Short answers, pulled from the story.
Assisted migration is the intentional establishment of plant or animal populations beyond the boundary of a species' historic range, so that species can track suitable habitats during a period of changing climate. The term first appeared in conservation biology publications in 2004, signifying a type of species translocation intended to reduce biodiversity losses caused by climate change.
The principal concern is that relocated species could become invasive in their new habitats and drive out native species. Researchers Mueller and Hellman reviewed 468 documented species invasions and found that only 14.7% occurred on the same continent where the species originated, and that fraction was dominated by fish and crustaceans rather than terrestrial species. Additional risks include disease spread, maladaptation to novel environmental conditions, and hybridization with closely related species already present in the recipient ecosystem.
Documented projects include the Florida torreya tree (Torreya taxifolia), which citizen group the Torreya Guardians began relocating northward as early as 2004; the western swamp tortoise (Pseudemydura umbrina) in Australia, whose first trial released 24 captive-raised juveniles in 2016; and a coupled project in Mexico involving the sacred fir Abies religiosa and Monarch butterfly overwintering habitat, with results reported in 2024. The Quino checkerspot butterfly (Euphydryas editha quino) and the American pika have been assessed for the approach but have not yet been formally relocated.
In June 2023, the U.S. Department of Interior modified the section 10(j) rule under the Endangered Species Act by removing the requirement that experimental populations be located within a species' historical range. This change effectively authorized assisted species migration for listed endangered or threatened plants and animals, allowing introduction to suitable habitats outside historical ranges to address climate-driven habitat loss.
Assisted migration specifically addresses species whose natural dispersal rates are too slow to keep pace with rapid human-caused climate change, targeting sites the species would naturally reach given more time, often adjacent to their current range. Invasive species introductions, by contrast, typically involve long-distance continent-to-continent or continent-to-island transport. Assisted migration practitioners consider it a small artificial boost to an otherwise natural process rather than an introduction to a wholly foreign ecosystem.
Alternatives include acclimatization and adaptation in place, assisted gene flow (AGF), stress conditioning, and hybridization. Assisted gene flow identifies naturally occurring genes that confer environmental tolerance and increases their transmission to offspring without inserting artificial genetic code; it is currently being tested on coral colonies of the Great Barrier Reef. One study found that some amphibians and reptiles could evolve sufficient heat tolerance within 100 years, though temperate trees may require thousands of years to achieve comparable adaptation.