About a century ago, there were lots of reports of migrating insects along the East Coast of North America. Among those were numerous sightings of large, apparently migratory congregations of flies. And then, for reasons no one seems able to explain, there is nothing about North American fly migration in the scientific literature for almost 100 years.
WHAT HAVE WE BEEN DOING THAT’S MORE IMPORTANT THAN FOLLOWING UP ON REPORTS OF MIGRATORY FLIES??
It’s unconscionable, really. There are flies. Migrating long distances. And no one thought to go out and learn more about this?
Ok, that’s not fair. There’s been some great work in Europe on migratory flies (and other insects) – much of it in topographic locations like mountain passes where flying migrants of many kinds are funneled through narrow locations. They’ve documented numerous fly species, especially in the family Syrphidae (hover/drone flies), making seasonal flights in huge numbers. There’s still an awful lot to learn, but at least they’ve made a good start.
What’s especially frustrating is that some of those same migratory fly species are here in North America, too, along with many other close relatives. If they’re migratory in Europe, they’re almost surely migratory here, right? So why has no one checked?
Eristalis tenax, the common drone fly, appears to be a migratory species in both Europe and North America.
Well, after the long, inexplicable century of ignoring this fabulous field of research, there have finally been two recent North American studies (One in California and one in Illinois) on the topic. Both have confirmed that flies do still migrate on this continent, but we still know almost nothing about which species migrate, where they go, and why. Let’s fix this!
In the meantime, while we don’t know much about fly migration here in North America – and have huge knowledge gaps in Europe and elsewhere – we can at least marvel at it. First of all, as is the case with most migratory species on our continent, fly migration is probably a way to escape cold temperatures in the winter and then to spread out (and escape competition) when temperatures are moderate. Birds aren’t the only animals cool enough to do this, no matter what snooty ornithologists will tell you.
(I don’t mean to imply that all ornithologists are snooty. In fact, many are surprisingly decent and nice to talk to. If an ornithologist was snooty, though, they’d surely be braggy about bird migration, wouldn’t they?)
You might not think of flies as cold tolerant animals, but many can survive sub-freezing temperatures. Body size is one predictor of that (bigger flies can generally survive colder temperatures.)
It appears that within at least many fly species, part of a population migrates south for the winter and the other part doesn’t. This is common among other insect groups as well. It’s a good way to hedge bets. If the subpopulation that stays put is wiped out by a particularly nasty winter, the migratory party can return and keep the species going. Or, if the migrants all die during their perilous journey, the ones who stayed home will persist.
How does an individual fly know if it’s supposed to migrate or hunker down for the winter? GEE, WOULDN’T IT BE GREAT IF WE KNEW SOMETHING ABOUT THAT??
Generally speaking, the assumption is that fly migration is a multi-generational phenomenon. The flies that head south in the winter have babies that then start the northward migration the following spring. By summer, either those progeny or their offspring will return to where their parents/grandparents had been the previous year. Of course, we don’t really know that BECAUSE NO ONE IS PAYING ATTENTION.
Drone flies like this one resemble bees but have bigger eyes, short antennae, and only two wings instead of four. THEY ALSO MIGRATE.
I’d love to continue this incredible, compelling story and provide lots more details. Unfortunately, as you might have gathered by now, we scientists have largely wasted a century doing less important work than fly migration research. As a result, I’ll just stop here.
This drone fly is clearly staring at us in astonishment because we’ve not been curious enough to learn about its (surely) epic migratory activities.
Almost a decade ago, I wrote about two competing metaphors for prairie restoration. I suggested we view prairie restoration like the reconstruction of a city after a disaster rather than like the restoration of an historic building. We need to concentrate on the roles and functions of prairie ecosystems rather than how closely a restored patch of prairie resembled what it used to be in the past.
Today, I’m hoping to stimulate conversation about the difficult decisions we face as we try to conserve prairies in the face of rapid climate change. One conservation planning approach is to focus on conserving the stage, not the actors. It advocates prioritization of sites with geophysical diversity because those abiotic conditions influence habitat heterogeneity, which supports biodiversity. The hope is that we might be able to conserve “an abiotically diverse ‘stage’ upon which evolution will play out and support many actors (biodiversity).”
The varied topography and the habitat size and connectivity found in Flint Hills of Kansas makes it a ‘stage’ that can potentially sustain biodiversity – but only with thoughtful, persistent, and adaptive management.
I think the ‘conserve the stage’ approach has merit, but it’s just a first step, especially for prairie conservation. We don’t just want to save the stage; we want to make sure the show goes on. Thus, I present to you a long (and potentially ridiculous) metaphor for prairie conservation that builds upon the ‘conserve the stage’ approach.
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Every actor in a theatrical production plays a role that helps tell a story. Likewise, every species in a prairie plays a role that contributes to the overall functioning of the ecosystem. In a healthy and resilient prairie, all the key roles in are filled.
Fortunately, there is a lot of redundancy built into prairie communities. We have lots of species that provide pollination, seed dispersal, nutrient cycling, and all the other essential functions that keep prairies going. We have a big cast, or maybe a big actors’ union.
Today’s prairie ‘show’ already looks different than it did in the past. Prairie landscapes are fragmented, invasive species have joined the cast, and the climate is changing. Those and other factors mean that some actors who played key roles in the past are no longer part of the show, at least at some venues. Other actors remain in the cast but don’t play their roles as effectively as they used to. Despite those changes, there are still really good versions of the prairie show being presented on various stages, though the versions vary quite a bit from place to place.
