Repeated Measures using lmer

Question

I am trying to account for repeated measures in ecological data. The data are counts on exit times and numbers of individual bats leaving from roost locations over multiple years. Roosts were counted a varying number of times in different years, and also compared to other roosts. Roost is being used as a random variable. Here is an example of one of my models:

model1 <- lmer(min.after.sundn~distance.edge+repro.period+emerge.total+moon.phase+cloud.cover+moon.phase:cloud.cover+(1|tree), data=airport,REML=TRUE)

Explanation of variables:

min.after.sundn = continuous whole number measure of the number of minutes after sundown the first bat left the roost

distance.edge = continuous measure of distance

repro.period = categorical variable with 5 levels

emerge.total = continuous whole numbers

moon.phase = continuous fraction (0-1)

cloud cover = categorical with 5 levels

tree = roost locations that were monitored, dummy coded as numbers

My question is: Does the (1|tree) account for the repeated measures on its own? Or is there something ELSE I need to change?

I am in the process of dummy coding the different years of measures into the tree number so that tree counts in different years are not treated as repeated measures, which makes ecological sense since the dynamics of the population in a particular tree may change from year to year.

Any suggestions?

Answer 1

I think that you take the repeated measures into account adequately by including roost. Perhaps you could add a general effect of time if you didn't do that already. I don't think you should dummy code trees together with year so that each tree/year counts as different units with respect to the repeated measures, because there may be unmeasured variables that relate to a particular tree or the surroundings around that particular tree that affect the dependent variable. A favorable tree for a roost will probably be just as favorable in the next year and this might affect your outcome. I know very little about ecology, so it might make sense anyway, but it sounds suspect to my ears. :)