Saturday, June 23, 2012

We are at fault

Humans caused megafauna extinction in Australia.

As we weigh just how badly we intend to destroy the biosphere over the next few decades and centuries, a glance back at pre-history tells of some past indiscretions already on the books. The megafauna of Africa co-evolved with humans, and perhaps got to know their murderous ways in time to avoid them, at least enough to survive in part up to the present time in some spectacular examples- elephants, hippos, giraffes. Other continents had easily as dramatic a cast of megafauna, from giant sloths, lions, mastodons, to giant kangaroos, and moas. But on other continents, they lacked behavioral experience of humans and perhaps immune or other defenses, and disappeared rapidly after humans arrived.

The story has been documented on a correlation basis all over the world, from major continental invasions (North America and the Martin overkill hypothesis) to every island ever inhabited by humans. The magafauna of the Galapagos (i.e. its tortoises) are hanging on by a thread and only by conscious human reversal of our otherwise rapacious ways. The causes of extinction of mammoths in particular remains controversial, but I would bet far and away on humans being the ultimate cause- at least preventing their persistence in the refugia where they took shelter during previous warm periods.

A recent paper nails down the case of Australia in quite a bit more detail, showing the extremely close coincidence in time between the arrival of humans and various changes in the local ecology, including megafauna extinction. The researchers searched through layers of a prehistoric swamp for pollen, spores, charcoal, and carbon dates, to come up with a broad picture of the area.
"Australia's megafauna included twenty or more genera of giant marsupials, monotremes, birds, and reptiles, which were extinct by 40k years ago, soon after people colonized Australia"
A key part of the analysis is the spores of Sporormiella, a fungus that specializes on herbivore dung, serving as an index of herbivory by large animals. Unfortunately, they provide their graphs in two pieces, and to make them fit better, I rotated them flat. They track several ecological markers from 129k to 3k years ago.
Pollen abundance and other characteristics, by depth, from a pre-historic swamp in Australia, showing changes throughout, especially around the arrival of humans about 40k years ago (light gray vertical highlight on both graphs).
Green- rainforest flowering plants
Dark green- rainforest conifers and other gymnosperms
Red- Sclerophyll taxa= scrubby savannah- eucalypts, acacias, banksias, 
Yellow- Poaceae = grasses
Brown- Sporormiella indicate large herbivore presence.
Gray- charcoal from wild fires.

One can readily see that conditions dried out a bit at 70k years ago, well before humans arrived, reducing the rainforest angiosperm count. Sporormiella counts went up all the way until humans arrived at ~ 41k years ago. At that same time, pollen from grasses rises dramatically, as does charcoal. Rainforest pollen declines progressively, replaced by pollen from scrubby savannah plants.

The significance of this data set is in part that it corresponds to waht was climatically a quiet time. All that happened was that some humans learned how to build a boat to float across the Sunda Straight to Australia. The North American megafauna extinction is mixed up with the end of the ice age, but here in Australia, the climate was stable, so it easier to assign these widespread and dramatic landscape changes to the one thing that did change- the arrival of humans. It is highly reminiscent of how native Americans managed the prairies- by burning them frequently, finally banishing even scrubby plants in favor of all grasses all the time.

So, humans have been wreaking large-scale landscape damage and extinction for a very long time. We live in an impoverished world with only a glimmer of consciousness of what we have lost. The first European settlers in the Americas had unimagined bounty at their doorstep, which they then went on to systematically destroy in a typical tragedy of the commons. Fisheries are doing the same worldwide. But consciousness isn't enough, we need collective action.


"I have suggested to the monetary advisory committee for the FOMC that it is past time to try another tack: lower the payment for NOT extending credit. The power of monetary policy is to alter behavior in the world of credit. The 25-basis point payment, along with extremely low money market rates, enables banks to earn 1/4 percent a year from the Fed for doing nothing."

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