A paper just published in PNAS argues that since the flightless sea duck didn't got extinct until well into the Holocene humans probably didn't hunt megafauna to extinction. No, seriously.
Here's the title, and abstract:
****
The protracted Holocene extinction of California's flightless sea duck (Chendytes lawi) and its implications for the Pleistocene overkill hypothesis T. L. Jones, J. F. Porcasi, J. M. Erlandson, H. Dallas, Jr., T. A. Wake, an R. Schwaderer
Bones of the flightless sea duck (
Chendytes lawi) from 14 archaeological
sites along the California coast indicate that humans hunted
the species for at least 8,000 years before it was driven to
extinction. Direct
14C dates on
Chendytes bones show that the
duck was exploited on the southern California islands as early
as
11,150–10,280 calendar years B.P., and on the mainland
by at least 8,500 calendar years B.P. The youngest direct date
of 2,720–2,350 calendar years B.P., combined with the
absence of
Chendytes bones from hundreds of late Holocene sites,
suggests that the species was extinct by
2,400 years ago. Although
the extinction of
Chendytes clearly resulted from human overhunting,
its demise raises questions about the Pleistocene overkill model,
which suggests that megafauna were driven to extinction in a
blitzkrieg fashion by Native Americans
13,000 years ago. That
the extermination of
Chendytes was so protracted and archaeologically
visible suggests that, if the terminal Pleistocene megafauna
extinctions were primarily the result of human exploitation,
there should also be a long and readily detectable archaeological
record of their demise. The brief window now attributed to the
Clovis culture (
13,300–12,900 B.P.) seems inconsistent
with an overhunting event.
****
There is also an accompanying
commentary by Donald Grayson.
The authors have thoroughly documented an interesting relationship between human predation and this species of flightless duck. There seems little doubt that the duck was periodically or frequently preyed upon for millennia before it went extinct. They argue that the early inhabitants of the California coast were more technologically sophisticated than is generally acknowledged - they had some boats/canoes from which to hunt. What I don't understand is the lack of attention to ecology when they try to make the leap of connecting the relationship they document to Pleistocene extinctions in general. So maybe people had boats 12,000 years ago but I think its worth considering that there are some pretty fundamental differences between mammoths and ducks... (!!) and the particular island environments where most island extinctions took place are also different from the California coast. The colonists didn't bring rats, the environment was not as circumscribed as many islands and may have provided more natural refugia from human predation, the people may have had their main populations on the coast rather than on islands (in the california case), and they may have been at lower population densities.
Grayson's commentary is surprisingly even-handed. He seems more conservative with regard to the suggestion that this particular history of this particular species of flightless bird has general implications for our thinking of the loss of megafauna. But rather suggests that understanding the processes of extinction on a species by species basis tells us that there some important nuances that are often overlooked and that in many cases direct predation may not be the mechanism of extinction. Humans alter environments in lots of ways and it may be these indirect effects that are often detrimental. Rats and dogs and pigs all likely accelerated the rate of extinction in the case of Polynesian colonists.
Grayson and Jones et al (and lots of other archaeologists) frequently point out that the evidence for association between unambiguous signs of human activity and the remains of the extinct megafauna are rare in North America. And that is part of the point Jones et al are making. That this species has loads of direct associations with people and hence the extinction process is very visible. So why isn't it more visible for sloths and other really large critters that went extinct and should be very visible? If people were butchering these animals in a more expedient manner and not transporting bones to caves and rock shelters very often, then that could explain the lack of well preserved evidence. (I suppose). They also point out that the process of human mediated extinction seems to take a really long time in some cases, even islands, and yet for 35 genera across the entire continent of North America it was very rapid.
Good points in the article and in the commentary... would have liked to see more discussion of the ecological variables that alter the probability of extinction.
Best,
O
a spectacular evolutionary anomaly.
1:11 The extra-somatic adaptations, technological dominance, and success of our species in colonizing every terrestrial habitat have no parallel.2 Moreover, Homo sapiens accounts for about eight times as much biomass as do all other terrestrial wild vertebrates combined,3 an amount equivalent to the biomass of all 14,000+ species of ants,4 the most successful terrestrial invertebrates. Human societies are complex, with more specialized economic niches in the United States than the total number of mammalian species on the planet.5 While some might suggest that only post-industrial humans achieved stunning biological success, data suggest that humans living as hunter-gatherers would have attained a world population of more than 70 million individuals6 and a total biomass greater than that of any other large vertebrate on the planet if agriculture had not been repeatedly invented as they spread.
