Category: climate change

Walking among bees with Steven Falk

Posted on by andy.winfield

By Nicola Temple

Steven speaking to us in front of the limestone
meadow. Photo: Nicola Temple
I thoroughly love watching insects visit my garden (aphids and a few other pests excepted). However, I have to admit that beyond broad groupings, bumblebee, honey bee, hover fly, fly etc, I’m not very good at identifying them down to species. This clearly isn’t necessary to enjoy them, but I do find that when I know a species, when I know its routines and habits (as much as anyone does), then I have a deeper appreciation for them. So, when the University of Bristol Botanic Garden offered a bee identification workshop with Steven Falk, I signed myself up.
Steven Falkhas had an interest in insects since his childhood in London in the 1960s and 70s. Insects inspired his artwork and his skill as an artist earned him the honour of illustrating the book British Hoverflies, which he began working on when he was only 15. He has gone on to illustrate and write many publications since, including my newly acquired Field Guide to the Bees of Great Britain and Ireland (Bloomsbury, 2015).
Steven began the talk with some fast facts about insects in England. There are about 24,000 species of insect in England, 6,000 of which are regular visitors to flowers. “The biggest slice of this insect pie is wasps,” he explained. Even parasitic wasps visit flowers, and all together there are around 2,800 species.  Bees make up a mere 280 species and hover flies another 280. However, though they are less diverse in terms of species, bees and hoverflies are both abundant and extremely effective pollinators – so they punch above their diversity, so to speak.
Steven holding a yellow-legged mining-bee.
Photo: Nicola Temple
We start our walk in the Botanic Garden in the limestone meadow, just beside the West Terrace and the pond. If you unfocus your eyes a little and stare across the flowers, it is alive with activity. Steven shows us Myathropa florea, a reasonably sized hoverfly that has distinct grey markings on its thorax. It has an aqueous larvae, which lives in little rot holes at the base of trees. Then Steven points out a bumblebee mimic, Cheilosia illustrata, which tends to spend time near Hogweed because its larvae tunnel through the stems and roots. Apparently you can tell the age of a forest by the species of hoverfly present because they are so closely associated with certain plants.
Within minutes we’ve also spotted a common carder-bee (Bombus pascuorum) with its chestnut thorax – though Steven explains that this can be quite variable. It has a longer tongue and so this species is able to get down into the clover flowers. But there are also some buff-tailed bumblebees (Bombus terrestris) flying about also, which have shorter tongues and so they bite a hole at the base of the flower to rob the nectar. We spot lots of honey bees (Apis mellifera), which Steven also explains can be extremely variable in appearance, ranging from the typical striped appearance to almost entirely black – the tell tale sign being that its hind legs hang down as it flies. We haven’t even moved on the tour and we’ve already spotted at least six pollinator species – probably far more, I just can’t write fast enough to keep up with Steven listing them off!
The ‘fuzz’ of lamb’s ear is used by the female
wool-carder bee to line her nest.
Photo: Nicola Temple
Using what he calls his ‘praying mantis’ technique, Steven grabs a yellow-legged mining-bee (Andrena flavipes), and holds it so that we can all have a look at it. The long antennae tell you that this is not a fly, however, Steven goes on to list the colour variations that you can encounter. With all of these colour variations, I’m pretty sure I don’t stand a chance of accurately identifying anything on my own!
As we wander past some Lamb’s ear (Stachys byzantina), Steven mentions that the female wool-carder bee (Anthidium manicatum), a solitary bee, uses the fuzz from the plant’s leaves to line its nest. Steven then spots a patchwork leaf-cutter bee (Megachile centuncularis) and explains that it doesn’t collect pollen on its hind legs, but rather on its underbelly. Using his insect net, he catches it and place it temporarily in a little tube so that we all get a chance to look at it.
We walk past the wall germander (Teucrium chamaedrys) and there doesn’t appear to be a single flower that isn’t being visited by a bumblebee. It becomes obvious that while many of the tour participants are interested in the bees, they are equally interested in noting down which of the plants in the Botanic Garden are popular with pollinators so that they can create more bee-friendly gardens at home.
A great pied hoverfly (Volucella
pellucens).
Photo: Nicola Temple
As one would expect, near the end of the tour Steven begins to discuss some of the challenges that our pollinators face these days. He discusses the use of pesticides and the loss of habitat. He mentions that more erratic weather patterns and mild winters can lead to mortality – the latter causing over-wintering bees to go mouldy. But, he also finds the silver lining, stating that some bee species are expanding their distribution due to climate change.
It was only the commitment to another tour that forced Steven to end our walk. His love and enthusiasm for insects was apparent and he could have no doubt gone on to discuss far more than he did.
I definitely had different expectations for the workshop. I’m not sure whether it was the term ‘workshop’ or my own background in biological sciences that set my expectations that we would be looking at example specimens and comparing their features so that we might be able to better identify them. This was more of a garden tour and pollinator walk, which was lovely, but I’m not entirely sure I feel better equipped to identify bees in my garden as a result of being on the tour. If anything, it has shown me how much variation there can be within species let along adding in mimics and related species into the mix!  In the end I bought the Field Guide because really, in the end, that’s what it takes…good ol’ practice! And if I’m unsure Steven said to send him a picture on Twitter and he’ll help me identify it, which is brilliant! Not to mention, he has a fantastic free site on Flickr with pictures and information about all the British species, which is an incredible resource.
Germander (Teucrium chamaedrys) attracts
a tremendous number of pollinators.
Photo: Nicola Temple
This is the Year of the Pollinator at the Botanic Garden, so there are any number of pollination themed activities happening this year, including a beekeeping taster day, short courses for encouraging pollinators to your garden, and of course the annual bee and pollination festival in September.  And if you happen to snap a great photo of a pollinator this summer, you can enter the Botanic Garden’s photography competition, which will earn you a signed copy of Steven’s Field Guide to the Bees of Great Britain and Ireland as well as tickets to the Bee and Pollination Festival, visit the website for more details on how to enter.

