Urban Buzz: Transforming Pollination in Cityscapes (Ep. 44)

Today, we’re taking a compelling look at the intersection of pollination and urban ecology, showcasing the resilience of nature amid the ongoing challenges of city life. Bees and other pollinators grapple with obstacles such as air pollution, artificial lighting, and limited green spaces. These factors disrupt the delicate signals bees rely on to locate and pollinate plants. Understanding how pollutants and changing pollinator communities affect these processes is pivotal. As our cities expand, ensuring sustainable pollination through innovative urban design and conservation practices remains a pressing priority.

Dr. Elsa Youngstead is an insect ecologist interested in how urbanization and climate change alter insect physiology, behavior, and mutualisms. Her Urban Ecology Lab works at the interface of urbanization and climate change, with a goal of understanding and managing ecological responses to modern stressors, such as changes in climate, air quality, and habitat structure.

Good to know

This is the study Elsa mentioned in the episode about pansies increasingly self-pollinting. You can read about urban pollination ecology in this article by Elsa and her colleague, Melina Keighron.

Transcript

[00:00:00] Welcome to the Bee’s Knees. I’m your host, Jacy Meyer. The Bee’s Knees is a podcast wild about native bees. Wild and native bees are under threat worldwide. In each episode, we look at actionable things we can do to support these adorable little guys whose pollination work is crucial for maintaining biodiversity.

Thanks for being here.

Pollination is vital for plant reproduction, but how does it fare amid the novel environmental conditions of our bustling cities? Dr. Elsa Youngstead joins me to talk us through the intricacies of urban plant reproduction and the fascinating dynamics of pollen movement. How do our bees handle the buildings, the streets, the sporadic green spaces of our cities?

To get us started, Elsa defines for us her field of speciality, urban pollination ecology. Sure, and I think, I mean, that’s kind of [00:01:00] three definitions, really, so we can do them all. I mean, urban has a fairly intuitive definition that Turns out to be hard to pin down when you really try to put numbers on it, but basically we think of it as, you know, an area that’s densely populated with people where we’ve built a lot of infrastructure, sort of buildings, roads, um, ways to, you know, to have transportation and energy.

And where the economy is mostly non agricultural. Of course, we have some agricultural activity in urban areas and pollination is super important for that. But mostly the economy also builds on sort of technology and service and other things. So, cities are these kinds of areas that are very dominated by, sort of, built structures.

And then in that context, you can have pollination ecology playing out. Pollination, of course, is the process, sort of a mating, reproductive process for seed plants where pollen is transferred from the male parts of flowers where it’s produced to the female parts of [00:02:00] flowers where it can, you know, germinate and ultimately fertilize.

an ovule, and then as a result of that, seeds are produced. But pollination is specifically the step in plant reproduction where pollen moves from flower part A to flower part B, and often it needs wind to move, or it needs an insect or another animal to visit the flower and transfer the pollen. And ecology then, of course, in general, is the study of, like, interactions between organisms and their environment.

And so pollination ecology is the study of sort of how plants and their pollinators interact and how that depends on the environment that they’re in, and in our case, the urban environment. So, one of the things you are interested in is the impact of urban settings on the plant pollinator signaling you mentioned.

Could you briefly explain this and share how this is altered in cities compared to more natural environments? [00:03:00] Sure, yeah. In terms of plant pollinator signaling specifically, you know, we’re talking about the ways in which pollinating animals detect and find the plants that they’re going to pollinate, which they don’t tend to go to them specifically for the purpose of pollinating.

They’re going there selfishly to get pollen and nectar to eat. Um, and then in the process, they end up transferring pollen as well, which then benefits the plant. And plants can attract their animal pollinators in a variety of ways. Visual cues, sort of size, shape and color are important. Scent is important.

And then the actual quality of the rewards that the plant produces. The nectar and pollen are also important for, if not attracting, at least sort of retaining your pollinators. And then on the pollinator end, you also have to be able to detect those signals and remember them, especially for, I mean, insect pollinators and vertebrates are both capable of learning and navigation.

And there are some species who will [00:04:00] have kind of a set, you know, route of flowers or plants that they visit on any given day that they repeat and come back to. And so. Anything in the environment that changes like the signals on the plant end or the receiving or memory on the animal end can alter that interaction.

