For the past year I’ve been keeping a secret from all but a few trusted confidantes: the subject and title of my next book! My publisher – Pelagic – has now announced it on their website and so it’s time to make it public. “Birds & Flowers: An Intimate 50 Million Year Relationship” will be the first book that covers bird pollination in its entirety, going beyond just hummingbirds, sunbirds and honeyeaters, to consider the more than 60 other bird families that interact with flowers, and the tens of thousands of plants that rely on them as pollinators. You can read more about it on Pelagic’s website.
The 3D mock-up of the cover shown above features an illustration by my good friend Stephen Valentine, a very talented artist who you may remember produced this painting of waxwings that Karin bought for my birthday a few years ago. I’m extremely pleased with how Pelagic have incorporated this into the design of the cover.
The book will be available by autumn I hope, if my writing schedule goes to plan!
It’s been a couple of years since I last did a talk or workshop for the Wildlife Trust for Bedfordshire, Cambridgeshire & Northamptonshire. But I’m pleased to say that they’ve invited me back and you can join me tomorrow evening for an online introductory talk about pollinators and pollination in the UK.
The talk starts at 7pm UK time and full details of how to sign up are in the link below:
This is a guest post by Dr Annemarie Heiduk about a new species that she’s recently described.
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In an earlier blog post about the discovery of a novel Ceropegia species, Jeff’s finishing sentence was: “I wonder what else is still waiting to be discovered in the stunning grasslands of South Africa?”
I am happy to provide a first answer to this question: Ceropegia stylesii.
This new species does not have the tubular kettle-trap flowers typical of Ceropegia, which temporarily trap pollinators, but open-rotate corollas where the gynostegium (fused male and female reproductive organs) is freely accessible to pollinators. So, in the traditional sense, C. stylesii is not a Ceropegia. This needs some explanation here!
Ceropegia is a genus in the plant family Apocynaceae (Jeff’s favourite family of plants!) and therein the genus is placed in the subfamily Asclepiadoideae which originally was a family on its own (“Asclepiadaceae”).
Within this subfamily, the genus Ceropegia belongs to the Stapeliinae – a subtribe which comprises ca. 720 species. About 220 species thereof have exciting looking and very cleverly designed kettle-trap flowers which attract small flies as pollinators via deceptive strategies (see http://plantlifesouthafrica.blogspot.com/2019/07/plantlife-sa-volume-473-july-2019.html). The remaining species in Stapeliinae are the well-known stem-succulent stapeliads (ca. 355 species in >30 genera) and ca. 140 species known as Brachystelma.
With increasingly better molecular methods to study the evolutionary relationships of species in Stapeliinae, the traditional grouping of the species was illuminated as being artificial, i.e., species with kettle-trap flowers are not actually a natural group and Brachystelma species are scattered among them; the stapeliads are also nested in Ceropegia but as a single (monophyletic) group. These results based on DNA-sequence similarities are not compatible with the traditional generic concept in Stapeliinae, and as a result, changes were instigated.
Some colleagues wish to see all 720 species of Ceropegia, Brachystelma and the stapeliads merged into one single large genus Ceropegia, a solution which would entail more than 400 new name combinations. Others prefer to adopt a less dramatic change of concept and only include Brachystelma in an enlarged Ceropegia while keeping the stapeliads separate based on their monophyly and distinct vegetative features. This pragmatic solution considers both taxonomic and phylogenetic facts and reduces the previously multiple cases of paraphyly to a single case. More importantly, it avoids hundreds of name changes in the group. Both concepts are correct in their own right and justified, so it is a personal decision which one to follow.
The newly described species C. stylesii would traditionally have been placed in Brachystelma as it is lacking tubular kettle-trap flowers. After the inclusion of Brachystelma into Ceropegia, C. stylesii is placed within section Bowkerianae – a group comprising species both with and without tubular kettle-trap flowers. With the description of C. stylesii, the section now has 15 members of which 10 have open-rotate flowers. Among these, C. stylesii appears to be most closely related to C. gerrardii from which it can only readily be distinguished when in flower (see the lower most image above).
The flowers of C. stylesii superficially look like miniature versions of a dark-flowered form of C. gerrardii, which growths in the same habitat. C. stylesii flowers are only about 6 mm in size whereas those of C. gerrardii are about three times larger. While C. gerrardii occurs in grasslands throughout eastern South Africa, C. stylesii is believed to be endemic to Ngome, where it is known from two localities with a total of less than 10 plants. After the recent discovery of C. heidukiae at Ngome, the area revealed another outstanding member of this amazing plant group, and thereby once again proves its conservation importance.
