Forum: help

Unsure how to interpret BLUPs [ Reply ]
By: David Bradley on 2013-03-18 19:57

My apologies for my unfamiliarity with some statistical methods, particularly linear mixed effects models. This is my issue I was hoping to get some insight into solving:

I am trying to compare two populations birds that live in areas with different spring temperatures. For both populations, I have breeding records for the past 30 years, along with reliable measures of temperature. I have many birds that bred in multiple years, each year having different spring temperatures. I would like to know how best to measure the plasticity of breeding date in relation to temperature in each population.

Thus far I have been able to construct the LME model such that the fixed effects are:
temp - the population specific mean-centered mean temperature in May
site - the two populations
year - the breeding year

and the random effect is
ID - a unique band number on the females

# This is the model for the effect on egg laying date (date) in which I am interested in plasticity to temp
fm <- lmer(date ~ temp + site + year + (1 + temp|ID), REML=TRUE)
fm.blups <- ranef(fm)
fm.blups <- fm.blups[[1]]
write.csv(fm.blups, file = "fm.blups.csv")

I then want to know what the mean slope of temp in each population, as a measure of that population's plasticity.

Am I going wrong here?

Thanks for your thoughts,
David