Prevalent known and cryptic extinctions in the Pleistocene have conservation lessons for the next century
The growing field of conservation paleobiology provides a perspective on the range of species responses to global change beyond the limited scale of human observation. Given the challenges posed by future warming, ecologists are increasingly turning to the Quaternary paleorecord, which captures the last 2.588 million years of earth history, including the onset of global glacial-interglacial cycles. The Quaternary fossil record documents widespread shifts in species’ ranges and abundances in response to glacial-interglacial cycles, but it is typically thought that extinction and diversification were not important processes. This has resulted in the emerging paradigm in paleoecology that species may be more resilient than expected in the face of climate change. In contrast, our re-examination of the Quaternary fossil record indicates that the synergistic effects of climate change (both direct and indirect) and other landscape drivers put many species at greater risk than is currently appreciated.
We find that extinction was much more prevalent than has been previously appreciated, with respect to both documented extinctions and unidentified, or 'cryptic,' extinctions. Documented extinctions are more common than commonly thought due to previous temporal, regional and taxonomic biases. The recent reclassification of the start of the Quaternary from <2 ma to 2.588 ma BP, means that many extinctions previously identified as end-Pliocene actually occurred in the Pliestocene, during the onset of glacial-interglacial cycles and rapid climate change. Further, predominate attention paid to the last deglaciation misses a pulse of extinction in the mid-Pleistocene, at the onset of shifts in the periodicity and amplitude of glacial-interglacial cycles. Clade-based approaches tend to integrate taxa from different regions or habitat types, down-playing the mechanisms that drive extinction risk. Over the Pleistocene, cases of rapid speciation within habitats that are ephemeral relative to glacial-interglacial cycles provide evidence that a broader set of ‘cryptic’ extinctions have also occurred. Together, these data suggest that climate-associated extinctions have been much more common than previously appreciated. Consequently, the fossil record has yet to be fully marshaled to document extinction risk associated with climate change or to draw lessons from these extinctions for conservation challenges going forward.