Bees + The Climate Crisis: Drought (Ep. 5)

Bees are tiny little creatures, easily susceptible to any change in their environment. Extreme heat and drought have a significant impact on the diversity, abundance, and makeup of bee communities. Studies show that drought can have a stronger impact on the system than habitat fragmentation. Bees rely exclusively on blooming flowers for food, so if there are not enough flower resources available due to hot and dry conditions, bees will have trouble finding food. Additionally, hot and dry conditions can subject bees to heat and moisture stress, making it difficult for them to survive. We talk to Dr. James Hung from the University of Oklahoma about the devastating effects hot and dry weather can have on bees.

This is the study Dr. Hung, and I discussed in which he focuses on bees and what happened to them before and after a severe drought. The Hung Pollinator Lab is working to understand the effects of climate change on plants and pollinators. 

Be sure to listen to Episode 3, where we talked about how too much rain can be just as devastating to bees. 

Did you know?

Dr. Hung mentioned the sweat bee (Halictidae) as a bee that seemed to do quite well during the drought period in California. This is the second-largest family of bees, and they are ground nesters. Why sweat bee? They are attracted to perspiration and may try to get a lick of sweat. Sweat bees are not aggressive, although buzzing around hot bodies may make them seem a bit annoying. Only females can sting, and typically they sting only if they are disturbed. 

Transcript

[00:00:00] The climate crisis touches nearly every aspect of our lives. Severe weather, wildfires, floods, and pollution can all have a huge impact on our daily life and the future of our planet. In a previous episode, we talked about the damaging effect excessive rainfall and flooding has on bees. Today we’re going to look at the other end of the weather spectrum.

Rising temperatures can lead to more intense heat waves, droughts, and other extreme weather events. We’re going to get a deeper insight into how drought can affect our native bees from Dr. James Hung from the University of Oklahoma. James is a pollination ecologist and assistant professor, Oklahoma Biological Survey and Oklahoma Natural Heritage Inventory.

He’s also the head of the Hung Pollinator Lab [00:01:00] at the University of Oklahoma. James, welcome. Can we first talk about the differences you found in bee richness and diversity in your study on drought and habitat fragmentation concerning native bees? Yeah, of course. So this study that you’re asking about was one of the chapters of my PhD dissertation.

So I spent my first two years basically documenting bee diversity in these nice, intact, large natural reserves and in these small fragments of the same kind of habitat, but embedded in a sea of urban landscapes just to see how habitat fragmentation on its own could be impacting bee communities. And then a drought hit.

And I wasn’t able to get data in part because I was concerned that in those droughts, if I were to collect bees, that could really impact the populations and especially some of these smaller fragments. And then the drought ended and precipitation returned to normal. The plants started blooming again. So we started collecting more data to continue our study on habitat [00:02:00] fragmentation.

And then we looked back and said, Hey, actually this dataset could be a very helpful one to study how this really dramatic drought really changed the floral landscape of our environment, has impacted the bee communities. So we did the analysis and we found that in the years after the drought, both years.

So we had two years before the drought, two years of a gap during the drought, and then two years of data right after the drought where conditions have returned to normal. And we found that there were fewer bee species collected at those same sites after the drought ended. And also I think, more importantly, we found that the bee community became much, much more heavily dominated by kind of this weedy little bee called halictid.

It’s a sub genus of, uh, sweat bee. We colloquially call this group metallic sweat bee. That’s a very cosmopolitan group found everywhere in the world. And I say weedy because they’re often found in kind of suboptimal habitat. You know, [00:03:00] when you have intensive agriculture, when you have an urban landscape. These are often the last bee species to drop out from these human impacts, and this group of bees went from something like 10 to 20% on average of each site’s total catch to something like an average of.

50% or more across all the sites. So one of the impacts of drought, not only to reduce bee species richness in the years after the drought, but also to drastically change the bee community to strongly favor these weedy little social generalist bee species that I guess for some reason is really good at surviving these drought conditions.

I also need to mention that it’s not the same species of these small metallic sweat bees before and after the drought. So even within the community of these little sweat bees, there were shifts in which species were common versus which species were rare. And there are a lot of other nuances with this interesting [00:04:00] data set.

And I wish we had at least taken a look to see what kinds of bees are active and persisting on you know, the very few floral resources that are blooming during the year of the drought instead of just not collecting data. And that’s definitely something that we want to do in the future. But kind of going back to the original question, we did find that drought had a pretty profound impact on the diversity as well as on the abundance and especially the makeup of the bee community in these habitats.

In fact, we found that in some measures, drought actually had a stronger impact than habitat fragmentation did on our system, which I thought was pretty interesting and pretty important to note because my original study focusing on habitat fragmentation did already find some pretty profound impacts.

You know, when you cut up habitats into these little pieces, even if you preserve the plant community to look pretty natural, you’re losing a lot of bee species. You’re changing the community makeup, what species are present where. But [00:05:00] in some ways, drought is having an even stronger impact than the fragmentation that you can very clearly see.