C. stylesii is named for David Gordon Alexander Styles, botanical explorer and collector, to honour his valuable contribution to botanical knowledge in South Africa. David is renowned for “…his daring nature to go leaps and bounds for the specimen he is interested in” (see Chetty 2021), a statement I can readily confirm based on personal experience. Many of David’s collections (by now well over 6000 specimens donated to various herbaria) are novelties awaiting to be described. With C. stylesii, a total of five plant species bear his name. I am delighted that eventually a Ceropegia species could be named for him as David’s knowledge on the distribution and habitats of these special plants is of great value to my research on this plant group.
On Sunday Karin and I rode our bicycles down to the local beach at Nordstrand. It was a chilly day, maybe 4C, with a raw coastal wind that made it feel that much colder. Our local bit of shallow ocean – the Kattegat – is normally quite calm but there was a swell bringing in seaweed and the (very) occasional item of rubbish. I collected a golf ball but otherwise the beach was free of plastic. That’s the usual state of affairs here, despite it being a popular tourist destination in the summer. If only beaches elsewhere in the world were as clean.
As we walked Karin and I chatted about some of our plans for the coming year. We’re both working on our next books and relishing the process of swapping chapters to read out loud to the writer. The occasional hardy soul, also enjoying being out in the elements, passed us by and we nodded in acknowledgement. Above us the gulls were wheeling and calling, a constant reminder that they were here before us and will remain when we are gone. Moving from the strand line into the sand dunes we found a convenient bench to sit, drink from our water bottles, scoff some nuts and raisins, and admire the view until the cold wind won the argument and moved us on.
Walking back to the bikes we paused to look at the verdant moss growing on the steep faces of the dunes. Small seedlings had germinated in these planty blankets, a promise of growth and flowers during the year to come. Here and there birds had torn out sections in their constant search for insect larvae. Life goes on even in these cold days.
On our ride back through the neat summerhouses that are settled within the nearby pine woodland, male Great Tits were voicing their claims to territory. Spring is surely just round the corner, we hope.
Yesterday, Karin and I took a winter walk through one of the local woodlands, our feet crunching on the iced-over crust which is all that remains of last week’s snowfall. No doubt more snow is on its way as we approach the deepest part of winter here in Denmark. But seeing this holly tree reminded us that some parts of the woodland might remain snow-free no matter what the conditions.
Although I’m no meteorologist (and any who are reading this can correct me if I’m wrong), I suspect that two things are going on here. Firstly, the tree is sheltering the ground and reducing the amount of snow that falls below it. That umbrella effect is fairly obvious. But secondly, and more subtly, the small amount of warmth that there is in the soil is being prevented from radiating off into space by the presence of the holly leaves. So the warmer soil and surface layer of vegetation melts any snow that manages to make it through or under the holly’s canopy.
In both of these ways, the evergreen holly is affecting the microclimate of this part of the woodland. That in turn adds to the ecological heterogeneity of the habitat, proving greater access to food for animals, affecting the phenology of the ground flora, reducing local soil moisture, and so forth. All of these, in turn, will potentially lead to greater diversity of species with the local area.
On this blog and in my book Pollinators & Pollination: Nature and Society I’ve often written about evergreen trees, shrubs and climbers such as ivy, holly and mistletoe, including both their cultural associations (especially with Christmas) and their ecological importance. As so often is the case, the English poet John Clare thought about all of this two centuries ago. The quote I used in the title of this post is from his poem Winter Walk:
The holly bush, a sober lump of green, Shines through the leafless shrubs all brown and grey, And smiles at winter be it e’er so keen With all the leafy luxury of May. And O it is delicious, when the day In winter’s loaded garment keenly blows And turns her back on sudden falling snows, To go where gravel pathways creep between Arches of evergreen that scarce let through A single feather of the driving storm; And in the bitterest day that ever blew The walk will find some places still and warm Where dead leaves rustle sweet and give alarm To little birds that flirt and start away
John Clare (1793-1864)
This might be my last post of the year, and so it only remains for me to wish a Glædelig Jul and Merry Christmas to all of my readers!
