LAUSR

Extinction leads to restructuring By most accounts, human activities are resulting in Earth's sixth major extinction event, and large-bodied mammals are among those at greatest risk. Loss of such vital ecosystem components can have substantial impacts on the structure and function of ecological systems, yet fully understanding these effects is challenging. Tóth et al. looked at the loss of large-bodied mammals in the Pleistocene epoch to identify potential community assembly effects. They found that the demise of large mammals led to a restructuring and a shift from biotic to abiotic drivers of community structure. Understanding past changes may help predict the community-level effects of the extinctions we are currently driving. Science, this issue p. 1305 Loss of large mammals during the Pleistocene led to community restructuring. Large mammals are at high risk of extinction globally. To understand the consequences of their demise for community assembly, we tracked community structure through the end-Pleistocene megafaunal extinction in North America. We decomposed the effects of biotic and abiotic factors by analyzing co-occurrence within the mutual ranges of species pairs. Although shifting climate drove an increase in niche overlap, co-occurrence decreased, signaling shifts in biotic interactions. Furthermore, the effect of abiotic factors on co-occurrence remained constant over time while the effect of biotic factors decreased. Biotic factors apparently played a key role in continental-scale community assembly before the extinctions. Specifically, large mammals likely promoted co-occurrence in the Pleistocene, and their loss contributed to the modern assembly pattern in which co-occurrence frequently falls below random expectations.