Watching one of those National Geographic shows about food-chain competition on the African savana really got me thinking. Monster combat in the D&D world would certainly not be a "one and done" event.
If you are a cheatah on the savanna, you have mere minutes to feast on your kill before some tougher beasts arrive to take it from you. It can really go in cycles too, and depend on numbers, leading to a number of "chain battles".
The vulture pack might show up first, but then the dogs. Then the lions. Then the hyenas. Anywhere near water? Crocs are a sure bet to be on the prowl too. See what I mean? A bunch of different groups arrive at once and it turns into a total clusterfuck. A D&D world is going to be even more competitive and full of would-be alpha predators.
The rule book recommends a 1 in 6 chance of a random night time encounter, checked once per night. But how does that stack up against your experience, for example, camping in a forest? Better not have any food in your tent, because bears WILL sniff it out. How much more danger would you face in a magically-enhanced forest, full of magical uber-predators??? I'd say at least one encounter a night is guaranteed, especially if the party didn't take means to cloak their presence.
Anyway, after a deadly battle with animals or monsters in the wilderness, you can EXPECT the alpha predators to show up, it is GUARANTEED. Simply roll a 1d20 for rounds till they get there, and a 1d12 for type of monster. Roll 1d4 for how many times this will happen, i.e. how many different alpha predators will show up.
Alpha predator table
1 - Humanoid/barbarian hunting party
2 - Bear family (incl. werebears, Aurumvorax, etc.)
3 - giant Insects (incl. Thri-Kreen, Formians, etc.)
4 - Canine pack (dogs, wolves, werewolves, wolfweres, etc)
5 - Lion pride (incl. Wemics)
6 - Giant (incl. ogres, trolls, etc.)
7 - random monster
8 - Dragon
9 - giant Birds (incl. bats, Harpies, Vulchlings, etc)
11- giant Snake (incl. Behir, Boalisk, etc)
12 - giant Rats
Note, the alpha predator will probably just be interested in some food, i.e. dead meat at the scene. Intelligent alpha predators may also be interested in treasure, which means the PCs escape may be complicated....