We have done a variety of posts on the collapse of large settled communities, Empires, and the like. We have tried to expand beyond the typical Maya, Rome, discussions and bring up some the lesser known settled cultures that collapsed.
I have noticed a sub-theme within some sustainable style literature, often appearing to come with a communist anarchist style mindset that hunter gatherers do not have the same problems as agricultural communities.
That appears to be a gross overstatement. While it is true that hunter gatherer population does not grow as large on any given plot of land as do agricultural communities, the best evidence is that they also go through cyclical ups and downs, it is just that it is usually at a more localized level, so that unless you get some sort of weather extremes, it will not likely be over as large of an area, and the collapse will not involve as many people. In other words, if you have a situation comes where the holding capacity of the land, through a drought, becomes equal to 10 people per hectare, the hunter gather community with a density of 15 people have less distance to drop than the agriculturalists with 125 people per hectare. In the overcompensating downward thrust, one will lose about half its people, while the other will loss 95%.
As an example of a decentralized community collapsing:
Beginning at 10,000 B.C. California was occupied by foragers. Human densities were low and the people did not seem to be having much effect on the environment. For example, fur seals were breeding on the beaches a bit south of San Francisco and the pups would have been very susceptible to being taken by foragers. No boats were needed, just clubs. Yet for thousands of years the seals and the early Californians coexisted. It would appear that foragers were so few that they did not kill enough pups to reduce the herds to the point that the seals needed to abandon the mainland and breed only on offshore islands, as they do today. Since the pups were seasonal, this may have been an annual bottleneck in food supply that kept the human population down. However, as some point the bottleneck was overcome by finding a food that was available or storable at the time of year of the former bottleneck - probably acorns - and the people became sedentary collectors. Group sizes increased and more people began to take the fur seal pups. Around 2,000 B.C., the seals stopped rearing their pups on the mainland. Then the now much more numerous people began to exploit shellfish more intensely, allowing less time for them to mature between harvests. The average size of shells in the shell mounds declined over time. The human population along the California coast become more sedentary and began to act more like farmers, seriously impacting their environment. As I discuss later, it was about this time that there was an increase in warfare after this transformation.
His comment about being like farmers is a little unfortunate, because it is allowing the record keeping drive the story. There is considerable evidence of mass killings, with large amounts of game being wasted by less settled groups. But because they are less settled it is difficult to get a chronological record of their activities. We don't know what happened to the large game hunters numbers when all the easy prey in North America was killed. At the local level, there was likely a very rough transition, although a transition that would have been smoothed out a little as the climate was moderating and for the first time agriculture would have been possible.
When you look closely at what we can see of the prehistoric record, there appears to be much more of a continuom of behaviours between the two groups with the agriculturalists generally being able to build up larger populations, and thus suffering more dramtic swings in populatin. Swings that are also easier to record because of their sedentary life style.