The analysis command allows you to run GRASS/shell commands across all your maps and then aggregate the results. Since the syntax can be tricky, this file documents some common use cases.
To work out the area of simulations.
./mdig.py -f area -t # (not -c because this has to be per replicate)
r.stats -c %0 | awk "BEGIN {notNULL = 0} /^[^*]/ {notNULL+=\$2} END {print notNULL}"
This can also be used to work out whether the population dies out, since you can then just check for zero.