Additive effects of climate change and human hunting explain population decline and extinction in cave bears

Abstract

Cave bears (Ursus spelaeus) are an iconic component of the European late Quaternary Ice Age megafauna. Recent demographic analyses based on cave bear mtDNA sequences and refined radiocarbon dating indicate that cave bear population size and genetic diversity started to decline some 50 kilo years ago (kya). Hence, neither the coldest phase of the last glaciation (started some 24 kya), nor the colonization of Europe by Palaeolithic hunters (started some 45 kya) coincides with the beginning of population decline. Here, we reconstructed cave bear climatic niche evolution through time. Then, we performed spatially explicit population viability analyses to assess cave bear demographics through time in response to climatic changes, human effects on bear survival and their combination. We found that climate change was responsible for a 10‐fold decrease in cave bear population size after 40 kya. However, climate change on its own could not explain U. spelaeus extinction at 24 kya. Additional negative effects consistent with human population expansion are required to explain both U. spelaeus' retreat from eastern Europe since 40 kya and its final extinction.

Three-dimensional dental topography and feeding ecology in the extinct cave bear

“…Although hypothesizing on the specific vegetal resource that cave bears were specialized to feed on is tempting, our results indicate that cave bears were specialized to feed upon tough vegetal resources of the high-alpine biome, which supports the climate-driven hypothesis to explain their extinction at the beginning of the Last Glacial Maximum when the primary productivity that the cave bear fed upon was dramatically lowered [3][4][5].…”

“…Some authors propose that cave bears were adapted to feed exclusively on vegetal resources from 100 000 to 20 000 years ago [2], without evidence of a dietary shift towards omnivory at a time of lowered vegetation productivity during the Last Glacial Maximum [3]. Both the lack of dietary flexibility and possible human competition are proposed to be critical factors in explaining the extinction of cave bears [4,5]. Recently, Pérez-Ramos et al [6] demonstrated that large paranasal sinuses were likely selected in cave bears to overcome longer hibernation periods, but the sinuses also compromised the skulls biomechanically.…”

The role of habitat fragmentation in Pleistocene megafauna extinction in Eurasia

“…Mitochondrial DNA and population demographics suggest the cave bear Ursus spelaeus suffered a dramatic population decline starting at 50 ka (Mondanaro et al 2019). The same rapid decline in exactly the same time interval pertains to the Eurasian populations of cave lion Panthera leo spelaea (Stuart and Lister 2011), and cave hyena Crocuta crocuta spelaea (Stuart and Lister 2014).…”

“…In fact, the best radiometric estimates for the extinction date of Homo neanderthalensis (at 40 ka, Higham et al 2014) the giant rhino Elasmotherium sibiricum (Kosintsev et al 2019) the camel Camelus knoblochi , the giant deer Sinomegaceros yabei , the narrow‐nosed rhino Stephanorhinus hemitoechus , the antelope Spiroceros kiakhtensis and the Asian straight‐tusked elephant Palaeoloxodon naumanni are all concentrated in the narrow 45–37 ka interval (Stuart and Lister 2012). Mitochondrial DNA and population demographics suggest the cave bear Ursus spelaeus suffered a dramatic population decline starting at 50 ka (Mondanaro et al 2019). The same rapid decline in exactly the same time interval pertains to the Eurasian populations of cave lion Panthera leo spelaea (Stuart and Lister 2011), and cave hyena Crocuta crocuta spelaea (Stuart and Lister 2014).…”

“…Most extinct megafauna persisted in the Mediterranean area, and in the far East, before extinction, abandoning northernmost habitats first (e.g. cave hyaena, Stuart and Lister 2014; cave lion, Stuart and Lister 2011; cave bear, Mondanaro et al 2019; Neanderthals, Fabre et al 2009). In fact, the presence of glacial refugia and cryptic northern refugia may have only increased habitat patchiness for the Eurasian megafauna as a whole (Hewitt 2000, Bhagwat and Willis 2008) and testifies to this progressive retreat from the north.…”