Comparing big cats - differences/changes with time

[Pckts]

It's not that Jaguars dont prefer Tapir it's that they dont have a chance to hunt them in the north, caiman and capybara are everywhere, they are by far the most hunted prey a long with cattle during the wet season.
Tapir, anteaters, green anaconda, etc. Have higher numbers in the south, amazon and cerrado, in those areas you see more predation on said animals, except green anaconda which are much harder to see and less abundant in Jaguar land.
In north you will almost never see any of those animals I just named so documented hunts on them will be even less likely. But obviously they've learned to prefer capybara and Caiman since they're everywhere so it will only behoove the Jaguars to continue their aquatic transition.

Now in regards to morphological differences, we really cannot make that claim since to my knowledge there has been no study for it and the data is limited.
What we can say is that in the Pantanal the Jaguars are longer, heavier and have much larger skulls while the shoulder height doesn't really change.
The only two places this occurs are where there are an abundance of Caiman. The spines of Jaguars are very different from all other cats, they are more curved and arch almost towards the middle which is a similar trait to an Otter. 
When a cat grows a longer spine with a large curve without increasing shoulder height, that isn't a benefit for land but more so for the aquatic lifestyle. Like Otters who share the same traits, it helps them maneuver their bodies in water. Reply