Urban Development and Plant

¶ … Gitig, D. (2017). A farewell to kings? New ideas on the vanishing monarch butterflies. Ars Technica. April 30, 2017. Retrieved online: https://arstechnica.com/science/2017/04/a-migrating-butterfly-a-poisonous-plant-and-their-remarkable-coevolution/

In this article, Gitig (2017) provides an overview of recent research on monarch butterflies, focusing on the causes of their diminishing populations. Monarch butterflies feed almost exclusively on a plant called milkweed. Milkweed is disappearing rapidly due to urban development and other human activities. Therefore, the monarch butterflies have less to eat and this may be the direct cause for their dwindling numbers. In fact, adult monarch butterflies do not just feed on milkweed but also lay the next generation of eggs on the plant. The milkweed plant actually perceives the monarch as a parasite and emits latex to trap and kill the monarch caterpillars. Only about 10% of monarch eggs make it to become fully formed butterflies, according to the author. The most remarkable aspect of the monarch-milkweed relationship is that the surviving monarch caterpillars assimilate the toxic cardenolides from the milkweed latex by transforming those chemicals into color patterns in their butterfly wings. The chemical process is called aposematic coloration. The aposematic coloration gives the butterflies their unique appearance and also warns off potential predators, especially birds. Therefore, the monarchs benefit from the milkweed's defensive device. Gitig (2017) also discusses the potential causes for disappearing monarchs throughout their habitats in North America. Possible causes include habitat loss and drought conditions, but there is no one absolute cause for the dwindling numbers of monarchs.

There are several issues in this course that apply directly to this article. One issue is general ecology, as the article highlights the way different species interact with their environments. The relationship between the milkweed and the butterfly is not symbiotic, but rather parasitic in that the butterfly gains more from the milkweed than the other way around. The monarch butterfly is not a pollinator, though, and its role in the ecosystem is not directly addressed in this article. Another issue Gitig (2017) addresses is the evolution of defense systems in both plants and animals. The milkweed evolved the toxic latex to ward off the butterfly and other parasitic organisms, while the butterfly uses that same toxin to ward off birds and other predators. Finally, the article addresses conservation issues because the dwindling numbers of monarchs may be due to a number of human activities resulting either in the loss of milkweed or the loss of food sources for the adult butterflies. The article also tacitly addresses the importance of science literacy and the need to refrain from jumping to conclusions about cause and effect. Just because milkweed populations have dwindled does not mean that the loss of milkweed is the sole or even the most important cause of the reduced number of monarch butterflies. However, Doyle (2017) shows that recent experiments with replanting milkweed in urban locations has led to increased numbers of monarch butterflies in target areas.