2, " using regression")))
abline(mod)
## MEAN (slope)
mu<- coef(mod)
## VAR (mean square in analysis of variance table)
sig2<-anova(mod)[["Mean Sq"]][2] 
c(mean= mu , var= sig2)
## Confidence interval for mean  (page 72)
confint(mod,1)
## Confidence interval for sigma 2  (equation 3.13)
df1<-length(logN)-1
df1*sig2 /qchisq(c(.975, .025), df= df1)
## test for outliers using dffits (p.74)
dffits(mod)[dffits(mod)> 2*sqrt(1/38) ]
## plot like  fig 3.11
plot(N[-nt], logN, pch=16, xlim=c(20,100), ylim=c(-.3, .3),las=1,
xlab="Number of females in year T",
ylab=expression(log(N[t+1]/N[t])),
main="Grizzly log population growth rates")
cor(N[-nt], logN) 
abline(lm(logN ~ N[-nt]), lty=3 )
detach(grizzly)

popbio documentation built on May 4, 2018, 1:04 a.m.