priors_demo.RmdGenerating Priors based on Data and / or Expert knowledge:
Fitting priors to data (point estimates, all grass species in GLOPNET).
MLE Fit to glopnet Specific Leaf Area data
fit.dist function is in PEcAn.priors::fit.dist (See source code: https://github.com/PecanProject/pecan/blob/master/modules/priors/R/priors.R)
devtools::install_github("pecanproject/pecan/modules/priors")The fit.dist function takes a vector of point estimates (in this case 125 observations of Specific Leaf Area from GLOPNET database are stored in sladata.
First, it prints out the fits of a subset of distributions (the ‘f’ distribution could not be fit). Second, it prints the
dists = c('gamma', 'lognormal','weibull', 'f')
fit.dist(sladata, dists )The priorfig function visualizes the chosen prior (line), with its mean and 95%CI (dots) as well as the data used to generate the figure.
## priorfig(priordata = sladata,
## priordensity = slaprior,
## trait = 'SLA')
print(prior.figures$SLA)Fitting priors to data with uncertainty estimates (generating posterior predictive distribution of an unobserved C4 grass species based on values collected from many PFTs.
Vcmax data from Wullschleger (1993)
wullschleger.data <- read.csv('inst/extdata/wullschleger1993updated.csv')Classify Wullschleger Data into Functional Types
1. query functional types from BETY
This code is not run here - data are provided in .csv file below. This code requires connection to the BETYdb MySQL server.
wullschleger.species <- vecpaste(unique(wullschleger.data$AcceptedSymbol))
## load functional type data from BETY
con <- function() {query.bety.con(username = "bety", password = "bety",
host = "localhost", dbname = "bety")}
functional.data <- query.bety(paste("select distinct AcceptedSymbol, scientificname, GrowthHabit, Category from species where AcceptedSymbol in (", wullschleger.species, ") and GrowthHabit is not NULL and Category is not NULL;"), con())
write.csv(functional.data, 'inst/extdata/wullschleger_join_usdaplants.csv')Picking up with the Wullschleger dataset joined to USDA Plants functional type classifications …
functional.data <- read.csv('inst/extdata/wullschleger_join_usdaplants.csv')
subshrubs <- rownames(wullschleger.data) %in% c(grep('Shrub',wullschleger.data$GrowthHabit), grep('Subshrub', wullschleger.data$GrowthHabit))
########## 2. Merge functional type information into Wullschleger data
wullschleger.data <- merge(wullschleger.data, functional.data, by = 'AcceptedSymbol')
########## 3. Classify by functional type
## grass: any Graminoid Monocot
grass <- with(wullschleger.data, GrowthHabit == 'Graminoid' & Category == 'Monocot')
## forbs/herbs = forb
forb <- with(wullschleger.data, GrowthHabit == 'Forb/herb' | GrowthHabit == 'Vine, Forb/herb')
## woody = Shrubs, Subshrubs or Trees, add category to a few with missing information,
woody <- with(wullschleger.data, scientificname %in% c('Acacia ligulata', 'Acacia mangium', 'Arbutus unedo', 'Eucalyptus pauciflora', 'Malus', 'Salix') | rownames(wullschleger.data) %in% c(grep('Shrub', GrowthHabit), grep('Subshrub', GrowthHabit), grep('Tree', GrowthHabit)))
## gymnosperms
gymnosperm <- wullschleger.data$Category == 'Gymnosperm'
## ambiguous is both woody and herbaceous, will drop
ambiguous <- wullschleger.data$GrowthHabit %in% c("Subshrub, Shrub, Forb/herb, Tree", "Tree, Subshrub, Shrub", "Tree, Shrub, Subshrub, Forb/herb", "Subshrub, Forb/herb")
wullschleger.data$functional.type[grass] <- 1
wullschleger.data$functional.type[forb] <- 3
