Because extinction is forever, conservation biologists have always shared Andrew Marvell’s urgency: But at my back I always hear Time's wingèd chariot hurrying near. Conservation biology as a term and an interdisciplinary science is only 39 years old yet already it is reframed. Established by American biologists in 1978, conservation biology began due to concern over loss of tropical habitats and associated biodiversity (a term created eight years later). Our primary aim was to encourage restoration and preservation of healthy ecosystems, habitats, and species populations. From the beginning, biologists called it a “discipline with a deadline” — we needed to act before our subjects vanished. It was about putting things back together and protecting them so we didn’t need to write obituaries.
Conservation biology is rooted in ideas from the late 1700’s about preserving nature, although the term “conservation” wasn’t used until the late 1800’s. Initially, it mostly referred to hanging onto economically important natural resources (timber, soil, fish, game, minerals) although it soon expanded to include forests, wildlife, and watersheds. The first conservation law was in Britain in 1869. In the U.S., the earliest conservation law passed in 1891. John Muir founded the Sierra Club in 1892. Barely more than a century later, conservation has acquired new meaning and more urgency — that wingèd chariot is bashing into our heels and running faster won’t help.
As global warming has accelerated and become an implacable force of change, conservation biology has also changed. Biologists consider the degree of adaptation and resilience a species or habitat possesses; we look at how well they can deal with change. In truth, that’s always been the case as nothing alive is preserved in it’s original state, but now change has taken on new powers. How can we protect species and habitats when the habitats themselves either need to move or be dismantled by climate change consequences? When the change is that the habitats move geographically, but all pieces might not move together? When the species may make adjustments we didn’t realize were possible?
We need to know where a species’ best ecological conditions will exist in a future we are only beginning to describe and we aren’t sure when or how it will happen.
Conservation biologists hypothesize environmental scenes of the future based on data and models provided by climatologists. Because the climate’s changes interact with all the other processes of nature and human actions, we develop models that imagine future conditions in specific locales and across landscapes. Often, these models focus on only a few species within that landscape.
How climate change might affect monarch butterflies and their habitats is one such model. It examines possible changes and how a species must adapt or face extinction.1
As overwintering monarchs hang out in fir trees in Mexico’s Sierra Madre Oriental mountains, do they wonder if their travel arrangements for spring will work out? They expect to fly north, stopping as needed to lay eggs on milkweed plants before dying, confident their offspring will resume the annual migration to their summer ranges where they will find ample milkweed and nectar plants. For monarch butterflies, there’s always been world enough and time. But is this true in 2017? What will happen in 2055? What kind of adaptations must monarchs make for changing climate conditions?
Scientists know that monarch breeding depends on having the proper temperature and precipitation ranges. If temperatures are a little too high or too low, monarch larvae grow more slowly and fewer survive. Temps above 42oC (108oF) are lethal, while at temperatures below 12oC (54oF) larvae don’t develop. Using the temperatures at which monarch larvae grow normally and actual observations of monarch breeding, researchers mapped the current suitable breeding habitat of monarchs at different times of the year.
Below are the areas currently with suitable breeding conditions (usually) in April (Map 1) and in July (Map 2). Red is good breeding conditions. Grey is okay, not lethal but marginal and larval growth will be slower. And white is horrible, no successful breeding. All the information discussed here is specific to the eastern subpopulation that overwinters in Mexico.
The above maps were validated using citizen science data of observed monarch breeding from the Monarch Larva Monitoring Project. (You can join and be part of this effort.)
Then, using modeling data from climatologists, researchers identified where these same temperature and precipitation conditions will exist in 2055 if we get our act together fast and keep carbon dioxide (CO2) increases to 0.5 percent per year (less than the current rate of increase). This is considered the best case scenerio. If CO2 increases at a higher rate, the habitat shifts further north. There’s only so much north to go. Thus, just as habitats shift upslope to cooler areas and run out of mountain, we can run out of northern territory.
On the maps below, pink shows the new areas not currently used by monarchs that are expected to offer optimal suitable temperature and precipitation conditions for monarch breeding in 2055. Grey/red shows where the monarchs are now. Grey areas have high temperatures only marginally suitable for monarchs right now (thus horrible in 2055). Red areas have optimal temps right now but presumably will be the marginal zone in 2055.
In 2055, by June not much optimal monarch breeding habitat will be in the U.S.
By August 2055, monarch breeding habitat almost reaches the Hudson Bay and there’s suitable habitat in Newfoundland!
Will the monarchs overwintering in Mexico be able to fly far enough north to reach suitable 2055 breeding habitat? Will milkweed grow there? Now, monarchs can breed in the area shown on Map 1 as they move north and areas on Map 2 during the summer. But in 2055, they may need to fly much further, as shown on Maps 4, 5, and 6.
