Morbid Monarchs

A new study by Semmens et al. finds that the monarch butterflies of eastern North America are likely to slide off the slippery slope of endangerment and over the cliff of extinction in the next 20 years. The extinction risk arises from rapidly falling monarch populations.

According to the study, monarch populations have declined 84% in the last 20 years. In the late 1990’s, the overwintering monarch population covered 13.90 hectares of forest; by the winter of 2014-2015, the overwintering population covered only 2.20 hectares of forest. This dramatic reduction in monarch population is caused by the continuing loss of milkweed habitats.

Monarchs lay their eggs on milkweed plants, and the developing larvae eat the plants when they emerge from the eggs. No milkweed, no eggs—no eggs, no larvae—no larvae, no monarchs. The milkweed habitats have decreased with the increasing adoption of herbicide-tolerant GMO corn and soybean crops. This chain of events is easy to follow: spray the fields with herbicides, the milkweeds die, and the monarchs have fewer places to reproduce.The study finds that the population loss is so precipitous that the eastern North American monarchs are likely to go over the extinction cliff in the next 20 years. Using statistical models (“a novel Bayesian multivariate auto-regressive state-space model,” if you really want to know), the researchers concluded that the monarchs have an 11-57% chance of “quasi-extinction” within the next 20 years.

“Quasi-extinction?” you ask, “What’s that?” Well, the report defines “quasi-extinction” as “the loss of a viable migratory population of monarchs in eastern North America.” It’s biologist-speak for “the point of no return”—the point at which there are not enough adult monarchs making whoopee to allow the population to survive—the point at which actual extinction is, as they say, merely a matter of time.

So, is fear of extinction irrational, when the data gives you grounds to expect it?

Citation: Semmens, B. X. et al. Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (Danaus plexippus). Sci. Rep. 6, 23265; doi: 10.1038/srep23265 (2016).

Read it here: http://www.nature.com/articles/srep23265#f1