wullschleger.data$functional.type[woody & !gymnosperm] <- 4
wullschleger.data$functional.type[woody & gymnosperm] <- 5
wullschleger.data <- subset(wullschleger.data, !ambiguous)
############# Estimating SE and n ##################################
##verr, jerr: the "asymptotic" errors for Vcmax, Jmax using SAS nlim
##vucl,vlcl,jlcl,jucl: are upper and lower confidence limits of 95%CI
##Calculate SD as (1/2 the 95%CI)/1.96
wullschleger.data$vsd <- (wullschleger.data$vucl-wullschleger.data$vlcl)/(2*1.96)
##Calculate effective N as (SE/SD)^2 + 1
wullschleger.data$neff <- (wullschleger.data$vse/wullschleger.data$vsd)^2 + 1
wullschleger.data$se <- sqrt(wullschleger.data$vsd*sqrt(wullschleger.data$neff))
## recode species to numeric
species <- unique(wullschleger.data$scientificname)
sp <- rep(NA, nrow(wullschleger.data))
for(i in seq(species)){
sp[wullschleger.data$scientificname == species[i]] <- i
}
############# Scale values to 25C ##################################
wullschleger.data$corrected.vcmax <- arrhenius.scaling(wullschleger.data$vcmax,
old.temp = wullschleger.data$temp,
new.temp = 25)
############# Create data.frame for JAGS model ##################################
wullschleger.data <- data.frame(Y = wullschleger.data$corrected.vcmax,
obs.prec = 1 / (sqrt(wullschleger.data$neff) * wullschleger.data$se),
sp = sp,
ft = wullschleger.data$functional.type,
n = wullschleger.data$neff)
## Summarize data by species
wullschleger.vcmax <- ddply(wullschleger.data,
.(sp),
summarise,
Y = mean(Y),
obs.prec = 1/sqrt(sum((1/obs.prec)^2)),
ft = mean(ft), # identity
n = sum(n)) [,-1]Add data from C4 species
Few measurements of Vcmax for C4 species were available. ###### Miscanthus: Wang D, Maughan MW, Sun J, Feng X, Miguez FE, Lee DK, Dietze MC, 2011. Impact of canopy nitrogen allocation on growth and photosynthesis of miscanthus (Miscanthus x giganteus). Oecologia, in press
dwang.vcmax <- c(19.73, 40.35, 33.02, 21.28, 31.45, 27.83, 9.69, 15.99, 18.88, 11.45, 15.81, 27.61, 13, 21.25, 22.01, 10.37, 12.37, 22.8, 12.24, 15.85, 21.93, 23.48, 31.51, 23.16, 18.55, 17.06, 20.27, 30.41)
dwang.vcmax <- data.frame(Y = mean(dwang.vcmax),
obs.prec = 1/sd(dwang.vcmax),
ft = 2, #C4 Grass
n = length(dwang.vcmax))Muhlenbergia glomerata
Kubien and Sage 2004. Low-temperature photosynthetic performance of a C4 grass and a co-occurring C3 grass native to high latitudes. Plant, Cell & Environment DOI: 10.1111/j.1365-3040.2004.01196.x
Data from figure 5 in Kubien and Sage (2004), average across plants grown at 14/10 degrees and 26/22 degrees
kubien.vcmax <- data.frame(Y = mean(23.4, 24.8),
obs.prec = 1/sqrt(2.6^2 + 2.5^2),
n = 8,
ft = 2) Zea Mays (Corn)
Massad, Tuzet, Bethenod 2007. The effect of temperature on C4-type leaf photosynthesis parameters. Plant, Cell & Environment 30(9) 1191-1204. DOI: 10.1111/j.1365-3040.2007.01691.x
data from fig 6a
massad.vcmax.data <- data.frame(vcmax = c(17.1, 17.2, 17.6, 18, 18.3, 18.5, 20.4, 22.9, 22.9, 21.9, 21.8, 22.7, 22.3, 25.3, 24.4, 25.5, 25.5, 24.9, 31.2, 30.8, 31.6, 31.7, 32.5, 34.1, 34.2, 33.9, 35.4, 36, 36, 37.5, 38.2, 38.1, 37.4, 37.7, 25.2, 25.5),
temp = c(20.5, 24.6, 21, 19, 21.9, 15, 19.6, 14.3, 20.8, 23.4, 24.8, 25.9, 24.1, 22.8, 27.9, 31.7, 35.5, 39.3, 37.9, 42.4, 41.5, 48.7, 33.3, 33.3, 31.5, 39.1, 38.8, 43.3, 50, 38.4, 35.7, 34.4, 31.9, 33.9, 32.1, 33.7))
massad.vcmax <- with(massad.vcmax.data, arrhenius.scaling(old.temp = temp,
new.temp = 25,
observed.value = vcmax))
massad.vcmax <- data.frame(Y = mean(massad.vcmax),