Below are the maps for right now in July (Map 1, left) and in August 2055 (Map 6, right). Although the maps and scale are not the same, it’s obvious that much territory currently supporting monarchs won’t have suitable habitat in 38 years. New suitable habitat will be mostly in Canada in areas now considered horrible.
We don’t know what will happen to monarchs between now and 2055. Many more issues affect the population such as the ability of their overwintering habitat in Mexico (and California) to shelter them. But we know what monarchs are doing this year. People are reporting oddities in Mexico’s overwintering sites and in the U.S.2
This winter in Mexico, monarchs were more active than normal, flying around, nectaring, and even mating during the winter instead of spending most of the days tightly clustered in fir trees. This was due to unusually warm sunny days and, perhaps in some cases, due to 2016 storm damage and illegal logging that opened light gaps and reduced the canopy cover causing monarchs to shift somewhat to other nearby portions of the Biosphere that were less damaged. In winter, monarchs are in diapause, a state of suspended development of their reproductive organs driven, in part, by temperature. Biologists wondered if their unusual activity implied an early end to diapause, and if they would depelete their stored lipids, reducing their ability to migrate in spring.
Migration north began at the normal time in the first half of March, but more monarchs remained in the overwintering sites than usual. On April 2nd, a large percent of the population was still in Sierra Chincua portion of the Monarch Biosphere. On April 10th, thousands of monarchs were seen flying in the El Rosario portion, a sight local people called “strange.”
Migrating monarchs reached south central Texas a bit later than usual, after March 12th. More butterflies arrived, and both remigrants (those who traveled south in autumn, overwintered in Mexico, and migrated north again in spring) and the new generation (born in the U.S. this spring from eggs laid by remigrating females) kept moving north slowly. Weather conditions seemed to stall migrants in Oklahoma on April 7th. The butterflies searched out all the milkweed just sprouting and laid eggs everywhere. People were concerned there wouldn’t be enough food for all the larvae when the eggs hatched.
A monarch mama usually is fastidious about spreading out eggs, laying a single egg on a young leaf, with only a few eggs widely spread out on a plant. She distributes the eggs so each larva will have enough to eat right where hatched. When there isn’t enough milkweed available, “egg dumping” occurs and the monarch lays too many eggs on one plant, often in a small area that isn’t likely to have enough milkweed to feed all the larvae. (See example in photo to the right and note that tiny sprout on the left also has an egg attached.)
On April 9th, the leading edge of spring migration advanced 150 to 200 miles in two days (presumably due to strong northerly winds). People north of Oklahoma saw their first monarch earlier than ever before, as reported by Journey North. Here’s one observation from April 8th in St Joseph, Missouri.
...tattered female laying eggs on newly emerged swamp milkweed (egg dumping) flew looking for more milkweed but kept returning to the one area with 5 tiny sprouts, probably a remigrant who came from Mexico all the way north.
And from April 16th in Zion, Illinois.
...first monarchs seen . . . earliest ever seen by reporter but no milkweed yet seen and few nectar plants….
The maps below are where the monarchs have been observed and reported to Journey North by April 18th in 2017, 2012, and 2000. NOTE: the number of dots only relates to how many observations were submitted and doesn’t necessarily reflect the actual monarch population. More people participate in citizen science monitoring projects now. (You can report sightings to Journey North and also join a new citizen science project from Monarch Watch intended to help fill in knowledge gaps related to monarch use areas. Another website for reporting butterflies also has an app: eButterfly. Butterflies, milkweed, nectar plants and many other organisms can be reported to iNaturalist. You can upload photos and ask for identification help, too.)
This year, monarchs now are well into the northern Great Lakes area (and some were reported from Pelee Point in Ontario, Canada).
Five years ago, the monarchs had barely reached the Great Lake states by April 18th.
Seventeen years ago, the monarchs were even further south, barely into Kentucky.
The general trend of reports I’ve read for this year north of Texas/Oklahoma are claiming earlier than usual monarch sightings (sometimes earliest ever); no or only small milkweed sprouts present when the monarchs are looking to lay eggs; and frequent ocurrences of egg dumping, often on small sprouts. My information in this article mingles research data (required breeding habitat conditions, maps, and climate change scenerios) and anecdotes from experienced citizen scientists (2017 reports). This year’s observations are not the full story across the monarch’s range. But it’s notable that people are not seeing the synchronous arrival of monarchs with suitable milkweed growth. The climate conditions that push the monarchs north earlier are not also triggering earlier sprouting of milkweeds. Nectar plants also are too young to offer many flowers.
What adaptations are needed for monarchs to manage life as usual in 2055? They either must fly further from their overwintering sites before stopping to lay eggs (based on breeding habitats being further north) or they must overwinter in new sites closer to the new breeding habitat (overwintering needs are also complex). Let’s look at where breeding habitat is now in April (Map1, left) compared to where it will be in March 2055 (Map 4, right). Although the maps don’t show the same month, in 2055 areas of suitable breeding habitat in March (pink areas) generally will be north of what now is suitable habitat in April except for a portion of the Atlantic coast and the Oklahoma region. Will the monarchs need to leave their overwintering sites earlier and will the environmental triggers for migration alter?
