Butterflies and climate change

We can’t talk about plant life without mentioning the animals that live in and around them. And pollinators are often in the news, with worries around declining numbers, and the impact on biodiversity and crop production. Andrew Bladon works at Cambridge University, where he’s done field work - literally - looking at how butterflies respond to temperature change. And he spoke to Chris Smith...

Andrew - So like many species, butterflies are showing effects of climate change at the population level. So we've seen that species are moving North in Europe and North America. And similarly to the plants that Chantal was talking about, species that are adapted to mountains tend to be declining and they're becoming more and more restricted. And there are also changes in behaviour. So species start to emerge earlier in warmer years. But all of these sort of population level changes that we can detect are likely to be caused by individual butterflies' responses to temperature. But we actually know very little about how butterflies respond on an individual level. So what we were trying to find out was exactly that - what do butterflies do to respond to temperature at fine scale? And can we link that to what's happening at a large scale?

Chris - And of course, the butterflies that do inhabit different environments that have different ranges of temperatures are going to be affected differently, in the way that you've just been identifying. So are there therefore some winners and some losers here?

Andrew - Yeah. So the interesting thing is that at the population level, research by butterfly conservation and long term monitoring over the last 40 years has shown that despite the fact that our climate is probably improving for the majority of species, about two thirds to three quarters of our species are still declining. The suspicion is that that's because there's still a big effect of habitat fragmentation and habitat loss on species. But within that, there are a few, a small number of species that are doing quite well. And species that are expanding their ranges northwards quite rapidly. And those generally tend to be the species that are more ubiquitous. They're the ones that can do well in lots of different environments. And they can survive in lots of different environments.

Chris - So the winners just win more and the ones that are already a bit vulnerable, they're finding it even harder to cope. Do you actually know, when you look at those winners and losers, do you know what it is that sets them apart? Why some are just a bit more resilient and some are more vulnerable?

Andrew - That's something that we've been looking at specifically in terms of how they adapt their behaviour to different temperatures. But I'm going to hold off a little bit on telling you the results of that, because we've got a paper coming out in a couple of weeks. So if you watch this space, there should be more answers coming very, very soon. In general, as, as you'd expect really, species that are more able to cope with a broad range of temperatures, those that are able to adapt generally to a wider range of temperatures, tend to be doing better. And those which are very specialist and have very specific temperature requirements tend to be doing worse.

Chris - What about the services they provide to the plants? I started this by referring to the fact they are pollinators. People often overlook the role of the lepidoptera - butterflies, moths etc - in terms of their contribution to the pollination effort. What has been the impact of these changes on what will be the impact of these changes on our plants and flowers and crops getting pollinated?

Andrew - Yeah, so you're exactly right. So about 85% of crops within the EU are insect pollinated. And most people assume that that's all done by bees. But in fact, honey bees, which people think of as the most common pollinators, only actually pollinate about five to 15% of crops, which leaves the other 85 to 95% to be pollinated by bumblebees, solitary bees, moths and butterflies, hover flies, beetles, and all sorts of other insects. And so actually the diversity of the insect community is really, really important for crop pollination and is estimated to be worth hundreds of billions of pounds annually.

Chris - And so if we take your findings and we extrapolate them to what the impact might be on pollination of crops, does that mean it's automatically a worrying picture? Or is it just that because we don't think the overall numbers of pollinators are going to go down, just the diversity is going to drop, actually, we probably will get away with it?

Andrew - The loss of numbers is worrying, but as you say, because some are going up, there's potentially some buffering there, but the thing is that because insect numbers fluctuate quite wildly from year to year. And so some species will do well in one year and then badly another year. And at the same time, a different species will do badly in the first year and well in another year. And by having that diversity of insect pollinators in the landscape, it means that actually we can be more resilient. So in any given year, we've got more options for the species that can pollinate our crops. The worrying thing is that if we lose some of that diversity, we become less resilient. And so there are fewer options for species to pollinate and therefore the chances of us having a really bad year where pollination fails becomes more and more likely. And, actually, the reliance that we currently have and is developing worldwide on the honeybee for pollination is particularly worrying. Because essentially if something bad happens to honeybees, we've lost the diversity of wild insect pollinators that could be able to pick up the pieces.

Chris - What can gardeners do to help?

Andrew - One thing is plant a wide range of wildflowers, to help give insects a helping hand, things that flower throughout the season. Another thing is to try and reduce the use of pesticides and herbicides because they are directly killing our insects. And the final thing is to try and actually be messier in the garden. Mow less, and leave some taller vegetation, which helps insects to survive through the winter.

Chris - Andrew, thank you.

We also put this to University of Sheffield horticulturalist Ross Cameron...

Chris - So, Ross, basically mow less, chuck fewer chemicals on, have a messier garden. Would you go along with that?

Ross - Yeah. In principle, I would. I mean, I think we can go back to nature a little bit in the design of our gardens in that the slightly rougher approach provides a lot of benefits. It's a benefit for wildlife, but even for what I mentioned earlier about capturing rain, holding water, the ability to provide a better microclimate for wildlife, but also for ourselves, goes along with a slightly more relaxed attitude to gardens. And at the end of the day gardens are places we want to enjoy. And quite a lot of enjoyment comes from seeing nature. So gardens without butterflies, without birds are pretty poor soul, really.

Chris - Lawn. A well manicured lawn is often seen as the thing we all aspire to, but actually one person described these things as a sort of biodiversity desert, a horrible mono-culture that's very, very demanding on our time, of our input and returns very little value. A) is that true? And B) therefore, should I get rid of my lawn? And if so, what should I replace it with?

Ross - Yeah, the green desert! Look, manicured lawns have their place. If you happen to be in the luxury of having a croquet lawn or a grass tennis court, it has to be close mown and functional. The reality is most of us do a lot of management of our lawns, which are not necessarily to our benefit. You can let the lawn grow a bit longer. You can get the wildflowers coming in. You can have the pollinators and insects, and you can also retain that degree of respectability. We're using what we call "cues to care". So if you cut paths where through it, if you keep certain parts of it tidy, you can actually still have the best of both worlds, nice legible walkable paths through the garden. And at the same time, allowing some rough and ready spots within the lawn that actually attracts the wildlife and provides that resilience.