The meercat is from Africa, and I remember seeing several at Adelaide Zoo, and there certainly were quite a few at the Singapore Zoo.
These little fellows who have an inbuilt need to have one of their males "on watch" at all times, still continue this ritual desp;ite being in captivity. I find it fascinating that they continue this behaviour all the time. One of the meercat men will stand on a high spot and look out for predators, just as he would have done in the wilds of Africa.
Every hour the guard changes. Another male will appear and stand near the other guard and they spend a few minute surveying the area, before the first one leaves. Every hour - day in, day out, they continue with this ritual.