obs.prec = 1/(sd(massad.vcmax)),
n = length(massad.vcmax),
ft = 2)
##### Combine all data sets
all.vcmax.data <- rbind(wullschleger.vcmax,
dwang.vcmax,
## xfeng.vcmax,
kubien.vcmax,
massad.vcmax)take a look at the raw data by functional type:
qplot(data = all.vcmax.data, x = factor(ft), y = Y, geom = 'boxplot')Add unobserved C4 species so JAGS calculates posterior predictive distribution
vcmax.data <- rbind(all.vcmax.data,
data.frame(Y = NA, obs.prec = NA, ft = 2, n = 1))Write and Run Meta-analysis
writeLines(con = "vcmax.prior.bug",
text = "model{
for (k in 1:length(Y)){
Y[k] ~ dnorm(beta.ft[ft[k]], tau.y[k])T(0,)
tau.y[k] <- prec.y*n[k]
u1[k] <- n[k]/2
u2[k] <- n[k]/(2*prec.y)
obs.prec[k] ~ dgamma(u1[k], u2[k])
}
for (f in 1:5){
beta.ft[f] ~ dnorm(0, tau.ft)
}
tau.ft ~ dgamma(0.1, 0.1)
prec.y ~ dgamma(0.1, 0.1)
sd.y <- 1 / sqrt(prec.y)
## estimating posterior predictive for new C4 species
pi.pavi <- Y[length(Y)]
diff <- beta.ft[1] - beta.ft[2]
}")
j.model <- jags.model(file = "vcmax.prior.bug",
data = vcmax.data,
n.adapt = 500,
n.chains = 4,
inits = inits)
mcmc.object <- coda.samples(model = j.model, variable.names = c('pi.pavi', 'beta.ft', 'diff'),
n.iter = iter)
mcmc.o <- window(mcmc.object, start = iter/2, thin = 10)
pi.pavi <- data.frame(vcmax = unlist(mcmc.o[,'pi.pavi']))
vcmax.dist <- fit.dist(pi.pavi, n = sum(!is.na(vcmax.data$Y)))
prior.dists <- rbind(prior.dists, 'Vcmax' = vcmax.dist)
vcmax.density <- with(vcmax.dist, prior.density(distribution, a, b), xlim = c(0,50))
######### Vcmax Prior Plot
vcmax.c4 <- all.vcmax.data$ft == 2
vcmax.data <- transform(all.vcmax.data, mean = Y, se = 1/(sqrt(n) * obs.prec))[,c('ft', 'mean', 'se')]
#vcmax.mean <- all.vcmax.data$Y[!c4,]
#vcmax.se <- with(all.vcmax.data[!c4,], 1/(sqrt(n) * obs.prec))#[reorder]
#c4.mean <- all.vcmax.data$Y)[c4]
#c4.se <- with(all.vcmax.data, 1 / (sqrt(n) * obs.prec) )[c4]
prior.figures[['Vcmax']] <-
priorfig(priordensity = vcmax.density,
trait = 'Vcmax',
xlim = range(c(0, max(vcmax.data$mean)))) +
geom_point(data = subset(vcmax.data, ft != 2),
aes(x=mean, y = (sum(vcmax.c4) + 1:sum(!vcmax.c4))/3000), color = 'grey60') +
geom_segment(data = subset(vcmax.data, ft != 2),
aes(x = mean - se, xend = mean + se,
y = (sum(vcmax.c4) + 1:sum(!vcmax.c4))/3000,
yend = (sum(vcmax.c4) + 1:sum(!vcmax.c4))/3000),
color = 'grey60') +
## darker color for C4 grasses
geom_point(data = subset(vcmax.data, ft == 2),
aes(x=mean, y = 1:sum(vcmax.c4)/2000), size = 3) +
geom_segment(data = subset(vcmax.data, ft == 2),
aes(x = mean - se, xend = mean + se,
y = 1:sum(vcmax.c4)/2000, yend = 1:sum(vcmax.c4)/2000))
print(prior.figures[['Vcmax']])Other Examples / Approaches
Examples
- Estimating priors for the DALEC model in [models/dalec/inst/DALEC_priors.R](https://github.com/PecanProject/pecan/blob/master/models/dalec/inst/DALEC_priors.R
Package rriskDistributions
The rriskDistributions useful for estimating priors …
as well as individual functions for each distribution such as get.<somedist>.par that provide nice diagnostic plots (e.g. compare chosen points to cdf) for example, to compute the parameters of a Gamma distribution that fits a median of 2.5 and has a 95%CI of [1, 10]:
library(rriskDistributions)
get.gamma.par(p = c(0.025, 0.50, 0.975), q = c(1, 2.5, 10), tol = 0.1)The function fit.pecr provides a GUI to explore the fits of a range of distributions, e.g.:
fit.perc(p = c(0.1, 0.5, 0.9), q = c(30, 60, 90), tolConv = 0.1)produces this:
image of rriskDistributions example that uses GUI