lefko3 (version 3.7.0)

sf_distrib: Test for overdispersion and zero inflation in size and fecundity

Description

Function sf_distrib takes a historically formatted vertical data as input and tests whether size and fecundity data are dispersed according to a Poisson distribution (where mean = variance), and whether the number of 0s exceeds expectations.

Usage

sf_distrib(
  data,
  size3 = NA,
  size2 = NA,
  obs3 = NA,
  fec = NA,
  repst = NA,
  zisize = TRUE,
  zifec = TRUE
)

Arguments

data

A historical vertical data file, which is a data frame of class hfvdata.

size3

The name or column number of the variable corresponding to size in occasion *t+1*.

size2

The name or column number of the variable corresponding to size in occasion *t*. This term is required for both size and fecundity tests.

obs3

The name or column number of the variable corresponding to observation status in occasion *t+1*. This should be used if observation status will be used as a vital rate to absorb states of size = 0.

fec

The name or column number of the variable corresponding to fecundity. The name of the variable should correspond to the proper occasion, either occasion *t* or occasion *t*-1.

repst

The name or column number of the variable corresponding to reproductive status in occasion *t*. Required if fecundity distribution will be tested.

zisize

A logical value indicating whether to conduct a test of zero inflation in size. Defaults to TRUE.

zifec

A logical value indicating whether to conduct a test of zero inflation in fecundity. Defaults to TRUE.

Value

Produces text describing the degree and significance of difference from expected dispersion, and the degree and significance of zero inflation. The tests are chi-squared score tests based on the expectations of mean = variance, and 0s as abundant as predicted by the value of lambda estimated from the dataset. See van der Broek (1995) for more details.

Notes

This function subsets the data in the same way as modelsearch() before testing underlying distributions, making the output much more appropriate than a simple analysis of size and fecundity variables in data.

The specific test used for overdispersion is a chi-squared test of the dispersion parameter estimated using a generalized linear model predicting the response given size in occasion *t*, under a quasi-Poisson distribution.

The specific test used for zero-inflation is the chi-squared test presented in van der Broek (1995).

Examples

# NOT RUN {
# Lathyrux example
data(lathyrus)

sizevector <- c(0, 4.6, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4, 5, 6, 7, 8,
  9)
stagevector <- c("Sd", "Sdl", "Dorm", "Sz1nr", "Sz2nr", "Sz3nr", "Sz4nr",
  "Sz5nr", "Sz6nr", "Sz7nr", "Sz8nr", "Sz9nr", "Sz1r", "Sz2r", "Sz3r",
  "Sz4r", "Sz5r", "Sz6r", "Sz7r", "Sz8r", "Sz9r")
repvector <- c(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1)
obsvector <- c(0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)
matvector <- c(0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)
immvector <- c(1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
propvector <- c(1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0)
indataset <- c(0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)
binvec <- c(0, 4.6, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5,
  0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5)

lathframeln <- sf_create(sizes = sizevector, stagenames = stagevector,
  repstatus = repvector, obsstatus = obsvector, matstatus = matvector,
  immstatus = immvector, indataset = indataset, binhalfwidth = binvec,
  propstatus = propvector)

lathvertln <- verticalize3(lathyrus, noyears = 4, firstyear = 1988,
  patchidcol = "SUBPLOT", individcol = "GENET", blocksize = 9,
  juvcol = "Seedling1988", sizeacol = "lnVol88", repstracol = "Intactseed88",
  fecacol = "Intactseed88", deadacol = "Dead1988",
  nonobsacol = "Dormant1988", stageassign = lathframeln, stagesize = "sizea",
  censorcol = "Missing1988", censorkeep = NA, NAas0 = TRUE, censor = TRUE)

lathvertln$feca2 <- round(lathvertln$feca2)
lathvertln$feca1 <- round(lathvertln$feca1)
lathvertln$feca3 <- round(lathvertln$feca3)

# The following will only test fecundity, since size is Gaussian.
# Zero-inflation will not be assessed in this example, since 0 values in
# fecundity have been excluded in the life history model.

sf_distrib(lathvertln, size2 = "sizea2", fec = "feca2",
  repst = "repstatus2", zifec = FALSE)

# Cypripedium example
rm(list=ls(all=TRUE))

data(cypdata)

sizevector <- c(0, 0, 0, 0, 0, 0, 1, 2.5, 4.5, 8, 17.5)
stagevector <- c("SD", "P1", "P2", "P3", "SL", "D", "XSm", "Sm", "Md", "Lg",
  "XLg")
repvector <- c(0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1)
obsvector <- c(0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1)
matvector <- c(0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1)
immvector <- c(0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0)
propvector <- c(1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
indataset <- c(0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1)
binvec <- c(0, 0, 0, 0, 0, 0.5, 0.5, 1, 1, 2.5, 7)

cypframe_raw <- sf_create(sizes = sizevector, stagenames = stagevector,
  repstatus = repvector, obsstatus = obsvector, matstatus = matvector,
  propstatus = propvector, immstatus = immvector, indataset = indataset,
  binhalfwidth = binvec)

cypraw_v1 <- verticalize3(data = cypdata, noyears = 6, firstyear = 2004,
  patchidcol = "patch", individcol = "plantid", blocksize = 4,
  sizeacol = "Inf2.04", sizebcol = "Inf.04", sizeccol = "Veg.04",
  repstracol = "Inf.04", repstrbcol = "Inf2.04", fecacol = "Pod.04",
  stageassign = cypframe_raw, stagesize = "sizeadded", NAas0 = TRUE,
  NRasRep = TRUE)

sf_distrib(cypraw_v1, size2 = "size2added", fec = "feca2",
  repst = "repstatus2", zisize = FALSE)

# }