Species-specific responses of Late Quaternary megafauna to climate and humans

Abstract

Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious. Here we use ancient DNA, species distribution models and the human fossil record to elucidate how climate and humans shaped the demographic history of woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. We show that climate has been a major driver of population change over the past 50,000 years. However, each species responds differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others, including Eurasian steppe bison and wild horse. We find no genetic signature or any distinctive range dynamics distinguishing extinct from surviving species, emphasizing the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change.

Figure 1

Modelled potential ranges of megafauna species at 42, 30, 21 and 6 ka BP. Ranges were modelled using palaeoclimatic data for temperature and precipitation and the megafauna fossil record. Range measurements were restricted to the regions for which fossils were used to build the models, rather than all potentially suitable Holarctic area.

Figure 2

Temporal changes in global genetic diversity and range size in horse, bison, reindeer and musk ox. X-axis is in calendar years; y-axis is the product of effective population size and generation time (N_e^*τ). Comparable estimates of associated range sizes (km²) are from Figure 1. The temporal span of the radiocarbon-dated samples used in each approach is shown as vertical lines below each panel and each line represents one dated individual.

Figure 3

Best-supported demographic models inferred by ABC model-selection for (a) Eurasia and (b) North America. Grey dots on the time axis indicate periods with range size estimates. Yellow dots indicate the periods of demographic increase or decline, which were tested against each other in the approach. White values inside coloured bars reflect support for the best-supported model (e.g. Eurasian woolly mammoth, increase at 26 ka BP). The intensity of increase or decline (e.g. x5) and effective population size at the time of the youngest sample (e.g. 10k individuals) are shown. We indicate in grey cases where multiple models received similar levels of support.

Figure 4

Spatial and temporal association between megafauna and Upper Palaeolithic humans in (a) Europe and (b) Siberia. Column graphs represent all known cultural occupations containing ≥ one of the six species, averaged over 2,000-year time bins. Open bars indicate the number of archaeofaunal sites, closed bars represent the frequency of each species in the binned assemblages. Area graphs show the fraction of megafauna surface area shared with humans at 1,000-year intervals, calculated from mean ± 1sd of latitude and longitude; data represented in Supplementary Figure S5.2. Graphs use coordinates of data associated with both direct and indirect dates.