Why did large land mammals survive in Africa?

[Colibri]

@oliversarmy

Has Colinvaux’s “Why Big Fierce Animals are Rare” been discredited? I’m not looking for an argument, the book came out in the '70s, but his explanations seem as good as any.

What explanations specifically?

[EdwardLost]

@Lumpy

The destructive impact of elephants on farms is well documented. In India, elephant herds on stampede would occasionally destroy entire villages. Yes humans were predatory enough that elephants would move on if they had anywhere to go; but rather than starve to death while a field of yummy crops was just sitting there, a herd of three-ton animals would be rather difficult to deter with sharp sticks.

I’ll amend what I said; elephants and farmers in India obviously do compete. But I don’t think the animal’s size and fierceness explains how they’ve managed to survive. I think if the farmers had been able to farm all the land they would have eventually done so, and wiped out the elephants in the process. Instead, the fact that farmed land would become unproductive over time would keep the farmers on the move. The re-grown forest land would offer a refuge for the elephants, a place where they could feed and breed and avoid extinction. The two species would be continually pushing into each other’s territory, and sometimes elephants would win a village or two. But long term, I think the elephants owe their survival to abandoned, re-forested farmland.

[Dunkelheit]

@Colibri

However, given the nearly global extent of the extinctions, it is necessary to look for causes that apply to all areas. The extinction in Australia took place about 20,000 years before that in the Americas, that in Madagascar and New Zealand took place about 10,000 years later. There was no common climatic or other change to link these areas; the only commonality is that the extinction followed the arrival of modern humans.

Haven’t read the whole thread yet, please do forgive if I recover old ground here.

The three non-American examples you give are all islands, which would contribute significantly to the effects of invasion and predation on populations already limited in their range and their ability to escape both invading predators and the effects of other invading creatures on the local habitat. North America obviously doesn’t have quite the same problems due to its size, which is probably how some of the larger local species such as moose and elk were able to survive, because they had a broader distribution to start with, and were able to migrate to less inhabited areas such as Canada as the glaciers retreated.

This 2007 Discover Magazine article suggests that in North America there was a significant impact event during the ice age that would have had dire consequences for a lot of megafauna of the time, particularly those which were specifically adapted to an ice age climate: http://discovermagazine.com/2007/aug/the-great-american-extinction

Another thing to consider is that larger creatures often have longer gestation periods and smaller litters (only one or two offspring per pregnancy in many cases) that would also contribute to their difficulty in adapting to such rapid changes in environment or increases in predator populations. The megafauna of Africa have this trait as well, of course, but perhaps they were not as vulnerable to either environmental change or human predation for various reasons – equatorial Africa probably experienced relatively little change during the ice ages, at least not to the extent of breeding highly specialised ice age creatures like the Woolly Mammoth, for example, which would have been endangered by the retreat of the glaciers. Also, it seems to me that the remaining megafauna of Africa consists of relatively aggressive animals, such as elephants and rhinos, which it seems to me would go along with the notion that they have survived over time alongside humans by developing defenses against excessive predation.