Late Pleistocene proboscidean population dynamics in the North American Midcontinent

Abstract

Understanding megafaunal population dynamics is critical to testing and refining scenarios of how extinctions occurred during the terminal Pleistocene. Large-scale, collections-based, chronological and taphonomic analyses of midwestern Proboscidea suggest divergent population histories in mammoths and mastodons after the Last Glacial Maximum (LGM). Although extinction of both taxa occurred in the very late Bølling-Allerød (B-A) or early Younger Dryas (YD), Mammuthus is dominant during the LGM with a decreasing presence in the region until extirpation. Mammut americanum however, is absent during the LGM but becomes the dominant taxon during the subsequent B-A. Trace and physical evidence of large carnivores in post-LGM proboscidean assemblages is extremely rare, suggesting apex predators had minimal impact on mammoth and mastodon populations at this time. The ultimate mechanism(s) of extinction remain unclear; however, the wide geographical distribution of late Mammut and an increase in the frequency of multi-animal death assemblages is consistent with a large, destabilized population experiencing periodic boom-bust cycling at the end of the B-A. We suggest this pattern is due to the collapse of trophic controls on proboscidean populations prior to the LGM and a subsequent system-wide shift from top-down to bottom-up regulatory mechanisms in Proboscidea.

The overkill model and its impact on environmental research

“…However, it is more important for overkill to demonstrate that the lack of sites is a result of poor preservation of sites and remains. Interestingly, there are many paleontological sites from the Late Pleistocene with mammoth (Agenbroad, ; Widga et al., ) and other extinct megafauna (Meltzer, ). The higher proportion of remains in paleontological contexts compared to archeological ones suggests that megafaunal mortality may be better explained by natural rather than anthropogenic causes.…”

“…We assume that if these data were incorporated into the models comparing the impact of climate change versus human colonization, the results would be substantially different. Because of the variability in the timing of extinctions across taxa and in the evidence for interactions between humans and megafauna species, archeologists have argued that unraveling the mechanisms for the extinctions will require a “Gleasonian” approach, in which the extinction process is studied species by species (Grayson, ; Meltzer, ; for species examples, see Hill, Hill, & Widga, ; Widga et al., ).…”

“…However, it is more important for overkill to demonstrate that the lack of sites is a result of poor preservation of sites and remains. Interestingly, there are many paleontological sites from the Late Pleistocene with mammoth (Agenbroad, 2005;Widga et al, 2017) and other extinct megafauna (Meltzer, 2015).…”

“…Because of the variability in the timing of extinctions across taxa and in the evidence for interactions between humans and megafauna species, archeologists have argued that unraveling the mechanisms for the extinctions will require a "Gleasonian" approach, in which the extinction process is studied species by species (Grayson, 2007;Meltzer, 2015; for species examples, see Hill, Hill, & Widga, 2008;Widga et al, 2017).…”

Constituent databases and data stewards in the Neotoma Paleoecology Database: History, growth, and new directions

“…In recent years, many high-quality AMS radiocarbon dates on purified collagen have been published (e.g. Widga et al 2017), and many of these are from sites that are already in Neotoma. These new radiocarbon dates can now be added to existing or new geochronological datasets, and new age models can be built.…”