Essay by: Christopher L. Hoving, Adaptation Specialist
This essay begins with two questions. How much should we spend to save a little blue butterfly? And how should climate change impact conservation and these kinds of spending decisions?
In this case, I am talking about the Karner blue butterfly. Listed by the federal government as endangered, this butterfly is also on Michigan’s list of threatened species. In fact, this butterfly is now confined to small populations in a very narrow, north-south range, including Wisconsin (the largest), Michigan (second largest), Ohio, New York and New Hampshire.
The map illustrates the historic range of the species. The circles represent historic Karner blue populations. The squares were the known populations when the map was created. However, two squares in northern Indiana, at the Indiana Dunes National Lakeshore, are now just circles. Those populations probably blinked out last year. They didn’t find any last year and only one male the year before that. Both the Illinois and Minnesota populations are now historic as well. We’re simply losing populations of this species.
One reason we have lost populations is because this species is so highly specialized. To begin with, lupine is the only plant that the larvae or caterpillars will eat. And in this range, native wild lupine grows only in one type of ecosystem type, oak savanna. The fact is, oak savannas are relatively rare and scattered. Karner blue butterflies are too small to move from one patch of savanna to a patch in the next county.
These savannas, especially temperate savannas, are the most globally endangered biome in the world. In Michigan, we’ve lost 99.98% of our oak savannas. And the remnants are usually a couple acres in size rather than landscapes of hundreds of acres. That is part of the reason this species is so endangered, because it is tied to this very fragile biome that has almost entirely disappeared due to fire suppression and conversion to agriculture.
One of the curious and kind of cool things about the Karner blue butterfly is its symbiotic relationship with certain ants. Ants actually take care of and
defend the caterpillars from predators. The caterpillars secrete a sugary substance as a reward to the ants. You often find Karner blue butterflies in fields that have lupine and also have these large ant colonies. The picture shows one of the ant hills that is about two feet across.
When talking of the Karner blue, we always show pictures of these cute little butterflies, but for most the butterfly’s life cycle, it is a caterpillar or an egg. The butterfly phase is relatively short, on average, just five to 10 days of its life span. We say “butterfly,” but they are really caterpillars for most of their lives.
If the Karner blue butterfly is to survive anywhere on earth, we need to preserve its habitat. As a employee of Michigan’s Department of Natural Resources, I helped direct the expenditure of over $100,000 in federal grants toward preserving and restoring oak savannas. The process included completing a number of prescribed burns over a five-year period, usually on private property. These burns essentially set back the process of succession such as scrub and tree growth. The result is a park-like setting halfway between open prairie and a closed canopy of trees.
Unfortunately, successful prescribed burns are expensive. You need to have specialized equipment and lots of support such as back up fire trucks on hand. Further, it can only be done in certain types of weather.
As a conservation agency we are constantly asking ourselves how to best invest conservation dollars. Money is tight, especially for endangered species, and we want to make sure we get what we pay for. Because Karner blue habitat responds well to management, and because Michigan is a stronghold for the species, it ranks relatively high for endangered species funding. However, more recently, we have begun to ask if this is money well-spent given the changing of Michigan’s climate. We need to begin assessing our natural resource management choices in relation to new climate regimes of coming decades. To answer that question, we have begun to ask how sensitive Karner blue butterflies and other wildlife species are to climate change.
The Karner blue butterfly is a butterfly that doesn’t like heat. When temperatures reach the low 90s to mid-90s, we begin to see mortality of the pupa, the stage between caterpillar and butterfly. During that critical life stage, they cannot do all the things an organism normally does to stay cool, like seeking shade or drinking more water. They are very sensitive to temperatures in the 90s.
Working with climatologists at the University of Wisconsin in Madison, we were able to obtain a downscaled model of the projected climate in the Great Lakes Region. The map shows the difference in the number of hot days (projected to be above 90 degrees), comparing the period of 1980-2000 to the period of 2040-2060. As shown by the orange color, models project an increase of between 21 and 28 days of temperatures exceeding 90 degrees by mid-century. You’re looking at 3 to 4 weeks more hot days each year on average, which is a lot.
This would suggest that those lethal temperatures for Karner blue butterflies will occur more often in the future in Michigan.
Which brings us back to the questions, how much should we spend to save this little butterfly?
Do we intervene to help the species move across the landscape and adapt to climate change? Do we leave it in place and hope that it evolves a response to a rapidly changing climate? And what should we invest to maintain its habitat in the meantime? Would any amount be good use of conservation dollars right now if the climate is going to be someplace else in the future?
I would say that we need to think of spending on species conservation in terms of an investment. During this time of climate change, we need to think of incremental investments over time. For example, Karner blue habitat can go about 10 years between prescribed burns. So Michigan made a 10-year investment in preserving the Karner blue butterfly at its current locations. Does it make sense to invest for another ten years at the same location, or should we move our investments further north? And how do we protect those investments here on landscapes further to the north for a species that has a very narrow north/south range? These are not easy questions, and they require that we think about species and places as dynamic, and that we think about conservation investments as time limited.
In the coming years, we are likely to encounter this issue with other species that are less endangered and have less narrow north/south ranges. However, Karner blue butterfly is a really good example of the kinds of investments and choices we will have to make. This little butterfly is a big illustration of the challenges climate change present to wildlife, wild places, natural resource managers, and to the citizens of Michigan.