And as far as what’s actually happening on the ground in urban areas, it’s not incredibly clear yet. But we know from experimental results, there are some concerns. There are some things that might be happening that need to be followed up on like with on the ground studies. So things like. Air pollutants, ozone, and diesel exhaust can just chemically destroy the scent plumes produced by plants, um, such that bees and other pollinators would be unable to detect them or only detect them in a much closer range than they used to.

And then those same, some of those same pollutants can also interfere with learning and memory in insects. So not only [00:05:00] are they reduced, not only is the signal that can detect reduced, but their ability to detect it and then remember it could also be reduced. And this is all sort of based on laboratory experiments.

We don’t know quite how important this is in the field compared to any of the other stressors that urban plants and pollinators might experience. So air pollution is a potential biggie. Artificial light at night can alter, you know, what plants are, you know, that night blooming plants, sort of what they’re doing, what kinds of signals they’re producing, and the ability of bats or moths to detect and respond to those signals.

And then, of course, also, as far as the, the rewards that a plant is producing that would attract and retain its pollinators, if it is, You know, growing in a sidewalk crack and sort of drought stressed and in the beating sun, those kinds of urban conditions can also affect its ability to produce rewards that would, you know, actually attract pollinators.

So all of those things are potentially happening. They’re [00:06:00] part of a milieu of other stresses in urban environments. That definitely need more study to understand kind of how much, how big of a deal they are in the overall scene of urban pollination. Can you share some thoughts about sustainable design and how that can potentially positively influence urban conservation and ecosystem services?

I think I’m maybe not at a place yet to share, like, very concrete recommendations. Like, we need to do exactly this design scheme to ensure that pollen is moving among plants and they’re reproducing sustainably, and as a result of that sustainable reproduction, they’re providing a healthy green space for us, visual cues that reduce our stress and our blood pressure.

Like, there’s all of these things that we know that urban green spaces, that urban plants do for us. That are great. Everything from, you know, reducing our stress to improving the quality of our stormwater and that for those [00:07:00] plants that provide those services to survive and thrive and sort of have sustainable populations in urban areas that we don’t have to, you know, hand pollinate or replant every generation.

They need their pollination ecology to be working around them in the city. And, you know, despite some of the potential challenges that I mentioned for a lot of plants, it does seem to be working. Like they are reproducing in urban areas. Some become rare in urban areas, perhaps due to pollination issues.

And so the question is then what can we do in our urban areas to make sure that, you know, any new plants that we install, any sort of green infrastructure will be sustainable, will be able to kind of maintain its own. Reproduction, and there is evidence in some urban areas of plants, particularly like rarer species or native species that have like population genetic signatures of not great reproduction.

You know, knowing we know that. Like, small populations in isolated [00:08:00] green spaces have, in fact, become reproductively isolated from each other, too. They’re maybe losing genetic diversity. Their pollen isn’t crossing the sort of urban gap between the small populations, which can reduce their chances of success.

So, Exactly how do we design a city that, you know, creates those sort of pollen pathways between small isolated populations. I think that’s still an open question. That’s something that, like, in the long term, my lab is interested in. We have some ongoing work to try and track. Bee movements, hence the movement of the pollen that they carry across urban areas, and try to understand sort of which parts of an urban landscape are barriers to their movement versus might facilitate their movement.

Buildings turn out to be a big barrier. It’s not like we’re going to have cities without buildings, but maybe by understanding what it is about the buildings that is, A deterrent to bee movement [00:09:00] would give us ideas for, you know, how to either help guide them around those buildings or over them or to make buildings themselves, you know, more navigable by urban pollinators.

So those are some of the things that we’re thinking about. Okay, so how do you study pollen movement? In my lab, we’re trying a couple of different approaches. One thing we’ve done, and this is a very classic method that people have been using for decades, but you can take a fluorescent powder whose little particles are about the size of pollen grains and put that on a plant as a marker and then see which other plants it shows up on.

So. There was a study that was led by a student in my lab, Oliver Ripper, I think summer before last was when he did the fieldwork. But we had cucumber plants set up on either side of buildings, on either side of roads, on either side of lawns, forests, gardens. And then we would put different colored dyes on the flowers and see sort of which landscape features that [00:10:00] dye moved across and which ones it did not.

So that’s one way of doing it. Population genetic approaches can also give you, like, population genetics of the plants can sort of tell you who’s mating with whom, or population genetics or paternity analysis of plants can tell you sort of who’s mating with whom and therefore where the pollen has been going.

