From Bees to Biodiversity: Shaping the Future of Ecosystem Services (Ep. 35)

Understanding the importance of rare and declining bee species has become increasingly vital as biodiversity continues to face global threats. Today we’re looking at a study that delved into the role these bees play in pollinating three types of wildflowers and three types of crops across 72 different sites over several years. Our guest, Dr. Mark Genung, found that although these bees accounted for only about 15% of the total pollination, the true value of their contributions became clear when considering the “insurance value” of biodiversity. Using this thought process revealed that a diverse set of rare and declining bee species is crucial for maintaining ecosystem stability, even if they don’t appear to be major pollinators at first glance.

Dr. Mark Genung is a Professor at the University of Louisiana in the US and the Principal Investigator at the Louisiana Native Bee Lab. His research interests include how plants and their pollinators interact, from individual organisms to entire ecosystems, and analyzing the relationships between biodiversity and ecosystem functions in community ecology. This is his study we discussed in this episode.

Good to know

Plants were an important aspect of Mark’s study. When the team combined data for all plants, rare and declining bees contributed similarly to both pollination and abundance. But when looking at individual plants, their contributions could vary widely. For example, they found that some non-native plants got less pollination from these bees than expected, while native wildflowers got more. They believe that rare and declining bee species can be very important in specific situations, even if they aren’t widespread. They emphasize the importance of understanding when and where these species play key roles in maintaining the ecosystem functions that benefit us all.

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.

Biodiversity is critical for how well ecosystems work, but what happens when we lose some of that biodiversity, especially in big natural environments. In these places, it’s the rare and declining species that are often the first to go, but we still need to keep everything running smoothly over time and across different areas.

That’s what we’re going to talk about today with Dr. Mark Genung from the University of Louisiana. His recent study looked at the importance of rare and declining bee species in pollinating three types of wildflowers and three types of crops. [00:01:00] We’re also going to learn about ecosystem function theory, which is what I asked Mark to define for us first.

So the idea here is that we’re interested in how biodiversity of ecosystems effect functions that humans rely on, like pollination or flood protection, or, you know, carbon storage, anything like that. And this actually grew out of some very basic questions in ecology. So the first thing that we had noticed, this is going back 50 or 60 years, is that there is a relationship between how many species you have in a community, and the amount of productivity, new biomass that it produces each year.

So at first they were thinking about this with, um, the ecosystem function productivity. You know, you can think of that as carbon storage to make it more relatable, but as the predictor in that the amount of biodiversity was the response. Now over time, this kind of switched and people became more interested in how the amount of biodiversity was determining productivity rather than the other way around.

And this grew out of like some work by Dave Tillman in Minnesota [00:02:00] It was observational at first, meaning it wasn’t set up as an experiment. Uh, he was working on a nitrogen fertilization experiment and noticed that after a drought, some of his plots that just happened to have more species. These are like temperate grasslands in Minnesota.

So that’s the, what we’re talking about. Those that just happened to have more species by chance were a lot more resistant to the effects of this drought and it bounced back faster. So that was a very big study, but there were some critiques like, okay, yes, The number of species does change between these different plots, but other things that change as well.

So some words that we use to describe communities are like, Evenness. It’s one thing to say you have 10 species there. Evenness asks whether they’re present in similar abundances or whether one species is really dominant. So species change or the communities differed in things like evenness. It also differed in the exact identity of which species were present.

As I mentioned, there is also some nitrogen fertilization element. So people were concerned that like, why this is intriguing, it was not a [00:03:00] experiment designed to test that question. So then. You know, it really began a worldwide effort. I should say it’s probably more of a like Northern hemisphere, temperate regions thing, to be honest, but it was across many countries of experiments set up for that exact purpose saying, okay, we are going to control evenesss,

we’re going to control the identity of species as much as we can and set up experiments to see. How much the number of species really matters for ecosystem function. So the experiments were set up to answer this exact question. There’s some in Germany, some in the United States, across Europe as well.

And they all found very similar results. It was actually pretty exciting. Uh, ecology can be messy. So they found that, yeah, as you have more species present, you get an increase in productivity. The field was still really focused on productivity at this point. That increase tends to be very fast at first when you’re going from say one to five species, then it slows down eventually and tapers off.

