Climate‐driven ecological stability as a globally shared cause of Late Quaternary megafaunal extinctions: the Plaids and Stripes Hypothesis

Abstract

Controversy persists about why so many large-bodied mammal species went extinct around the end of the last ice age. Resolving this is important for understanding extinction processes in general, for assessing the ecological roles of humans, and for conserving remaining megafaunal species, many of which are endangered today. Here we explore an integrative hypothesis that asserts that an underlying cause of Late Quaternary megafaunal extinctions was a fundamental shift in the spatio-temporal fabric of ecosystems worldwide. This shift was triggered by the loss of the millennial-scale climate fluctuations that were characteristic of the ice age but ceased approximately 11700 years ago on most continents. Under ice-age conditions, which prevailed for much of the preceding 2.6 Ma, these radical and rapid climate changes prevented many ecosystems from fully equilibrating with their contemporary climates. Instead of today's 'striped' world in which species' ranges have equilibrated with gradients of temperature, moisture, and seasonality, the ice-age world was a disequilibrial 'plaid' in which species' ranges shifted rapidly and repeatedly over time and space, rarely catching up with contemporary climate. In the transient ecosystems that resulted, certain physiological, anatomical, and ecological attributes shared by megafaunal species pre-adapted them for success. These traits included greater metabolic and locomotory efficiency, increased resistance to starvation, longer life spans, greater sensory ranges, and the ability to be nomadic or migratory. When the plaid world of the ice age ended, many of the advantages of being large were either lost or became disadvantages. For instance in a striped world, the low population densities and slow reproductive rates associated with large body size reduced the resiliency of megafaunal species to population bottlenecks. As the ice age ended, the downsides of being large in striped environments lowered the extinction thresholds of megafauna worldwide, which then increased the vulnerability of individual species to a variety of proximate threats they had previously tolerated, such as human predation, competition with other species, and habitat loss. For many megafaunal species, the plaid-to-stripes transition may have been near the base of a hierarchy of extinction causes whose relative importances varied geographically, temporally, and taxonomically.

Tracking late-Quaternary extinctions in interior Alaska using megaherbivore bone remains and dung fungal spores

“…It is unclear how isolation from the rest of North America would have impacted megaherbivore abundance. The lack of north–south exchange in North America may have limited long-distance dispersal, believed to be key to megaherbivore species survival in the region (Mann et al, 2015, 2019). The extinctions associated with the transition around 13 ka seen here represent the final wave of megafauna extinction in the area.…”

Caught in a bottleneck: Habitat loss for woolly mammoths in central North America and the ice‐free corridor during the last deglaciation

“…Disentangling the relative contributions of human populations and environmental changes to the late Quaternary extinctions has remained an active and sometimes contentious topic for decades (Barnosky et al., 2004; Mann et al., 2019; Surovell et al., 2016). The relative importance of anthropogenic and climatic drivers of extinction varied widely among megafaunal taxa (Lorenzen et al., 2011).…”

“…Barnosky et al., 2004; Surovell et al., 2016), with megafaunal species responding individualistically to the effects of climate change, habitat shifts, and growing human populations (Lorenzen et al., 2011). In temperate latitudes, regional habitat destabilization and rapid vegetation change during the last deglaciation may have contributed to the megafaunal extinctions in synergy with anthropogenic pressures (Blois & Hadly, 2009; Di Febbraro et al., 2017; Ficcarelli et al., 2003; Haynes, 2013; Mann et al., 2019; Nogués‐Bravo et al, 2010; Wang et al., 2020; Wroe et al., 2013). A key knowledge frontier is to better understand the particular interactions of climate, habitat, human pressures, and regional geography for each extinction.…”

Small mammals and paleovironmental context of the terminal pleistocene and early holocene human occupation of central Alaska

“…Paleoenvironmental archives in the middle Tanana Valley indicate that the terminal Pleistocene and early Holocene were characterized by a dynamic landscape (Mann et al, ). High rates of sediment input from aeolian or alluvial sources, frequent wildfires, megaherbivore grazing and trampling, as well as lagged dispersal of tree species all contributed to maintain the vegetation at early successional stages, with little soil development until 8,000 cal B.P.…”

“…Causes of ecological change in Beringia at the end of the Pleistocene ultimately relate to global climate change associated with the end of the Ice Age and the beginning of the current interglacial period (Mann, Groves, Gaglioti, & Shapiro, ). More proximate drivers of environmental change may have included regional climatic factors such as changes in atmospheric circulation and precipitation (Guthrie, ).…”