A Late Pleistocene Demographic Winter Due to Global Warming?

With the ongoing climate crisis and global erosion of biodiversity, it is now of prime concern to better understand how ecosystems react to long-term climatic and anthropogenic stressors. In the late Pleistocene (~50,000-12,000 years ago), numerous species of mammalian megafauna (i.e. weight > 44 kg) experienced significant population declines ('bottlenecks'), or even total species extinction (e.g. woolly mammoths, cave bears), that coincided with major climatic changes and the growing presence of human populations in all continents. The development of new techniques, including paleogenetics and geochemistry, are beginning to help us understand these demographic collapses and their ecological consequences. However, the relative impacts of climatic and anthropogenic factors on these demographic changes remain debated in many cases. One reason for this arises from the complexity of assessing key aspects of past population dynamics (e.g. fertility rates) with currently available methods. However, recent studies have shown that the calcium (Ca) in the skeleton is isotopically different between conspecific individuals that reproduce and lactate to different extents. This discovery provides a unique opportunity to study reproduction behaviors and aspects of fertility rates through time based on fossil remains. PleistoDem will target a range of modern and fossil species, such as reindeers, mammoths and cave bears, from different locations in Europe and North America, representing the first largescale study using these techniques. Ca isotopic analyses will be integrated in a broader multi-proxy framework including stable light and strontium isotopic systems, in order to consider reproduction rates and behaviors within a high-resolution picture of past ecology, environment and mobility. This ground-breaking project will improve our understanding of Late Pleistocene ecological changes, which in turn will provide a solid base to anticipate and face future ecological changes.