So that’s kind of the background. And then more recently, and that’s all great. [00:04:00] Like these experiments were really well done. It was perfectly natural direction to take things. But more recently, there’s been this question of bringing this back to the real world, right? The reason we care about this question, like, And everyone who writes paper says this is, we want to know how ongoing shifts in biodiversity, so losses of species or species invasions, just declines in the abundance of a species, even if it doesn’t go extinct, how those changes are affecting things that really matter for humans.

That’s the pollination, the flood protection, the carbon storage. So there’s been an effort to say, we’ve learned a lot from these experiments. Let’s move back into closer to like a real world setting where these biodiversity function relationships are really affecting humans. And that’s a perfect place for you to tell us about your study.

If you could give us just a brief introduction, first kind of your thought process behind it and then the design of the actual research. Sure. Yeah. So before the study as a PhD student, you know, I was very much in that experimental world. Like I was setting up [00:05:00] biodiversity experiments. So I liked that. I think they’re useful, as I said, but the study came out of my postdoc work at Rutgers and Rachel Winfree’s lab.

And, you know, that lab was aligning with my own interest to kind of move into these real world systems, as I mentioned earlier. She had some data sets already together. So the crop data sets in the study, her lab had already put together. And we kind of supplemented those with the wildflower. part of the study.

So that was done by me while I was in her lab. She and I led that part of the research. And the idea was, you know, it’s kind of what I’ve said already to look at, you know, we’re not manipulating these bee communities in any way. We do set out plants just to attract them, but otherwise it’s the bee communities that are actually there in nature across a range of habitat types.

You know, we’re looking at, and we look at, you know, how many species are present, what the evenness is, how many pollen grains they deposit per visit. And this allows us to get at. You know, back in these natural systems, what is happening in terms of [00:06:00] the relationship between not only species richness, but any of these abundance, evenness, things that we use to describe communities, how are they affecting the amount of pollination that different plants receive?

There are many things that stood out for me in this study, but one of them was the large variability in the contribution of rare and declining bee species to pollination in different places and times. What do you believe are the primary factors driving this variability? Yeah, so there’s a lot of variability.

And again, as you mentioned, we did focus on the rare and declining species in this study. And so for rare species in particular, Well, a species can be rare in many ways, but not to get too much into the ecology weeds. What, in general, a property of rare species is that they tend to be concentrated in a few places, right?

So a species can be rare, and you might still find 100 individuals of it at a certain place, but you go to 50 other sites and you don’t find it at all. So that’s one way a species can be rare. I think it’s built into the nature of [00:07:00] rare species having these very patchy distributions where they often, not always, but they often have these patchy distributions so that they’re present at high numbers in a few spots and then kind of absent from other places.

So that leads them to, you know, that explains it to some extent. But ecology is also just a really messy science. Like there’s huge variability and the identity and abundance of species over time and space that we can’t fully explain. So, so like You know, anytime I come into a community ecology study, especially one that’s using observations and not experiments, I expect this like huge range of variability and when what’s there and, you know, I think in general we’ll struggle a bit to explain why, but I do think that patchiness like one thing I can point to for sure is that that naturally patchy distribution of rare species.

I guess another thing, this isn’t exactly your question, but building off that, you know, there’s also variability across the plant species. Like some, a rare and declining bee that’s very important for blueberry, for example, might not be [00:08:00] important for the wildflowers. So that kind of hits on similar issues, I think.

With the blueberry and the cranberry, we have native crops that evolved in the Eastern United States and have bee communities that evolved with them. So they are more reliant on specialists. They also have kind of. their flower structure and the way that they release floral rewards to pollinators is different and requires a bit more specialized handling.

So I think we’d expect, and if I recall correctly, we did see that the rare and declining species, if they were specialists on these blueberry or cranberry native crops could be very, very important for that reason. The watermelon’s a bit different. It’s an African crop that’s introduced. So, and it doesn’t have that same, specialized pollen release mechanism, but, but I think that plays into it as well.