And again, this is not, you know, comparing the bee community before the drought to during the drought. It’s comparing the bee community in good years on either end of the drought and there are these huge differences. So I think there’s a lot that needs to be unpacked there and a lot more to study. That is so interesting, you know, that what you found, especially concerning the sweat bee and how subspecies of it or whatever, kind of almost thrived in these conditions.

And it could have been they thrived because there was no competition, or, you know, I mean there’s all sorts of little specific things to think about. Do hot or dry conditions affect bees in other ways? I’m thinking about how they can affect a region’s floral resources, which is something you kind of touched on that you found in this study that the landscape was quite different.

But how else are these dry conditions really hurtful to the pollinators? Well, the main way, as you mentioned, is [00:06:00] the impact on floral resources because as you know, bees rely exclusively on blooming flowers for their food, whether they are social species like honeybees and bumblebees, whether they’re solitary species, whether they are

diet generalists that forage from many different flower species or specialists that only limit their foraging to one plant family or one genus. And even the parasitic bees that don’t collect their own pollen and nectar, but invade the nest of other bees require that there are nests of other bees who are successful in collecting pollen and nectar for them to invade.

So every bee species out there is reliant exclusively on blooming flowers to obtain their food. So if the climate is too hot and too dry, and there are not sufficient, uh, flower resources available to them, then bees will have a hard time getting enough to eat. But beyond just the impacts on a region’s floral resources, as you mentioned, the hot and dry conditions themselves [00:07:00] can impact bees.

So bees are pretty small creatures. They do span a large range in body size from maybe about two millimeters to, you know, four or five centimeters long for the really large species. But even the largest species are very small from the grand scheme of things, right? So, these bees are at the mercy of their surrounding environment basically.

So hot and dry conditions can subject them to heat stress and to moisture stress. There are studies out there already finding that in certain times of the year when there are heat waves and especially in certain areas where there are no places to seek refuge from high heat then species of bees that live in those areas, can suffer.

Also there can be moisture stress, so bees can lose a lot of their moisture when they’re just out and about forging just by respiring basically. And if there are not sufficient sources of moisture for them to rehydrate themselves [00:08:00] largely in the form of nectar from flowers, then it could be very difficult for the bees to survive.

There’s also evidence in the larger time span scale that bees are changing their body sizes as, uh, a function of how the climate is changing. So, uh, some evidence that bees might be becoming smaller, for example, as the climate warmed from year to year. So that’s something that, uh, scientists are still figuring out.

We’re trying to find out what is the cause of these patterns and what could the effects be for those bees and also for the plants that they pollinate. So does it seem that they are becoming smaller so that they don’t need as many resources? That’s a good question. You know, there’s a general pattern where in hotter places organisms become smaller.

So if you compare a coyote in the northern tundra versus in [00:09:00] southern Mexico, you’ll find that the coyote in the northern tundra, on average is a little bit bigger, um, insect species that spend large latitudinal spans also seem to have some of that same effect. Now, is it because when it’s very hot, bees have a hard time finding enough pollen and nectar to feed to their offspring and therefore their offspring become a little bit smaller?

Or is it because smaller bees, like you said, have smaller needs for food and therefore, can survive better in these hotter environments. I think that’s something that we still need to figure out. This is still a pretty new field of research, at least from the perspective of bees. So there aren’t a lot of answers out there, and it’s an exciting field of research.

How do warmer autumns and winters affect bees? I know the autumn is when bees are starting to prepare to over winter, so they’re quite busy at that time of year. And then in the winter, even though their hibernating is a warm winter, going to affect them [00:10:00] negatively come spring. Yeah, this is a great question and I think it depends on the context of how the warmness is presenting itself.

And also it depends on the bee species we’re talking about. So are we talking about like a generally milder winter where it just never gets all that cold? Or are we talking about kind of regular cold winter, but we have a bunch of freak warm days or a very warm stretch out of nowhere in the middle of it.

Just from my personal experience here in Oklahoma, I’ve spent last two winters here, and in both years we’ve had some really weird freak warm days throughout the winter, and most vividly I can remember early December, where after the temperatures have cooled down significantly, there were a few really warm days, like 20 degrees Celsius days.

And on those days I saw both honeybees and native bees foraging on the few flowers that still remained on some of the urban lawns and in the [00:11:00] wild, natural habitats, there’s no flower blooming already. But on these irrigated and manicured lawns, there were still some weedy native and non-native plants that are blooming, and they’re bees, even specialist bees out there

collecting pollen and I found that to be an interesting and kind of unnatural condition. So some species of bees are able to take advantage of the delayed kind of deep freeze of fall and winter. To what extent that can help their populations. I’m not sure. And it’s something that we need to continue to study, but

on the other hand, again, here in Oklahoma, we’ve had these freak warm days in January and February where there’s literally nothing blooming in the natural landscape. And we started trapping bees just to see if you know some bees are missing the cue and waking up from their slumber basically on these freak, warm days.

And indeed we found several different species of bees that have started their activity and finding nothing to eat ended up in our traps. [00:12:00] So, where at least punctuated warm winter days can certainly mess with the activity of bees and you know, what choices they make with respect to continuing their activity from the fall or starting the new year’s worth of activity in the spring.