Bumblebees who brave the winter

Posted on by andy.winfield

By Nicola Temple

This past weekend, my family and I met with friends in the village of Shipham, in Somerset, for a walk. It was torrential rain, yet we were determined. We dressed ourselves and three children under the age of 10 in waterproofs and set out. We arrived at a local country pub, not more than 3 km away, resembling drowned rats. And as a Canadian living here in the UK, I still marvel at the fact that nobody took one bit of notice at the state of us. It’s what you do. You get wet. You find a pub. You hunker down for a hot Sunday lunch. And you hope it tapers off before you have to head out again. (It didn’t.)

Pollinators, at least of the flying insect variety, aren’t terribly keen on this kind of weather either. Most hunker down for the winter months as there is generally not a lot of nectar to forage this time of year anyway. How they do this depends on the species. Honeybees reduce the colony to a minimal size and rely on their honey stores to see them through, while they dance in order to regulate the temperature of the hive. Most bumblebee colonies die out completely and the queens that mated at the end of the season find a place to hibernate. Solitary bees may hibernate as adults or as larvae, emerging only when the weather conditions are suitable. To each their own.

Martin Cooper spotted this buff-tailed bumblebee queen
foraging on his Mahonia flowers in Ipswich on a sunny
January day in 2015.
Photo credit: Martin Cooper [via Flickr CC]

However, there is one flying pollinator that can be spotted this time of year here in Bristol, and indeed, other warmer regions of the UK. It is the common buff-tailed bumblebee (Bombus terrestris). This species was first spotted during the winter of 1990, in Exeter. Sightings have been increasing ever since and include nest-founding queens, workers and males, suggesting this is a winter generation of the species.

The mated queen will emerge from her subterranean dormant state (diapause) during warm winter weather and set about establishing a new colony. The potential cost of waking up early is that the warm weather could be short-lived and temperatures could plummet. The benefit, of course, is that there’s nobody to compete with for food. If successful, the queen can establish a colony before the other pollinators even wake up from their winter nap.

Introduced plants provide winter forage

Of course, there is potentially another cost to emerging early – there could be nothing to eat. Bees are able to forage at temperatures around 0oC, but if there aren’t enough plants in flower, they won’t find the pollen and nectar needed to sustain the colony. Few native UK species flower in winter, but species introduced by avid gardeners to bring some winter colour to the garden, also bring some much-needed food to the buff-tailed bumblebee.