And then one, that’s not something that my group does, but it’s a really cool way of looking at sort of how plants are connecting with each other by mating. And then another thing that we’re working on in my lab is actually like telemetry tracking of bees themselves. So that doesn’t necessarily tell you exactly which plants are pollinating which other plants, but it does tell you, you know, how the pollinators are moving through the urban environment, how far are they foraging, what plants are they visiting, and potentially connecting versus, you know, which plants might be left out of their foraging routes given their, Urban choices.

You’ve identified a number of knowledge [00:11:00] gaps in this area. Where would you like to see the research go? In my group right now, we are especially kind of excited about this connectivity and movement question. We also have a project ongoing with a little butterfly. Like, we study both bees and butterflies.

And ants, but not them, not so much from a pollination perspective. For bees and butterflies we’re interested in how they’re moving through urban areas and connecting the different resources that they need through this, like complex habitat. That’s a mixture of like buildings and roads and plants. It’s very patchwork.

And so that’s something that’s exciting to us. And I think Really relevant to being able to support not just plant reproduction, but also, you know, the populations of pollinators that will be able to then provide that service on down the road. But more broadly, I mean, things that I think we need to know about urban pollination ecology, whether my lab is going to do it or not.

I think some of those signaling questions are really interesting and important, like understanding how pollutants [00:12:00] are affecting this process and how pollinator community change is affecting the process. Like, we certainly know that, you know, cities are very distinct environments from their outlying natural areas.

They tend to sort of filter out certain. Pollinators, others, maybe thrive and understanding how that, you know, the change in species composition of pollinators affects which plants are able to thrive or be pollinated in urban areas is also like an ongoing. line of research that I think will be helpful.

And hopefully we can kind of put all of these things together and have a better sense of the prioritization, like which thing actually needs the most urgent action to ensure that, you know, pollination will be sustainable as cities grow and, you know, continue to both spread and densify. I think urban evolution is another really fascinating and fast growing field of study that also links into urban pollination [00:13:00] ecology.

And we’re just kind of starting to understand because pollination, because it’s like mediates plant reproduction. It’s like very tied up in the evolutionary process by determining who actually reproduces plants with which traits actually like send seeds into the next generation. It’s very tightly linked and we’re starting to see interesting and Very suggestive results of plants in urban regions, potentially evolving toward like reduced dependence on pollinators for their pollination and investing less effort in attracting pollinators like there are examples is a really strong recent example from a paper that was published this year, um, of violets field pansies in the Paris region that, um, Compared to that same species in the same region in the 1990s, the plants living there now are self pollinating more often, they’re making smaller flowers [00:14:00] and less nectar, and that sort of corresponds to a reduced abundance of pollinators, which could kind of turn into a little bit of a vicious

circle, like the pollinators that are left are then also finding less nectar in the flowers that are there. So I think there’s a hopeful and a concerning story that we’re seeing these kind of changes. I mean, like plants are finding a way, but also like, it’s a pretty clear indicator of how much things have changed and how much human induced stresses on the environment are changing the pollination environment and are sort of stressing plant pollinator interactions.

So why do you do what you do? Why bees? Oh, why bees? There’s so many answers, like, they I mean, they’re cute, they’re always fun to study just because they’re like, they’re just such interesting little animals and how they look and how they behave. And they are, I mean, there’s also like the serious justification, like among pollinators, [00:15:00] like something like 90 percent of plants need some kind of animal pollinator to fully realize their reproductive potential.

And among animal pollinators, like bees are the heavy hitters because they’re using. Nectar and pollen throughout their entire life cycle. It’s not like they’re just visiting a plant for their own individual needs, but they’re stocking up on pollen and nectar to take back to their nest. So they’re just handling a lot more flowers and moving a lot more pollen than pretty much any other kind of insect or animal pollinator.

I studied ants in grad school, and then sort of went away from science for a while, and then, like the rest of the world, started learning about pollinator decline and concerns with bee health and how much we didn’t know about wild bees and their health. So the combination of that, plus them being charismatic, plus them being super economically and ecologically important, what else would you study?

So many things to unpack here. There are many mysteries of [00:16:00] urban pollination that still need to be unraveled, so we can put the answers to work in our urban landscapes. Complex challenges remain, like predicting pollen dispersal and looking at how the drawbacks of city living, like air pollution, also affect bees.

Promising work is happening, and we’ll be sure to keep our eye on the work Elsa and others are doing. Don’t forget to visit the website, thebeesknees. website, for more information about Elsa’s Urban Ecology Lab, and a link to the Pansy study in Paris that she mentioned in the episode.