Also, warm winters can mess with the metabolic rate of solitary bees that need to remain in suspended animation. We call this diapause. Basically, they lower their metabolism and you know, they don’t move a lot, they don’t respire a lot, uh, they conserve energy in the form of their fat storage, and they’re basically waiting for the right conditions to come along in the spring.

And when the winter is over all just warmer than they are used to, than the species is adapted to. They can burn through their fat reserves more quickly and end up in trouble. Sometimes they end up emerging earlier again when there’s nothing [00:13:00] to eat, just because they’re so desperate. Sometimes they simply don’t make it to the time that they need to emerge.

So warm winters can be kind of harmful to at least some of the bees that have been studied. Can you talk a bit about how climate change is disrupting seasonal connections between bees and flowers? To put it simply, bees and flowers have a long co-evolutionary history and they benefit from being active at the same time as their interaction partner.

So bees and plants as partners, but they don’t always respond to the exact same climate cues such as ambient temperature or day length, chilling hours. So, we are likely to get instances where bees could be emerging without their preferred host plant, or even in the case of some of the earliest spring emerging bees with absolutely nothing to eat.

It’s also possible for plants to start blooming with no pollinators to service them. [00:14:00] Especially when we get cases where it’s not just, you know, a monotonic warming from one year to the next with one year being just a little bit warmer than the previous year. But when we get these huge fluctuations in climate conditions from one year to the next.

So how can we help bees during periods of hot weather and drought? Is there anything we can do? I think as individuals, one thing we can do is to grow native plants in our gardens and water them so that they can serve as little oasis of food resources when natural landscapes might have very little to offer, especially if we live in places where there is already very little vegetation in the natural landscape to start with.

But I think what we can do as individuals is probably somewhat limited, but what we can do collectively as a society, I think is more important. And if we can preserve large pieces of intact habitat that’s well connected [00:15:00] to other parcels of good habitat, that’s probably the most important thing because bees like any other organism, need different kinds of resources from their habitat at different times of the year and in different kinds of environmental conditions.

So in San Diego, for example, where I did my dissertation, there are mini oasis from drought in the form of runoff zones of large boulders, right? So when rain falls on those large boulders, they wash off into little depressions of soil and those areas will get several times the amount of rainfall compared to just flat ground with no rocks around them.

So in a super dry year where only a tiny amount of moisture falls from the sky, those little runoff zones become little oasis where those are the only places that plants grow. So when you have large continuous pieces of habitat that’s connected to one another, and especially to a diversity [00:16:00] of slightly different micro habitats within them

so large rocks that form runoff zones for water. Ephemeral creeks that run through in the spring, uh, large trees that grow shade and decrease the local temperatures when you have habitats where these different kinds of conditions are all connected to one another, and the bees in the landscape have access to all these different kinds of micro habitats without being cut off by habitat fragmentation in the form of urbanization or intensive farming, for example.

These are the kinds of landscapes where bee populations as well as any other organism can bounce back after years of very, very poor climate. And my guess is that when you have habitat fragments that might look pretty decent in good years, but be cut off from a lot of these important resources in very adverse years, there are chances where you could have local losses of certain bee species, and it [00:17:00] might take a long time for them to recolonize those fragmented habitats.

Anything else you’d like to share about how dry conditions and climate change is affecting bees and other pollinators, or has the potential to? Well, I think we need to be studying these impacts a lot more, so we have a reasonably good idea of how things like landscape change, you know, urbanization, agricultural intensification, habitat fragmentation, how these impacts that are very visible and studyable and predictable, how these impacts are influencing bee populations.

But it’s much harder to study the impacts of climate and we really don’t have a lot of data on this topic relative to other anthropogenic stressors like land use change. And it’s also hard to study these impacts because we don’t know which bee species can maintain diapause for multiple years so basically, um, staying like a [00:18:00] seed bank under the ground or in their little cavity nests in twigs when they know.

that the conditions are not conducive to survival if they were to come out of their natal nests. And also, bee assemblages are kind of notoriously variable from one year to another at any given location anyway, even if you have several good years in a row. So right now it’s important I think, for us to get enough

data to cut through all the noise to see how climate change might be impacting bees, how they might be impacting the pollination services that bees are providing, and also what kinds of factors are perhaps exacerbating these impacts or ameliorating these impacts, and what species are most at risk of climate change and in what parts of the world so that we can properly direct our conservation efforts.

Like when we talked about the effects of too much rain on bees, there is still so much to learn about how to support bees and other pollinators [00:19:00] when the temperatures get too high. My thanks to Dr. James Hung for sharing with us his research in the danger of both heat and moisture stress to bees during periods of hot weather.

And thank you for listening. Do let us know what you think of the show. Are you learning something new? Do you have a bee topic or question you think we should discuss? Please tell us. Send us a message on our website where you can also sign up for our newsletter and read the show notes and transcript from today’s episode.

Find it all at thebeesknees.website. Thanks again for listening, and don’t forget to follow the show and tell your friends. I’ll see you in two weeks when we’re going to take a look at global bee diversity. Until then, keep buzzing.