To keep the show going, we, as producers and directors, have to be creative and adaptable. We face really difficult decisions, especially when it comes to actors who aren’t well suited for their roles anymore. Continuing to direct the show with those actors as the main focus can weaken the performance of others and drag the whole production down.
Making changes to the cast of a show comes with a lot of risk, however. We don’t have a lot of experience with that process and we’re likely to make mistakes. Fortunately, in most cases, there are existing cast members that have the potential to adapt their roles and take on new challenges. With some guidance, those actors will find new ways to collaborate with each other and put on a show that might not be exactly the same as we’re used to but will still have a plot we can follow and enjoy.
More frequent and severe flooding is occurring as a result of climate change. That increased flooding will likely affect which plant and animal species will persist in low-lying prairies like this one. Can we predict those changes and help guide them in ways that don’t lead to reduced biodiversity?
If more drastic actions are needed, we might recognize that some actors are on their way out and start training understudies who can gradually take over roles as needed. If necessary, we might decide to recruit actors that are playing diminished roles on other stages and bring them in to rejuvenate their careers in a more suitable situation. Similarly, we might help some of our own long-term stars find new opportunities elsewhere, rather than just watching them slowly fade away.
In some cases, the world around us might force major a rewriting of the show itself. We might find ourselves directing a shrubland or woodland production rather than a prairie show. That doesn’t mean the show will stop or become less important, but it will require a different approach, a significantly altered cast, and a lot of adaptation by all involved. However, if we stick with the mantra of ‘The Show Must Go On’, we’ll need to figure out how to adjust on the fly and sustain as much biodiversity and ecological function as we can.
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Ok, I have to break away from this tedious metaphor. The real point here is that we can’t afford to be so invested in current or past versions of our prairies that we don’t allow them to adapt to changing conditions. At the risk of sliding back into my metaphor, there are lots of old movies and plays that don’t hold up well today. Jokes that used to be funny 20 or 30 years ago aren’t funny today. Old references don’t land with new audiences. In most cases, the basic stories themselves are still solid – they just need to be adapted for today’s world. Prairies and their species also exist in a different world than they used to, and that world continues to change (very quickly) around them.
The resilience and function of prairies is highly dependent upon biodiversity, which depends upon habitat size and heterogeneity, along with other factors. Maintaining high biodiversity in prairies that exist in fragmented landscapes comes with huge challenges, which are compounded by a rapidly changing climate. Plant and animal communities aren’t the same as they were in the past and they’ll continue to change over the next few decades and beyond. In fragmented landscapes, unless we take an active role, those alterations will largely take place in isolation, with limited opportunities for species to travel between one prairie fragment and another. Even in landscapes with large contiguous grasslands, we’ll need to be very thoughtful about how we shepherd those prairie communities through the coming years.
These tent caterpillars probably aren’t causing serious impacts to this patch of wild plum, despite appearances. How will climate change, habitat fragmentation, and increased woody encroachment affect this insect species and its impacts on other species in the future? (This is just a random example – I’m not saying tent caterpillars are going to become a major problem!)
It’s really hard to look at the prairies we know best and imagine them with a different composition of species. We’re used to measuring stewardship success by our ability to sustain the status quo. Watching the population of a species diminish in size – or disappear entirely – feels like a major failure. Most of us have also looked skeptically at any new species that show up in a prairie, worrying about potential negative impacts of that species on the existing community.
I don’t have a lot of answers to the big questions we face. I’m certainly not ready to lay out a plan or advocate for a particular approach to managing these changing prairies. As I did in another recent post, I’m mainly trying to get some conversation going on this topic.
The best I can do right now is offer a few ideas for discussion. For example, I think we might be smart to reevaluate the way we look at our objectives for prairie management. Instead of trying to maintain the current composition of plants and animals, maybe we should focus more on biodiversity and less on which particular species are present or abundant within those communities. (That doesn’t mean we welcome invasive species, by the way. Any species – plant, animal, or otherwise – that acts to reduce biodiversity is still a problem.)
I also think we need more serious conversation about when to resist ‘state changes’ like the transition from grassland to shrubland and when to facilitate those transformations, while trying to preserve as much biodiversity and productivity as we can. Again, I have little to offer in terms of specifics, but it seems clear that we’re not going to be able to stave off those state changes forever in at least some places. Let’s start thinking about contingencies instead of just waiting for those sites to collapse.
There’s a lot of woody encroachment in this prairie. The number of trees in the surrounding landscape and a changing climate are both spurring that invasion. At what point does the fight against this kind of encroachment become fruitless? What do we do then?
Finally, it’s never been more important to find opportunities to enlarge and reconnect prairie fragments through prairie restoration. The chances are slim that a small, isolated prairie fragment is going to adapt well to a rapidly changing world. Growing the size of those fragments by restoring adjacent patches should be a top priority. Can we find new approaches for creating those restoration opportunities in strategic locations? As we do that restoration work, we should also continue to test and discuss seed sourcing strategies, including the regional admixture approach, to see if we can further bolster the adaptive capacity of those small sites.
We’ll be figuring this out as we go, and we’ll surely screw some things up, but we can’t afford to just continue reacting. At the very least, we need to be thinking ahead about the changes that are taking place and how those will affect prairies. In some cases, we should probably be ‘acting ahead’ to guide state transitions, migration of species, or simply changes in species composition within individual prairie sites.
What we can’t afford to do is live in the past. We’re hurtling into the future whether we like it or not. Let’s make sure we bring prairies along with us.
The Prairie Ecologist 