Reagarding Elephants in North Africa.
I am not 100% sure on that, but besides the decreasing effectiveness of elephants in the Mediterranean Area, I would say, they became extinct in that region, just like Lions, leopards and such. Mankind didn't treat the nature well, especially in this area. Further I could imagine the following reasons.
- Indian elephants trainers were much better, then their northafrican counterparts (pure speculation).
- terrain and climate in the mediterranean/northafrica area is not suited well for elphants, and became less so (one reason for extinction).
- Maybe they were used up by Carthago in the Punian wars, or in other words, the Romans killed them all, to avoid future uprisings in their new found Africa province.
- The mediterranean also has one big disadvantage moving those units, the sea. Even huge Carthagenian Triremes would have had some trouble carriing a dozen of those huge beasts. African Elephants are much bigger and wilder then Indian ones, and maybe much harder to tame.
- I have no idea in what terrain Indian elephants were most effective, but I imagine they did quite well on the open field and jungel areas, while mountainous battlefields would be hardly winable for an army that is elphant heavy.
- Regarding elephants in the very successful Hannibal campaign against Rome, I just can say, that they were not very important. They were for intimidation mainly, but didn't make it until roman heartland. In fact not more then 8 made it through the alps, the rest died quick of disease. Hannibals success came with the light numidian cavalry, and a lot of unhappy people all around the italian peninsula. Most Italian provinces quickly joined in Hannibals war against oppresive Rome. Hannibals final defeat was also to be found in deception and lack of serrenity in the Cartaghenian rule. So finally he was unable to pay all the mercenaries and Rome successfully bribed the Numidian riders, ....
To end this thoughts, most things said about the elephants in North-Africa is speculation, but I could well imagine it happening that way.
Edit: One more reason that one should not forget is "Ivory". Maybe the highly prized tusks of the elephants were a main reason for them getting extinct in Northafrica.