Indeed, the demise of the megafauna is often packaged as an environmental morality tale (8, 9).
A recent series of articles, widely reported in the international media, have been heralded as a major breakthrough in this debate.
However, in both these models the unstated assumption was complete and unchanging prey naivety.
Recent field research has shown that both contemporary marsupial and eutherian prey populations can develop vigilance toward novel predators quite rapidly (21, 22), which raises the question: What would happen to the predictions of these models if this assumption was relaxed?
This is due to both a stimulation of the reproductive and natural survival rates to approach maximal levels (24, 25) and reductions in search efficiency.
The latter response reflects, in part, changed behavior of the animals such as increased wariness of humans (23) and a shift from diurnal to nocturnal grazing (26).
, which is published as supporting information on the PNAS web site, org, and Fig. To date, all overkill models assume prey off-take is described by a “type II functional response,” where = 1 (Alroy's assumption), our prediction of the probability of overkill (93%) actually exceeded Alroy's results (81%, based on the 37 scenarios in which he treated megafauna as an undifferentiated ecological unit, as we have done).