Researchers at Queen Mary University of London and The London Natural History Society, conducted a study of buff-tailed bumblebees foraging in London parks and gardens during winter about ten years ago. They wanted to see just how much food the bees were finding as food is directly related to the success of the colony.

The researchers found that there was plenty of forage to sustain the colonies and, in fact, the foraging rates they recorded near the end of winter were equivalent to peak foraging rates found in the height of summer. This doesn’t mean that the winter-flowering plants, such as the evergreen shrubs of the Mahonia spp., are providing more pollen and nectar than all the plants in the height of summer. But it does mean that each flower might have more pollen and nectar available because there aren’t other pollinators out and about also using the resource. The bumblebees, therefore, don’t need to go as far to find an equivalent amount of food and so they can collect it at a faster rate.  

Strategies for tolerating cold

Buff-tailed bumblebees aren’t as tolerant to cold as some other bee species; workers will freeze solid at about -7.1oC while queens freeze at -7.4oC. The bumblebees can obviously find warmth in the colony, but they need to forage and therefore be able to tolerate short spells of cold during the winter months. They may even need to tolerate cold temperatures for up to 24 hours as bumblebees often overnight away from the colony when they are unable to return from foraging.

Researchers from the University of Birmingham looked at the different cold tolerances of this bumblebee species a few years ago. They found that 50% of workers died after being exposed to 0oC for 7.2 days while queens could last over 25 days at this temperature – likely due to their fat reserves. However, as the forage study showed, the bees seem capable of finding food sources closer to the colony during winter months, which may reduce the likelihood of them having to endure cold temperatures for a lethal period of time.

These bumblebees may also have adopted some strategies to help reduce their possibilities of freezing. Pollen is an ice-nucleating agent in that it promotes the development of ice at higher temperatures. Other insects have been observed to expel any ice-nucleating agents from their gut when they experience low temperatures to avoid freezing. While this wasn’t observed in the bumblebees, it is a strategy that individuals might employ when caught out in the cold.

The more frequent observation of buff-tailed bumblebees in winter is thought to be a result of warmer autumn temperatures brought about by climate change. In a study from 1969, researchers reported a 6-9 month dormancy of all bumblebees in southern UK, so in a relatively short period of time there has been a considerable change in their seasonal pattern. There seems to be some flexibility in these patterns among bumblebees and for now, establishing winter colonies seems to be working for the buff-tails. However, with so many of our pollinators under threat, there is obviously also concern among the scientific community that more frequent extreme weather events could also spell disaster for these colonies that have selected to brave the winter months. As gardeners, we can perhaps do our bit by planting some winter forage species.

This year, the University of Bristol Botanic Garden will embrace a pollinator theme, with the aim of highlighting some of the lesser-known pollinators that are so important here in the UK. We love our pollinators, but research is still revealing so much about their unique and complex relationships with plants. So watch this space as we share some of these wonderful stories through our blog. We will also be posting pictures of pollinators we see in the Botanic Garden on our Twitter feed and Facebook page. But to see these pollinators in action, take some time to visit the Botanic Garden. Make space in your busy schedule to watch nature at its best – it’s worth it.

Sources:

Alford DV (1969) A study of the hibernation of bumblebees (Hymenoptera: Bombidae) in Southern England. Journal of 
     Animal Ecology 38: 149-170.
Owen EL, Bale JS, Hayward SAL (2013) Can winter-active bumblebees survive the cold? Assessing the cold tolerance of 
     Bombus terrestris audax and the effects of pollen feeding. PLoS ONE 8(11): e80061.          
     doi:10.1371/journal.pone.0080061
Stelzer RJ, Chitka L, Carlton M, Ings TC (2010) Winter active bumblebees (Bombus terrestris) achieve high foraging 
     rates in urban Britain. PLoS ONE 5(3): e9559. doi: 10.1371/journal.pone.0009559 

‘Tis the season…or is it?

