How Climate Change Affects Butterflies

Excerpted from: Butterflies and Climate Change by Astrid Caldas

Climate change and butterflies Climate change is among the biggest challenges affecting pollinators, not because the Earth has not gone through drastic climate changes before, but because the changes happening now are compounding other, severe problems faced by the environment.

There are more species in danger of extinction than ever before, and climate change only adds to that number. Human activities have degraded the quality of the landscape so much that species and habitats may have less capacity to respond to environmental threats — including a changing climate. Therefore, it is essential that new, effective conservation plans include a climate adaptation component, either from early stages or as a later inclusion. That is especially true with butterflies.

Climate change will affect butterf ly species’ life cycles, flight times, essential interactions, and ultimately survival. Studies have already shown that butterflies are among the species that have responded the most to the effects of climate change.

Many butterflies possess an unusually heightened sensitivity to overly warm environs. Minute increases in temperature, imperceptible to humans, are of such significance to butterflies that they have triggered new patterns in the ancient process of metamorphosis and have even driven the creatures out of their native habitats.

Many studies have already shown that butterflies are among the species that have responded the most to climate change, usually in the form of northward or elevation range shifts. Federally listed as endangered, ‘Quino’ Variable Checkerspot is an example of a butterfly population that is directly threatened by climate change and habitat destruction.

Climate change will also affect species’ life cycles, flight times, essential interactions, and ultimately survival. There are many documented instances of disruption of essential interactions of butterflies with their food plants, most notably of Edith’s Checkerspots and the mismatched timing with their caterpillar food plants.

Life Cycle

The butterfly's reproductive development—and development across all life stages—is triggered by temperature. The climate affects the butterfly's body temperature, which helps it find a mate, increase fecundity and lay eggs.

A 2012 study by Viktoriia Radchuk and Camille Turlure showed that the number of eggs laid by the female butterflies, egg survival, and pupa survival increased with warming temperatures. However, because of a warmer winter, the overwintering larvae were more vulnerable to diseases and fungal infections, thereby decreasing larva survival. These results suggest that because temperature increases will negatively impact the overwintering stage of the butterfly life cycle, the most temperature-sensitive life stage, the overall population of butterflies will decrease significantly in the coming years due to climate change.

Flight Times

Climate change can also affect flight times in butterflies. Warmer temperatures will result in more generations of multiple-brooded species, but how this will affect egg-laying periods and other life traits that are determined by photoperiod (which is unchanged by climate change) is unknown. The researchers found that the start of the butterfly flight period advances on average by two days for each degree Fahrenheit increase in temperature (Boston University, Carol Polgar, 2013)

Food Availability

Butterflies who have specialized diets, meaning that they feed on one or a few plants, are more vulnerable to climate change because of fluctuations in their food. On the other hand, butterflies that have diverse diets are less likely to be affected.

For instance climate change threatens the Monarch’s food supply. When Milkweed senses warming temperatures, it increases the amount of cardenolide as a defense mechanism from the plant’s predators. This can be detrimental to Monarchs. Although they have a tolerance to the poison, they are not invincible to certain concentrations. The increased cardenolide levels in Milkweed present in warmer temperature poses a threat to both adult Monarchs and their larvae. It may become possible for the butterflies’ primary food source to become intolerably poisonous to them, a potentially disastrous outcome for the species.

Climate Change Impacts

“Climate” refers to the average conditions in a given location over time scales of decades to centuries. Year-to-year weather patterns average out to give a picture of what a typical or “climatological” year might look like. Over longer time scales, however – on the order of centuries to millennia – climate or “average” conditions in the Midwest have been very different than today.

18,000 years ago, when temperatures were an estimated 10 to 15° F cooler than they are today (Petit et al., 1999), the region was covered by a mile-thick ice sheet. By 10,000 years ago, the climate had warmed and the glaciers retreated, depositing layers of soil and rock debris that characterize the southern part of the region, and scouring out the many lakes and rocky shores typical of the more northern states.

Atmospheric levels of carbon dioxide are now higher than they have been at any time inat least the last 800,000 years. Average surface temperatures in the Northern Hemisphere have risen by 1.3° F over the past 150 years. It is very likely that most of the climate changes observed over the last 50 years have been caused by emissions of heattrapping or greenhouse gases from human activitie.

Further Reading on Climate Change:

 Climate Change Impacts On Wisconsin
 Climate Change Impacts On The Great Lakes
 Climate Change Impacts On Bees and Food Production
 Lake Michigan Warming: Climate Threats
 Growing Corn Is Changing The Climate
 How Climate Change Affects Wisconsin Winters

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