All organisms – be they plants, animals, fungi, or whatever – interact with other species throughout their lives, in relationships that include predation, parasitism, commensalism, and the many and varied forms of mutualism. But when species are transported to a different part of the world, as has happened often during the Anthropocene, these interactions typically break down because usually only one of the participants moves. This loss of ecological relationships can play a role in whether or not a species becomes established in its new home, and has been mostly explored in the “Enemy Release Hypothesis” (ERH) which predicts that, by leaving behind predators or parasites or herbivores, a species becomes more ecologically successful and ultimately invasive in its novel range.
Less well studied, though potentially just as important, is the “Missed Mutualist Hypothesis” (MMH) which in a sense is the twin of the ERH. As well as leaving behind “enemies”, introduced species leave behind “friends” such as pollinators, seed dispersers, mycorrhizal fungi, defensive partners, and other mutually beneficial associates. Negative effects arising from the loss of these relationships could potentially balance the positive impacts arising from the ERH.
In a new quantitative review just published, we review what’s known about the MMH (currently much less than the ERH) and suggest some fruitful lines of enquiry. The study is led by Angela Moles, my collaborator at the University of New South Wales where I spent time as a Visiting Research Fellow in 2019/20 (see my blog posts about that visit starting here). The paper has had a long gestation and gone through several iterations and revisions since we started writing it in late 2019, not least caused by the covid pandemic, but I think that it’s all the better for it.
Here’s the full reference with a link to the paper:
Introduced species often benefit from escaping their enemies when they are transported to a new range, an idea commonly expressed as the enemy release hypothesis. However, species might shed mutualists as well as enemies when they colonize a new range. Loss of mutualists might reduce the success of introduced populations, or even cause failure to establish. We provide the first quantitative synthesis testing this natural but often overlooked parallel of the enemy release hypothesis, which is known as the missed mutualist hypothesis.
Meta-analysis showed that plants interact with 1.9 times more mutualist species, and have 2.3 times more interactions with mutualists per unit time in their native range than in their introduced range. Species may mitigate the negative effects of missed mutualists. For instance, selection arising from missed mutualists could cause introduced species to evolve either to facilitate interactions with a new suite of species or to exist without mutualisms. Just as enemy release can allow introduced populations to redirect energy from defence to growth, potentially evolving increased competitive ability, species that shift to strategies without mutualists may be able to reallocate energy from mutualism toward increased competitive ability or seed production. The missed mutualist hypothesis advances understanding of the selective forces and filters that act on plant species in the early stages of introduction and establishment and thus could inform the management of introduced species.
The question of whether interactions between different species are more specialised in tropical environments (as theory predicts) has intrigued me for a couple of decades. In fact it’s just occurred to me that August 2022 was the 20th anniversary of my paper in Oikos co-authored with Louise Cranmer entitled: Latitudinal trends in plant-pollinator interactions: are tropical plants more specialised? That paper was one of the first to seriously challenge an idea that was long-embedded in the scientific and (especially) popular literature, that tropical ecology was in a sense “special” and that the ways in which species parasitised, consumed, or engaged in mutualistic relationships in the tropics was different to what was happening in the subtropics and temperate zones.
Since then I’ve written about this subject in a number of publications, most recently in my book Pollinators & Pollination: Nature and Society and it’s inspired some other researchers to address the topic.
One of the real challenges with asking questions about how plant-pollinator relationships change over large geographical areas is obtaining good, robust data to analyse. It’s a challenge to convince science funding agencies to give money to spend many years travelling the world and collecting the kind of data that are needed. However we can gain some idea of the patterns, and potential processes, that drive the macroecology of plant-pollinator interactions by piecing together databases of interactions for particular taxa, gleaned from published and unpublished sources.
That’s what we have done for the family Cactaceae in a new study led by Pablo Gorostiague from the Universidad Nacional de Salta in Argentina. This collaboration started when Pablo visited Northampton back in 2018 and spent some time with my research group, including helping out with field work in Tenerife. Since then the usual issues (work, COVID, etc.) have delayed publication of our paper, but now it’s finally out. Amongst other results we find that, yes, tropical cacti are pollinated by fewer species on average (though it’s hugely variable – see the figure above) but that functional specialisation (i.e. the number of pollinator guilds that are used by species) is no different in the tropics compared to the extra-tropics (that’s the figure at the end of this post).
