The evolution of wild species, adapting them to human management practices, can cause localised extinctions when those practices rapidly change. And in a new study published in Nature, Professors Michael C. Singer and Camille Parmesan have used more than 30 years of research to fully document an example of this process.
A large, isolated population of a North American butterfly evolved complete dependence on an introduced European weed to the point where the continued existence of the butterfly depended on the plant’s availability. The insects then became locally extinct when humans effectively eliminated that availability, confirming a prediction made by the same authors in a 1993 Nature paper.
Thus the advent of cattle ranching more than 100 years ago set an eco-evolutionary trap that the insects obligingly fell into, and the trap was sprung when humans suddenly removed the cattle, withdrawing their ‘gift’, and driving the butterflies to extinction.
As soon as the butterflies encountered the plantain, their caterpillars survived better on it than on their traditional host, Blue-Eyed Mary (Collinsia parviflora), causing the adults to evolve preference for laying eggs on the plantain. By the mid-2000s, they were 100% reliant on the plantain and the Collinsia had been abandoned.
However, within three years of the ranch’s cattle being removed due to financial pressures, the butterflies became locally extinct as the grasses around their favoured new host were no longer grazed, and the plantains became embedded in those grasses, cooling the micro-environment. The Collinsia was unaffected by removal of cattle, so if the butterflies had not evolved so rapidly in response to the introduction of the plantain, they would most likely have survived.
Around five years after the extinction, Edith’s checkerspots recolonized the meadow. Since they were all found feeding on Collinsia, the original host plant, scientists believe these colonists to be a new population, and that the lineage which had called the ranch home for several decades no longer exists. Paper. (paywall) – Michael C. Singer, Camille Parmesan. Lethal trap created by adaptive evolutionary response to an exotic resource. Nature, 2018; 557 (7704): 238 DOI: 10.1038/s41586-018-0074-6 More.
“Extinction” is put in scare quotes above, though not in the ScienceDaily release, because this event is correctly termed an “extirpation” from a region. The extirpation did not stop checkerspots from other regions from moving into the area five years later. This sort of thing may well be common in nature. “Extinction” should properly mean dead and gone, like the trilobite and the tyrannosaur.
A question arises: Given that butterflies often hybridize, some extinctions may not mean quite what we think.
Also, a surprising number of life forms we believe to be extinct turn out not to be (lazarus species).
The study authors suggest that similar events may be happening in Europe. We’d best e clear about what those events are, exactly.
See also: Sixth mass extinction, but no news on defining “species”?
Extinction (or maybe not): New Scientist offers five “Lazarus species”
Lazarus species: animals listed as extinct that turned up again.
In a meadow in America a group of butterflies have been drawn into a lethal evolutionary trap. This trap, set by humans, was abruptly sprung when people left the area, leading to a local extinction. Nature Video uses painted hands to tell the story of the Edith’s checkerspot butterfly. More.