Importance of dung beetles

Hi. I’m Dr. Ali Birkett from Lancaster Environment Centre. My interest is in how environmental conditions are affecting different organisms. And for the last four years, I’ve been working on my PhD, looking at that with dung beetles in Britain. When I tell people I’ve been working with British dung beetles, I usually get two responses. One is, I didn’t know there were dung beetles in Britain. And the other one is, why? Well, to approach the first one first, there are dung beetles in Britain. And we have about 65 species. But they’re not the sort of dung beetle that you usually see on your wildlife documentary films.

Those are often filmed in places like Africa, where there are big mammals, and there are lots of large piles of dung. So there you get what are known as roller dung beetles. They take a small section of the dung, and they roll it away, and they bury it and feed their young with that. We don’t have any of that exciting type here. But we do have two types of dung beetle, which are tunnellers and dwellers. The tunnellers take the dung at just a small distance from where it’s dropped, and they bury it in the ground. The dwellers complete their whole life cycle within the dung itself. So those are our two types of dung beetle in Britain.

My work has been in the uplands, which is the hilly areas of Britain. And I’ve been looking at the dung beetles that’s out there and how they’re affected by the land use changes and the climate changes in those hills. Because dung beetles are really dependent on livestock, any changes within the livestock system and how the animals are managed will affect the dung beetles. The other implication of environmental change within the hilly areas is that as climate warms, the temperatures change at each different height. So what we’re seeing is that dung beetles, along with lots of other organisms, are moving uphill in response to that change.

So in answer to the question why I’m studying dung beetles, it’s because they’re really important in the systems that they’re found in. So they are a beetle, and they feed on dung. The adults feed on the liquid parts of the dung. And the larvae feed on the more fibrous material. So when a dropping is left by a cow or a sheep, the beetles fly in. They land on that dropping. The adults feed, they breed, and then they lay their eggs. In the case of the tunneller beetles, those eggs are usually laid within a small ball of dung that’s buried in the ground. And with the dwellers, it’s within the dung itself.

So the reason the dung beetles are really important is because of their activity within that dung. First of all, there are some dung beetles that are nocturnal and are actually really important food resources for greater horseshoe bats, which is a species of high conservation interest in this country. Other species of dung beetle are a key food resource for birds, because birds can turn over the dung deposit and pick out the beetles, the adults, and the larvae. In addition to that, within the dung itself, they are feeding on the dung, and they are breaking it down.

So one of the demonstrations I often give is if you think about a nice Sunday stroll through a sheep field, if there weren’t dung beetles and earthworms there, you’d be up to your knees in poop. That’s one of the reasons they’re really important. In places like Australia, where cattle were introduced, before the dung beetles were introduced that could feed on that cattle dung, you would get a pile of dung and then around that a set of vegetation. And the cattle wouldn’t graze on that, so you were gradually losing pasture over time. As more dung was dropped, more pasture was lost, because the grass underneath the dung itself wasn’t available to be fed on. And it wasn’t being broken down.

With dung being removed, it’s also important for the livestock. Because within a dung deposit, you get lots of parasites that are breeding and reproducing. So there are flies and things that are within that dung deposit. And if that dung deposit is left there, those flies will then go back and infect the sheep or the cattle in the field. If that dung is broken down, those flies obviously can’t survive. They can’t breed. And so the activity of the dung beetles reduces the parasite load that the sheep and cattle are being affected by. The tunneller beetles, particularly, have a really important role within the soil structure.

Because they’re digging tunnels into the soil, they are aerating the soil, and they’re breaking it up and reducing some of the compaction created by livestock. They’re also taking nutrients down into the soil. The dwellers are doing similar in the topsoil layer. Those nutrients are really important in the hill systems that I’ve worked in, because these systems usually are quite nutrient poor. So there is grass, but little trees, not much input of nutrients. So without dung beetles and earthworms that are putting the nutrients from the dung back into the soil, it would affect the vegetation that can grow. It would affect that soil system.

It would also affect the microbes within the soil, who wouldn’t be receiving the nutrients that they need to feed on. So one of the things that I’ve looked at is how dung beetle activity is affecting ecosystem respiration. Because the dung is being taken into the soil for the microbes to feed on, it’s increasing the microbial activity, which is increasing the respiration within the soil system. What do I mean by ecosystem respiration? I mean the respiration of all of the organisms within the ecosystem, so that’s the plants and all the micro and macroorganisms within the soil. So as there are nutrients put in, all of those organisms can be more active. And, therefore, they will respire more.

That will affect the gases that are released from the system, the greenhouse gases like carbon dioxide and others. And so you can see how the activity of dung beetles, on a relatively small scale, fits into the much bigger picture of how the system within the hills works. So as I was saying earlier, one of the things we were looking at within our hill system was how climate change and the temperature change that comes with that is affecting dung beetles. What’s happening as the temperature rises is that a particular site will be nice and comfortable for a particular species of dung beetle at present. But as the temperature warms, that site will get hotter.

It will be less comfortable for that beetle. So that beetle will then retreat uphill to find cooler places where it can still survive. That means, to test our original point, if some species are moving uphill, there will probably be a change in the community composition. Some of the lowland species will arrive at that site. And some of the upland, the top hill-dwelling species, will move out. So one of the things I wanted to look at was what effects that will have on all of those functions we were talking about earlier. Will the change in community composition potentially affect things like ecosystem respiration and the microbes within that soil system?

And what we found is that it is likely, with warmer temperatures and the change in community composition, there will be a difference within the way the ecosystem respires under those dung deposits. Within the discussion about changing community composition, one of the important things is whether the tunneller beetles that we were talking about are moving uphill from the lowlands. Because they are very different to the dwellers that are often at upland sites at the moment, they potentially have a really big effect on changing the function, because they’re digging into the soil. Again, as I said, they’re increasing the soil aeration, and changing the water flow within the soil, and all of those sorts of things.

So that was a key question for us, was whether the arrival of tunnelers would have a particularly big effect. We have seen in our data that there are indications that the arrival of tunnellers will affect ecosystem respiration. And it will increase the respiration at certain points within the life of the dung deposit. I also have colleagues in Brazil, and Borneo, and Australia that are also working on dung beetles and their different functions and roles within those tropical systems. One of the things they’re looking at out there is how dung beetles are affecting seed dispersal. So the seeds that are within the dung when it’s dropped, and that dung is then moved by the dung beetle.

It’s then transferring those plants, those seeds, across to different places. And what effect is that having on those tropical systems? It’s been really great to work with those people and to also see their libraries of newly discovered dung beetles. Because out in the tropics, there are thousands of species compared to our very small number. So it’s great to see them making discoveries in science in that way. So in summary, dung beetles are a key organism within the soil system, and they’re often overlooked, even though they’re also very sensitive to the changes in climate and land use that we are making to the systems that they’re found in.

I would say that, as I got off the internet, without dung beetles, we’d be in deep doo-doo.