We thank Tijmen Jan Moser, one anonymous associate editor, and two
anonymous reviewers for helpful suggestions, which improved the
quality of the paper. This work is partly supported by National
Natural Science Foundation of China (Grant No. 41522404 and 41430322)
and National Key Research and Development Program of China (Grant
No. 2016YFC0600505). All results are reproducible in the Madagascar
open-source software environment (Fomel et al., 2013).