Posted on by andy.winfield

By Helen Roberts

As I sit at my desk this morning, staring out the window, the weather is dire. There is slanting torrential rain and high winds, a typical December day perhaps.
Here in the UK, the seasons are changing and we are experiencing extremes of weather. For example, we have had wetter, milder winters in the southwest over the last couple of years along with increased flooding, particularly on the Somerset Levels. And then there was the very slow start to spring this year, with temperatures well below average in April. This was followed by a very hot end to the summer and warmer-than-average temperatures throughout autumn.
These changes to the seasons are linked to global climate change and are throwing the UK’s wildlife into disorder and affecting the fine balance of habitats and ecosystems. This is not a good scenario for biodiversity in the UK. Seasonal timing is off. When seasons start and end is shifting, and the length of the season itself is changing, making ‘growing seasons’ a more fluid concept. There is also increased risk for most gardeners of a ‘false spring’. Many plants and animals are changing their geographical ranges in order to adapt to these changes.
One of the most significant effects has been the disruption of lifecycle events and these are manifesting themselves in different ways. Bird migration, insect emergence, incidence of pests and diseases and flowering times are being thrown out of kilter.  
Researchers from the University of East Anglia recently analysed 37 years worth of data from the UK Butterfly MonitoringScheme (UKBMS) and found that extreme weather events were causing population crashes of butterflies. Uncommonly high rainfall events during the cocoon life stage affected 25% of UK butterfly species. And more than half of species were affected by extreme-heat during the overwintering life stage, possibly due to the increased incidence of disease or the effect of a ‘false spring’, causing butterflies to emerge too early only to be decimated by a return to cooler temperatures.
Warm temperatures are not all bad for butterflies though, as they will benefit from hot temperatures over the summer months when they are in their adult form and resources are plentiful. However, if populations crash more frequently than they expand, these extreme weather events could threaten UK butterflies.
The spider orchid (Ophrys sphegodes).
Photo: Jacinta Iluch Valero via Flickr [Creative Commons]

Changes in seasonal timing are also knocking the relationships between plants and animals out of sync, including the delicate balance between plants and pollinators. Thiscan be detrimental to the balance of entire ecosystems. An elegant study carried out by scientists from Kew and the University of East Anglia found that earlier springs brought about by rising temperatures are affecting the relationship between a rare spider orchid (Ophrys sphegodes) and its sole pollinator, the solitary miner bee (Andrena nigroaenea).   

This particular orchid has a flower that resembles and smells like a female miner bee and it uses this deceit in order to lure the male miner bee in. The male attempts to mate with the flower and by doing so, pollinates the flower. The plant has evolved to flower at the same time as the male bees emerge, but before the females do.
What the researchers discovered, by looking at the data set going back to 1848, was that rising temperatures are causing the relationship between orchid and bee to break down. Although rising temperatures cause both the bee to emerge and the orchid to flower earlier, the effect on the bees is much more pronounced. The male bees emerge much earlier and the orchids now flower as the female bees emerge. This means the males are not “pseudocopulating” with the flower because the real thing is already available and so the rare spider orchid is having fewer pollinations.
However bleak this picture may seem, plants and animals do have the ability to adjust to seasonal changes caused by climate change, it is just whether they can adapt quickly enough for these intricate ecological relationships to remain intact.
Helen Roberts is a trained landscape architect with a background in plant sciences. She is a probationary member of the Garden Media Guild and a regular contributor to the University of Bristol Botanic Garden blog.


References

Plants more resilient than animals through mass extinctions

Posted on by andy.winfield

By Nicola Temple

The fossil record suggests that a diversity of land plants had evolved by about 472 million years ago (mya). There is evidence to suggest that plants made the move onto land as much as 700 mya [1], placing them in the midst of the five largest extinction events to have shaped life on our planet.

Researchers from the University of Gothenburg released a study earlier this year showing that plants have generally been more resilient to these extinction events than animals. They looked at more than 20,000 plant fossils to see how these mass extinction events affected plant diversity [2].

Ferns and horsetails dominated the
landscape by the end of the Devonian.
Credit: Nicola Temple

They found, not unexpectedly, that each group of plants fared differently through each extinction event – with some doing better than others. Though plants might experience mass extinctions, the researchers concluded that plants also began to diversify again quickly after such events, so that more new species were being generated than were being lost.

“In the plant kingdom, mass extinction events can be seen as opportunities for turnover leading to renewed biodiversity,” said leading author Daniele Silvestro.

The big five

Scientists have identified five mass extinction events since land plants have evolved.

Ordovician – Silurian mass extinction (approximately 443 mya): This event wiped out approximately 85% of sea-dwelling creatures, such as trilobites. It has been hypothesised that a huge ice sheet in the southern hemisphere led to the alteration of climate patterns, a drop in the sea-level and a change in ocean chemistry.

