By: Christopher Betancourt
On a cool, breezy day, you find yourself walking through the oyamel forests of Mexico. The firs are innumerable. The atmosphere is tranquil. The scenery is green. And then…a fiery orange. The trees are ablaze. Your heart skips a beat. A sudden forest fire? No. A trick of the mind? No. Should you approach? Yes, and you do. Before your very eyes, flames become wings. Butterflies. Monarch overwintering has begun. It is a breathtaking sight. Enjoy it while it lasts.
Beginning in the spring, monarchs enter into a series of breeding events and movements from the southern United States to the northern United States and Canada by summer. By fall, monarchs are ready to migrate nearly 5,000 km to overwinter in Mexico and the California coast. Monarchs are constantly in search of optimal conditions and dependent on consistent weather patterns, as these act as environmental cues for reproduction, migration, and hibernation (WWF). Such consistency no longer exists. This is echoed in a study that evaluated weather and climate conditions, in the form of hourly measurements of temperatures, the accompanying level of lethality, and future monarch distributions and/or projections. Results indicate that “suitable conditions at present overwintering sites will likely reduce in extent by 73–100% over coming decades” (Barve). One of the most concerning finds, in relation to the viability of Mexican overwintering areas, is that “suitable climate, protected area status, and forest show essentially no overlap by 2050” (Barve).
The presence of oyamel fir (Abies religiosa) forest cover plays a key role in monarch migration to Mexico. Aside from being native to Mexico, the oyamel fir is crucial for sheltering overwintering monarchs (Flores-Martínez). Such overwintering sites are protected by the Monarch Butterfly Biosphere Reserve (MBBR). While the MBBR prohibits logging activities within its core zones, “…illegal logging continues, including for commercial purposes, in fact constituting the single greatest current cause of deforestation” (Barve). During earlier periods, deforestation and habitat degradation were observed in the MBBR core zones; 731 hectares of land were lost in 2005-2007 (Flores-Martínez). The World Wildlife Fund (WWF) released a graph (Figure 1) in representation of total forest area occupied by monarch butterflies hibernating in Mexico, and there is a clear, downward trend.
When assessing the diet of the monarch butterfly, it feeds almost exclusively on milkweed species, within the genus Asclepias. For example, two of the species that monarchs feed on are Asclepias curassavica and Asclepias incarnata. While A. incarnata is a common, native species, A. curassavica is an exotic, commercially planted species (Faldyn). The invasive A. curassavica has recently exploded in popularity, offering monarchs a year-round source of food and, thus, less motive to migrate (Faldyn). In contrast, A. incarnata senesce during winter, leaving monarchs no choice except to migrate (Faldyn). Given the nature of A. curassavica, there exists widespread speculation on its potential to cause monarch populations to fall into an ecological trap. Should said environment experience alteration, those formerly reliable signals may no longer be viable, causing the organism to become trapped by their responses. Ecological traps have become increasingly prevalent, a fact which can be attributed to anthropogenic actions (Faldyn).
In response, an experiment was designed “to quantify the potential indirect effects of climate change on herbivore fitness and to gauge whether a warmer planet will result in the creation of an ecological trap…” (Faldyn). It was found that, under current climatic conditions, monarchs experienced heightened survival and mass when feeding on A. curassavica (Faldyn). However, under future conditions, such as those expected by 2080, “monarchs fared much worse on A. curassavica” (Faldyn). Milkweed produce cardenolides, which are chemical defenses that monarch larvae sequester, and use as a defense against predators, given that it makes them taste unpleasant. Such a study concluded that cardenolide concentrations increased with warmer temperatures, which in turn decreased adult survival and mass in monarchs (Faldyn). By progressively transitioning from beneficial to detrimental, A. curassavica represents a potential ecological trap under warmer climatic conditions: “Consequently, any changes…to milkweed chemistry due to global warming could have corresponding indirect effects on monarch performance” (Faldyn).
Putting aside milkweed, “monarch larvae exposed to constant, elevated temperatures experience increased mortality, longer developmental times, and weigh less as adults” (Faldyn). In addition, warmer temperatures decreased monarch forewing lengths, which can negatively impact flight potential: “Adult monarchs forewing lengths decreased by 2.5 mm, on average, when exposed to warmer temperatures…” (Faldyn). Such alterations have the potential to affect “butterfly flap‐glide efficiency, flight speed, and maneuverability,” giving rise to serious, lifelong complications (Faldyn). Taking milkweed into consideration, “…[monarch] survivorship was five times lower on A. curassavica at warmer temperatures than on A. curassavica at ambient temperatures…” (Faldyn). The recorded impacts of increased temperatures alone point toward monarchs as a particularly pertinent case of climate change effects.
The case of the monarch butterfly is just one of many that we can learn from. Monarchs prove that the repercussions of our routine actions are extensive and reverberate throughout the ecological realm, threatening a countless number of species in the process. Like the monarch, humanity has found itself caught in an ecological trap. We should be held accountable/take the fall for our own actions, not a species with expertise in the area we lack. The living, breathing knowledge within monarchs should be protected at all costs, studied, adopted, and applied. The survival of such knowledge is contingent on the survival of the species that provides it. Forging sustainable solutions at the expense of entire species is counterintuitive. If we paid as much attention to every species as we did the monarch, we would inherit a fortune of priceless understanding. Monarchs stand as tangible lessons, and it is our responsibility to learn from them before it is too late.
While the future of monarch populations remains unclear, “one of the world’s oldest, most resilient species could be decimated—and soon—by climate change” (Sieff). If we are even going to consider the possibility of talking about monarchs in “20, 30, 40 years,” a certain course of action must be taken (Sieff). What is needed, more than anything, is continued vigilance and support in the endeavor to protect monarchs. One thing is certain: If we lose monarch butterflies, we lose the battle with climate change.
- Barve, Narayani, et al. Climate-Change and Mass Mortality Events in Overwintering Monarch Butterflies. Sept. 2012, www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-34532012000300022&lng=en&tlng=en.
- Faldyn, Matthew J., et al. Climate Change and an Invasive, Tropical Milkweed: An Ecological Trap for Monarch Butterflies. 4 Apr. 2018, esajournals.onlinelibrary.wiley.com/doi/full/ 10.1002/ecy.2198.
- Flores-Martínez, José Juan, et al. “Policy Implementation Halts Deforestation in Winter Habitat of Monarch Butterflies in Mexico.” OUP Academic, Oxford University Press, 22 Apr. 2020, academic.oup.com/bioscience/article/70/6/449/5823920.
- Sieff, Kevin. Climate Change Is Playing Havoc with Mexico’s Monarch Butterfly Migration. 6 Jan. 2020, www.washingtonpost.com/world/the_americas/climate-change-is-playing-havoc-with-mexicos-monarch-butterfly-migration/2019/12/23/e60c1e0e-21ab-11ea-b034-de7dc2b5199b_story.html.
- WWF. Monarch Butterflies and Climate Change. www.worldwildlife.org/pages/monarch-butterflies-and-climate-change.