Reading a book on the cultural development of Brazil, I came away with a disquieting train of thought. The first aspect that became clear was that the native population was healthy and robust and remained so for most of the first century of contact in the contact coastal zone. It was reported on by many witnesses from all aspects. It is apparent that epidemic type depopulation would have been remarked upon. Yet these reports are missing.
That throws into question the whole idea of Indian depopulation by epidemic decimation. Particularly so as it mimics the experience shortly afterwards on the North American coast. There again we get reports of disease losses but nothing quite so catastrophic as endured by the remote tribes of the north west in the nineteenth century.
In Canada, the native cultures acquired a valuable trapping lifeway that secured their living in a way that was clearly superior to that abandoned and it is fair to say that the population actually thrived. In the USA this lifeway was quickly displaced and conflict reduced the viability of the original agrarian lifeway.
The point to all this was that the real epidemic was slave taking by the technically superior Europeans rather than disease in general.
While disease will usually kill off the very young and the very old with the exception of influenza allowing easy replenishment, slave trading preferentially takes the young adults with a full working life ahead of them. Rather obviously, if you constantly remove the breeding population to the coastal plantations, there will be no replenishment.
Population replenishment after a pass by an epidemic is surprisingly swift.
Recall that a mother is able to produce several offspring if there are plenty of resources available. The early reports from Brazil emphasize the richness of the indigenous food supply and the obvious excess of population that supported a culture of ritual cannibalism. This obviously acted to stabilize an expansive semi agrarian tribal system. It was not occasional and once slave taking began, almost certainly led to an acceleration of the population collapse.
This is also a disease that works well upcountry to supply manpower to the coast. Thus the Indians themselves did the bulk of the slave acquisition work.
Once a person was brought into slavery, their fecundity also collapsed because it cost the slave owner money to have children around and cared for when the value of a slave was cheap. It seems unlikely that slaves in Brazil maintained natural replacement. What replacement took place also likely took place at the hands of the slave owners producing hybrids even less susceptible to disease.
Thus the economic pressure of the cost of children and a low resale value would have passed the Indian population through a managed population collapse in which most of the survivors after several generations would be hybrids. In the end, slave trading replaced cannibalism.