Late Devonian (approximately 359 mya): This event is likely a series of smaller extinction events that happened over several million years, but the end result was a loss of 75% of all species on Earth. Changes in sea level, multiple asteroid impacts and new plants that were changing the soil chemistry have all been attributed to this period of extinction.

Permian (approximately 248 mya): It is estimated that 96% of all species were wiped out during this mass extinction. Marine creatures were badly affected and it is the only extinction thought to have had an impact on insects. Hypotheses as to what led to the demise of so many creatures have included combinations of asteroid impacts, volcanic activity, methane releases and decreased oxygen levels.

Triassic – Jurassic (approximately 200 mya): A mere fifty million years after the Permian extinction, about fifty percent of life was wiped out again. Plants seem to have been largely unaffected by this extinction event, but many of the marine reptiles were lost as well as large amphibians and cephalopod molluscs. Large scale volcanic activity and asteroid impacts have both been credited for these extinctions.

This dinosaur can still be spotted in the Evolutionary Dell
at the Botanic Garden! Credit: Nicola Temple

Cretaceous – Paleogene (approximately 65 mya): This extinction event is well known for the loss of the dinosaurs, pterosaurs and ammonites. The prevailing theory for this extinction is the impact of a large asteroid off the coast of Yucatán, Mexico and the subsequent fall-out effects.

While each of these mass extinction events meant the widespread loss of species, they also opened up opportunities for diversification and new species. Had the dinosaurs not gone extinct, for example, mammals would likely not have diversified, compromising our own lineage as humans. Flowering plants experienced extensive diversification after the Cretaceous – Paleogene event and they remain a dominant group today.

The key to resistence might be in duplicate DNA

The Wollemi Pine (Wollemia nobilis)
on display at the Botanic Garden has fossils
dating back 200 million years.
Credit: Nicola Temple

The majority of plants have undergone one or more duplication events where an exact copy of their entire genome is created. This is known as polyploidy – multiple copies of the same genome. Bread wheat, as an example, is hexaploid as it has six sets of chromosomes. Research has shown that one of these doubling events coincides with the Cretaceous – Paleogene mass extinction, approximately 65 million years ago[3].

An extra set of chromosomes could be quite convenient during a prolonged period of stress, such as a massive asteroid strike and its subsequent effects.  Polyploids might be better equipped to resist harmful mutations or perhaps take on mutations that offer a selective advantage under new conditions. Polyploidy plants also tend to be self-fertilising or asexual reproducers, which would be another advantage at a time when finding a partner for breeding could be limited.

Looking forward to a time of inevitable change

The theory that polyploidy confers an advantage during times of change can be witnessed in today’s extreme environments. There is evidence from the Arctic that polyploid plants are more successful than diploid plants at colonising habitats left by receding glaciers [3].

The Evolution of Land Plants Display at the Botanic Garden
(wrapped up for winter) is a walk through time.
Credit: Nicola Temple

Looking into extreme and changing habitats, such as the Arctic, as well as back into the fossil record can give us some indications of which plant groups may be more resilient to the changing climate we are currently experiencing.

You can take a walk through time in the University of Bristol Botanic Garden’s Evolution of Land Plants Display. There you will see living representatives from the groups of land plants that lived from the Cambrian to the Cretaceous, including unusual plants like Wollemi Pine (Wollemia nobilis) with fossils dating back 200 million years.

References:

[1] ‘First land plants and fungi changed Earth’s climate, paving the way for explosive evolution of land animals, new gene study suggests’, Penn State Science < http://science.psu.edu/news-and-events/2001-news/Hedges8-2001.htm>
[2] Silvestro D, Cascales-Miñana B, Bacon CD, Antonelli A (2015). Revisiting the origin and diversification of vascular plants through a comprehensive Bayesian analysis of the fossil record. New Phytologist (in press).
[3] Yong E (23 Mar 2009) ‘Extra genomes helped plants to survive extinction event that killed dinosaurs’, Not Exactly Rocket Science [blog] <http://scienceblogs.com/notrocketscience/2009/03/23/extra-genomes-helped-plants-to-survive-extinction-event-that/>