Like there’s an element of rare species, perhaps being a specialist on one of these plants, but, but absent from others. And then that can lead to them being considered important as well. Can we talk about the practical implications of the [00:09:00] research findings? Um, specifically I’m thinking for biodiversity conservation and pollinator protection efforts.

Once you take this different approach of saying we want to maintain function at many places and many times, you need a lot of species for that. What I think is the neat contribution of our study is, when you first make that statement, we need a lot of species to maintain function across time and space.

Someone might come back and say, okay, but the whole framing of this question is, what is going to happen with real world changes in biodiversity and how those affect functions. And we know that these real world changes in biodiversity are not random. They target certain species. Those that are declining or rare.

So what we could add to that here was, all right, that’s a good point. But even if we subset this down and just look at those species that are likely to be lost, we find a similar kind of recommendation here that, that, um, you know, when you look across space and time again, you really do need a lot of species to.

It seems to make these [00:10:00] ecosystem function values that you want to hit. So where would you like to see the research go in this area then? So I think one thing Like, if we’d had more people, more time, et cetera, we set some kind of arbitrary thresholds in the paper. When we were like, what pollination threshold do you need to meet to say this is enough?

What’s the minimum set of bee species that can meet enough? The thresholds we chose were kind of arbitrary, and that’s common in ecology. That happens a lot, and you usually handle it with a sensitivity analysis. You say, let’s explore a few lower, a few higher than what we picked and see if it really liked it.

qualitatively changes their results in some way, which we didn’t see. But I think that is definitely a direction for improvement to go into these plants and say, what’s the maximum number of seeds they can set? How many pollen grains do you need to meet that? Instead of just choosing them, I think the threshold we chose was something like 50 percent of maximum pollination across sites.

I don’t think that’s a fatal flaw, but I think a [00:11:00] potential improvement would be to really dig into the plant side of things and have a more informed threshold for like, What does the plant actually need to maintain some level of its seeds? And taking it even further, this would be, it becomes a lot of work quickly, but you might want to figure out, okay, but maybe the plant doesn’t need to reach a hundred percent seed set to preserve itself on the landscape.

Maybe it needs 75 or 80. So digging into that question as well. Again, both of these things would be a lot of work. I think that there are natural progressions of trying to make this a more applied, more like relevant to real world settings. Both of those suggestions could do that. So why do you do what you do?

Why bees? Well, I didn’t start with bees actually. The first thing that drew me to this is really just an interest in community ecology. So just to be clear about what that is, a community in the biology world is many different species living together at a certain place in time and [00:12:00] interacting. So community ecology is like focused on studying those species interactions, properties of the communities like richness, which is the number of species, evenness.

So I was really drawn to that. Like I just found that to be really interesting and, you know, it’s challenging because that data can be very messy. So it creates analytical challenges. And I enjoyed that part of it. I switched to these, to your question, um, during the postdoc and Rachel’s lab, as I mentioned, I mean, that, that was the focus of their lab.

They had wonderful people there for that. So it was a great opportunity to learn skills that really didn’t. I mean, there was no reason not to like, there are great resources there to build a new skill set. You know, when I started there, there had just been this new federal program put in place for pollinator protection.

Um, so there’s like increased funding and awareness. Pollination is a really important ecosystem function. And so yeah, so there’s a lot, I guess one last thing is it’s a very natural way to go. If I’m interested in going from experiments to more observational [00:13:00] work, which I was. Uh, pollinators are a natural fit for that.

You can do an experiment with plants. You can get clones of a certain plant species and plant them. Um, pollinators, the work basically has to be observational. Uh, a group of species that are very important to humans, that there’s a lot of public interest in, And a lab that had great resources for doing it well.

Yeah. So yeah, it was just a natural fit in many ways. There’s no reason not to do it. My biggest takeaway from the study was the real world importance of protecting biodiversity to keep our ecosystems functioning properly. Every living thing has a vital role to play and we depend on their survival for our own.

Thanks to Mark for a fascinating conversation. And thank you for being here. There are more details about the study we discussed here on the website, thebeesknees.website, so be sure to check that out and please follow and share The Bees Knees. Your support for this podcast and the bees means a lot. Until next time,

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