Look at these maps.

http://swine.vet.uga.edu/nfsms/information/

I think it proves the obvious. Wild hogs existed 500-600 years in the far south without expanding their range much. Then some people decided to help them travel. In 1982, there were wild hogs in about 7 states and they had been given a lift to half of those. Fast forward to 2016, there are hogs in over 30 states. I seriously doubt the hogs grew pony tails and decided to just hit the road. LOL

JWAL,

You do bring up an interesting point. I wonder if anyone has done any research on how long it takes for an invasive species to adjust/balance to its new environment and how long it takes the new environment to adjust/balance to the invasive species. Assuming it will if given enough time.

All of my uncles that lived around Jay Fla in the 50s hunted hogs with catch dogs in the Escambia river swamp.

The distribution maps are nice EH but you really didn't address the question. I will ask it again. What kept the hog population from exploding for the 600 years( your number) that they were in existence in the areas they inhabited? According to current propaganda, there should be somewhere in the neighborhood of 400 billion hogs there now at their uncontrollable reproduction rate.

One point that is being overlooked is the fact that free-ranging (feral) hogs existed in many/most States. However, they were considered livestock and were 'owned' by the people with registered marks in those areas or were simply 'known' by the locals who ran woods hogs & cattle.
It was not until the Stock Laws started taking effect in the early 40's that people began having to fence them in. Then, in the mid to late 70's, deer hunting began really gaining popularity and have an economic impact. Along that time, the wildlife agencies began to take notice of the feral hogs and started to work towards making them fall under their domain. Here in AL, it was due to large landowners not having the power to prosecute poachers who were hunting their properties as they would claim to be gathering livestock. So, the feral hog became a Game Animal.
Then, the land-leasing craze of the 90's hit and property that had been long open to Public Use got gated and access more tightly controlled. As things progressed and the farming for wildlife got going, along with the implementation of clearcutting large areas of timber, the hogs really took hold with lots of places to hide and plenty of high quality groceries.
Nowadays, the trend is for wealthy individulals, families and/or investment groups to purchase large blocks of land and mange it for Recreational Use; I.e. Hunting. These properties are well-managed and have tightly restricted access. The hogs love em!!

So, that is my historically based opinion on the 'expansion' of feral hogs.
I am quite certain that many were relocated for recreational hunting by many varied user groups. But, land use has played a huge role as well. And, do not forget, their 'name' changed from livestock to Game Animals, too.

On populations, they fluctuate yearly and I know of many properties that used to hold large numbers of hogs that now have very few, or none. And, I also know of properties that never had any hogs that are now infested. The reasons are too numerous to list! But, they do stabilize given time. I would say that the densities are much lower than most estimate. This is due to the large areas hogs inhabit and their habit of waking roads leaving lots of sign. This makes people think there are far more than there really are.

So, that and about $1.50 will buy you a Coca Cola to drink while you mull it over!:)

You and I are saying the same thing. I don't think they explode on their own like many indicate.