India, Oct. 10 -- Invasive species often sneak in by accident. In New Caledonia, a French island territory in the South Pacific, the story was quite different. In 1870, 12 rusa deer arrived from Java, and legend says the governor of Java sent them as a diplomatic gift. According to a 2024 study in the European Journal of Wildlife Research by Alain Frantz and colleagues, the entire island population descends from those 12 founders. The team cites an estimate of between 250,000 and 370,000 deer, a figure from 2011.

The new home of the deer was very different from their home in Java. Native plants in New Caledonia evolved without the presence of grazing animals, including deer, according to a 2003 review in Pacific Conservation Biology. The...