Mammal communities after the megafaunal extinction

ICEA affiliate Rene Bobe contributes to a new paper on lessons to learn from the Pleistocene

Scientists from across Europe, the US and Canada, including ICEA affilate Rene Bobe, have contributed to a new analysis of the Late Pleistocene megafaunal extinction in North America in Science which looks for lessons for the modern world. Human activities have put extant large-bodied mammals at high risk of extinction, and their eventual loss may have severe ecological repercussions. For example, the loss of ecosystem engineers such as megaherbivores has the capacity to alter entire landscapes. Such human-mediated extinctions will have impacts lasting far beyond our lifetimes, making it important to examine long-term records of past extinctions to forecast the consequences of current biodiversity loss. A key example is the catastrophic and approximately synchronous extinction of large mammals, including mammoths and saber-toothed cats, at the end of the Late Pleistocene in North America. The rich and highly resolved Pleistocene and Holocene fossil record provides a unique opportunity to explore how extinction alters communities.

To understand the consequences of their demise for community assembly, the researchers tracked community structure through the end-Pleistocene megafaunal extinction in North America. They decomposed the effects of biotic and abiotic factors by analysing 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. The analysis suggests that these losses disrupted a network of species interactions that supported high levels of aggregation, leading to a modern fauna in which continent-wide species associations are now regulated more strongly by climate and dispersal limitation and are characterized increasingly by segregation. The paper finds that biotic mechanisms such as species interactions and range dynamics once played a measurable role in mammal community assembly by consistently affecting how species co-occurred on continental scales. Remaining species interactions among survivors likely take place opportunistically, on smaller scales, or within shorter timeframes. Overall, they found that biotic mechanisms now play a reduced role in species co-occurrences on a continental spatial scale, and this shift was most likely driven by the extinction of the Pleistocene megafauna.  Understanding past changes may help predict the community-level effects of the extinctions we are currently driving.