Determinants of loss of mammal species during the Late Quaternary ‘megafauna’ extinctions: life history and ecology, but not body size

Abstract

Extinctions of megafauna species during the Late Quaternary dramatically reduced the global diversity of mammals. There is intense debate over the causes of these extinctions, especially regarding the extent to which humans were involved. Most previous analyses of this question have focused on chronologies of extinction and on the archaeological evidence for human-megafauna interaction. Here, I take an alternative approach: comparison of the biological traits of extinct species with those of survivors. I use this to demonstrate two general features of the selectivity of Late Quaternary mammal extinctions in Australia, Eurasia, the Americas and Madagascar. First, large size was not directly related to risk of extinction; rather, species with slow reproductive rates were at high risk regardless of their body size. This finding rejects the 'blitzkrieg' model of overkill, in which extinctions were completed during brief intervals of selective hunting of large-bodied prey. Second, species that survived despite having low reproductive rates typically occurred in closed habitats and many were arboreal or nocturnal. Such traits would have reduced their exposure to direct interaction with people. Therefore, although this analysis rejects blitzkrieg as a general scenario for the mammal megafauna extinctions, it is consistent with extinctions being due to interaction with human populations.

Megafauna biomass tradeoff as a driver of Quaternary and future extinctions

“…In parts of Australia (38), North America (39), and South America (40), the evidence for indirect human impacts includes sedimentary records of increasing fire frequency, potentially indicating widespread habitat alteration through human-set fires. The indirect or direct role of humans in the QME also is suggested by the observation that the main megafauna survivors had habitat preferences that would have kept them farthest from humans (41).…”

Reconsidering the Loss of Evolutionary History: How Does Non-random Extinction Prune the Tree-of-Life?

“…The size-selectivity of extinction risk is not unique to the current extinction crisis; past mass extinction events, such as that of the late Pleistocene, were also biased towards larger species (Martin 1967 ;Johnson 2002 ). During the late-Pleistocene -early-Holocene extinction event, there was a mass extinction of much of the mammalian megafauna, resulting in a loss of several complete ecological guilds and their predators (Cione et al 2003 ).…”

“…Size selectivity in extinction risk has been long-recognised (e.g. Pimm 1991 ;Lawton 1995 ;Pimm et al 1988 ;Cardillo and Bromham 2001 ;Johnson 2002 ), and there are many potential explanations. Large-sized mammals might be more extinction-prone because of generally lower average population densities (Damuth 1981 ), putting them at greater risk from stochastic population dynamics.…”

What caused extinction of the Pleistocene megafauna of Sahul?

“…Conceivably, this resulted from selective killing of big animals [17,18]. It is also possible that non-selective hunting differentially removed large species because of their low population growth rates and consequent sensitivity to small increases in mortality [15,19,20]. The main alternative to overkill is the idea that the megafauna disappeared because of climate change.…”