Evolution imposes ‘speed limit’ on recovery after mass extinctions
It takes at least 10 million years for life to fully recover after a mass extinction, a speed limit for the recovery of species diversity that is well known among scientists. Explanations for this apparent rule have usually invoked environmental factors, but research led by The University of Texas at Austin links the lag to something different: evolution.
The recovery speed limit has been observed across the fossil record, from the “Great Dying” that wiped out nearly all ocean life 252 million years ago to the massive asteroid strike that killed all nonavian dinosaurs. The study, published in the journal Nature Ecology & Evolution, focused on the later example. It looks at how life recovered after Earth’s most recent mass extinction, which snuffed out most dinosaurs 66 million years ago. The asteroid impact that triggered the extinction is the only event in Earth’s history that brought about global change faster than present-day climate change, so the authors said the study could offer important insight on recovery from ongoing, human-caused extinction events.
The idea that evolution – specifically, how long it takes surviving species to evolve traits that help them fill open ecological niches or create new ones – could be behind the extinction recovery speed limit is a theory proposed 20 years ago. This study is the first to find evidence for it in the fossil record, the researchers said.
The team tracked recovery over time using fossils from a type of plankton called foraminifera, or forams. The researchers compared foram diversity with their physical complexity. They found that total complexity recovered before the number of species – a finding that suggests that a certain level of ecological complexity is needed before diversification can take off.
In other words, mass extinctions wipe out a storehouse of evolutionary innovations from eons past. The speed limit is related to the time it takes to build up a new inventory of traits that can produce new species at a rate comparable to before the extinction event.
The authors said that recovery from past extinctions offers a road map for what might come after the modern ongoing extinction, which is driven by climate change, habitat loss, invasive species and other factors.