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Also, consider that in the end of summer, monarchs must fly south to their overwintering habitat through the U.S. to Mexico. The pink area in Map 6 (suitable habitat in 2055) is much further from Mexico than their current summer range. Will they be able to fly this distance? Will the longer migration in autumn use more of the stored lipids that keep them alive through the winter to complete their migration north the following spring?
How can conservation biologists help monarchs adapt to these changes? Obviously, we need to ensure that nectar and milkweed host plants are available in the new territories suitable for monarchs. Will the biochemicals in milkweed and the nutrition in nectar in 2055 be equal to present levels? Some winter breeding now occurs, primarily along the Gulf Coast of the U.S. Will monarchs breed more often in winter? If this happens, milkweeds and nectar plants will be needed in the overwintering areas, although perhaps this won’t include the high mountains of Mexico that host the most monarchs now.
The two maps below compare the current known distribution of milkweed (generally) on the left and on the right is where milkweed will grow under moderate climate change conditions. In more severe conditions the milkweed is even further north and mostly absent below the Great Lakes. Where will the first generation of monarchs be bred if the milkweed keeps moving north but the monarchs continue to migrate south? Look above at Map 4 (on the right) that shows the suitable breeding habitat in March 2055. The map on the right below shows there is no milkweed in the 2055 March breeding habitat.
Look further up at Maps 5 (June 2055) and 6 (August 2055). The milkweed range shown below on the right coincides with breeding habitat in June 2055 but not as well with August 2055 (presently the time when the migratory supergeneration hatches). Will we help monarchs by planting more milkweed further north, and in the south along the Gulf Coast and the southeast Atlantic Coast? Will doing this encourage monarchs now to breed out of season and harm their populations (e.g., higher levels of disease are common with winter breeding)?
Conservation biologists don’t have answers to these questions yet. And the information presented here oversimplifies the situation by limiting our examination to a few issues, omitting all the details of the migration period, overwintering habitats, predators, diseases, and summer range conditions. But biologists are thinking ahead. We are asking the hard questions and being realistic about what might result from varying amounts of greenhouse gases being added annually and the increased temperatures that can result.
It isn’t just monarchs whose adaptations are being tested. It’s the milkweeds, all the flowering plants that provide nectar, and entire ecosystems cradling these plants and butterflies. Our ability to think flexibly and realistically is being tested. Milkweed needs to move north before the monarchs begin to use that habitat or there will be no host plants for eggs and larvae (unless monarchs really adapt unexpectedly and use other plants, perhaps if their predators don’t move with them and they don’t need to feed on toxins to deter predation?).
A big shift is already happening. For monarchs to thrive in 2055, their entire habitat that now stretches from Mexico and across the U.S. to southern Canada must not only move geographically, but it must function as an ecosystem. Conservation has altered from let’s put these habitats back together and protect them to include where are these habitats going?
Do we have world enough? How far north can monarchs, milkweed, and their habitats move before running out of world? And time? The model projections used here are only 38 years from now. Will this occur sooner? Will something we don’t see right now attenuate the effects and give everyone more time?
This is why I am a conservation biologist and why I have spent my life helping mitigate the ecological consequences of human meddling. I want monarchs to fly into a future I won’t see.
1. Climate change data and mapping from these sources unless otherwise noted in the text.
- Nail, K.R., R.V. Batalden, and K.S. Oberhauser. 2015. What’s too hot and what’s too cold? Lethal and sub-lethal effects of extreme temperatures on developing monarchs. In Oberhauser, K.S., K.R. Nail, and S.M. Altizer, eds. Monarchs in a changing world: biology and conservation of an iconic butterfly, Chapter 8. Cornell University Press, Ithaca, NY.
- Zipkin, E., L. Ries, R. Reeves, J. Reetz, K.S. Oberhauser. 2012. Tracking climate impacts on the migratory monarch butterfly. Global Change Biology 18:3039–3049.
- York, H. & K.S. Oberhauser. 2002. Effects of duration and timing of heat stress on monarch butterfly (Lepidoptera: Danaidae) development. J. Kans. Entom. Soc. 75:290-298.
- Batalden, R.V., K. Oberhauser, A.T. Peterson. 2007. Ecological niches in sequential generations of eastern North American monarch butterflies (Lepidoptera : Danaidae): The ecology of migration and likely climate change implications. Environmental Entomology 36: 1365-1373.
- Nail, K.R., and K.S. Oberhauser. Monarchs in a Changing Climate: An Overview. In Oberhauser, K.S., K.R. Nail, and S.M. Altizer, eds. Monarchs in a changing world: biology and conservation of an iconic butterfly, Part 3. Cornell University Press, Ithaca, NY.
2. Observations from Mexico and the U.S. for 2017 are personal communications.
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