Role of Homo Sapiens in Megafauna extinctions

Wherever man went, he destroyed. When it came to Nature, he played God too. Man has the distinction of being the greatest destroyer of Nature when compared to any other species that inhabited this earth. Wherever we go we decide what should live and what should not.

Ground  Sloth

 In America there were giant sloths, lions, mammoths and mastodons. Australia had eight foot long horned turtle, and a 25 foot lizard. All of them disappeared. What are the reasons for this recent megafauna extinctions? Paul Martin, a scientist at the University of Arizona developed the theory of "Pleistocene overkill", which held that as man spread out from Africa and colonized new continents, he killed off the great beasts that he found there. The dates seem to fit. Man arrived in Australia 48,000 to 50,000 years ago, the megafauna disappeared 46000 years ago. Man crossed into Tasmania from Australia through a land bridge 43000 years ago and the big animals in Tasmania disappeared 41000 years ago. In North America the megafauna seems to have disappeared around 13000 years ago at around the date of the first human settlements. Our earliest ancestors would, quite reasonably, have gone after the biggest animals they could to feed their families and kill the biggest predators to cut down on competition and attacks. Mix in human ingenuity, climatic changes, and hundreds and thousands of years and you soon get a land denuded of megafauna.

Glyptodons - enormous armored mammals 

Lets see what Man has done when he first set foot on some inhabited mass of land. Ever since the present Maoris ancestors arrived in New Zealand from some Polynesian islands somewhere in 1250-1300 it has lost 51 species of birds, three of frogs, three of lizards and one of freshwater fish. This was brought about by a combination of hunting, deforestation and the Polynesian rats that the Maoris brought with them.  Nearly all of the world's isolated islands could furnish similar examples of extinctions occurring shortly after the arrival of Homo sapiens. For some reason megafauna in Africa and Southern Asia was spared during the Pleistocene extinction. Some scientists have blamed climatic changes for such mass extinctions, but recent research has shown that climate change were minimal during this time.

Throughout earth's history extinctions have been the norm. Around 99% of all creatures that have ever lived have disappered from this planet. Hardly any of the species that are around now existed 100 m. years ago. It is also unlikely that many of today's species will be around in another 100m years.

What is the impact of humanity on biodiversity? In order to assess this fact, we need to know as to how many species there are on this planet. The most widely used estimate now is 8.7m species excluding bacteria and archaea. It is an established fact that species continue to die out naturally in the natural scheme of things. This is known as the "background rate of extinction" This rate has been calculated as one per million species years - if there were a million species on the planet, one would go extinct every year, and if there was one species on the planet, it would go extinct in a million years. There are 10000 species of birds. If the background extinction rate was the only force at work, one bird species would go extinct every century. A study of some Pacific islands inhabited by Polynesian migrants revealed that they wiped out 50% to 90% of the bird life. On an average these Polynesians were wiping out a species or two per year, that is at least a hundred times more than the background extinction rate.

In Australia, researchers argue that newly arrived humans hunted the animals to extinction, with the reduced grazing pressure causing an increase in the fuel load and fire intensity. This prompted the disappearance of rainforests and the expansion of eucalypt-dominated forests. Scientists suggest that protracted hunting by humans, perhaps over 10,000 years or more, was the probably number one extinction driver, but environmental changes happening at the time probably exacerbated the situation. This has led them to conclude that one-factor explanations for the Pleistocene extinctions are very likely overly simplistic in Australia.

Some scientists fear that unless people think that mass extinctions are imminent, they will not do anything about it. However, since the 1970's humanity has made far greater efforts to protect other species, mainly thanks to the change of attitudes brought about by greater awareness.

Source:

Extinction-Dead as a Moa, The Economist Sept 14th 2013.