The full reference with a link to the paper is below; if anyone wants a PDF, please send me a message via the Contact page:
Biotic interactions are said to be more specialized in the tropics, and this was also proposed for the pollination systems of columnar cacti from North America. However, this has not yet been tested for a wider set of cactus species. Here, we use the available information about pollination in the Cactaceae to explore the geographic patterns of this mutualistic interaction, and test if there is a latitudinal gradient in its degree of specialization.
We performed a bibliographic search of all publications on the pollination of cacti species and summarized the information to build a database. We used generalized linear models to evaluate if the degree of specialization in cacti pollination systems is affected by latitude, using two different measures: the number of pollinator guilds (functional specialization) and the number of pollinator species (ecological specialization).
Our database contained information about the pollination of 148 species. The most frequent pollinator guilds were bees, birds, moths and bats. There was no apparent effect of latitude on the number of guilds that pollinate a cactus species. However, latitude had a small but significant effect on the number of pollinator species that service a given cactus species.
Bees are found as pollinators of most cactus species, along a wide latitudinal gradient. Bat and bird pollination is more common in the tropics than in the extra-tropics. The available information suggests that cacti pollination systems are slightly more ecologically specialized in the tropics, but it does not support any trend with regard to functional specialization.
It’s long been recognised that the scale at which we study the natural world – over long or short time periods, or across small areas or whole regions – affects the conclusions that we draw about ecological patterns and processes. This is certainly true of plant-pollinator interactions. For example, a widely distributed plant can have very different pollinators at the extremes of its range, and pollinators like bees may vary their focus on nectar and pollen sources from year to year.
The analysis of these interactions as networks of actors has become increasingly popular in the last couple of decades. However there is no consensus about how frequent sampling should be, or the geographical scale over which networks should be studied. In fact all scales (from regional “meta-networks” down to single-season, single-site, single taxon observations) are relevant, depending on the questions being asked or the hypotheses posed.
But it’s important that we acknowledge that conclusions drawn at one scale may not apply at other scales.
That’s the take home message from a paper published this week which is the latest output from the PhD work of Australian bee expert Kit Prendergast. We have collaborated on several papers based on her data and this is actually my 100th peer-reviewed publication: a proud milestone for me and one which I’m glad to share with a wonderful early career researcher like Kit!
Here’s the reference with a link to a read-only version of the paper:
Bipartite networks of flowering plants and their visitors (potential pollinators) are increasingly being used in studies of the structure and function of these ecological interactions. Whilst they hold much promise in understanding the ecology of plant– pollinator networks and how this may be altered by environmental perturbations, like land-use change and invasive species, there is no consensus about the scale at which such networks should be constructed and analysed. Ecologists, however, have emphasised that many processes are scale dependent. Here, we compare network- and species-level properties of ecological networks analysed at the level of a site, pooling across sites within a given habitat for each month of surveys, and pooling across all sites and months to create a single network per habitat type. We additionally considered how these three scales of resolution influenced conclusions regarding differences between networks according to two contrasting habitat types (urban bushland remnants and residential gardens) and the influence of honey bee abundance on network properties. We found that most network properties varied markedly depending on the scale of analysis, as did the significance, or lack thereof, of habitat type and honey bee abundance on network properties. We caution against pooling across sites and months as this can create unrealistic links, invalidating conclusions on network structure. In conclusion, consideration of scale of analysis is also important when conducting and interpreting plant–pollinator networks.
Within the last decade there’s been a growing awareness of the importance of urban environments for supporting populations of pollinators, especially bees. Indeed, I devoted a whole chapter of my book Pollinators & Pollination: Nature and Society to the topic, though even then I was only able to scratch the surface of the research that’s been done. Since then there’s been some important studies published and this 2020 review by Kath Baldock provides a good starting point for the topic, whilst a recent pre-print by Pietro Maruyama and colleagues emphasises how little we know about pollinators in tropical cities.
One of the most detailed studies of urban solitary bees in a British town was conducted by Muzafar Sirohi when he was a PhD researcher in my department in Northampton. The first paper from that work, documenting the diversity and abundance of bees, came out in 2015, but since then commitments to other projects, plus Muzafar’s return to his university in Pakistan, have meant that we’ve struggled to find the time to publish more. Hopefully that’s changing and the second publication from Muzafar’s thesis is now out, with a third in progress.
This new paper uses a network approach to study the use of flowers by these bees; here’s the reference with a link to a read-only copy of the paper, followed by the abstract.
Biodiversity is declining through human activities and urbanisation is often seen as a particular concern. Urban settings, however, provide diverse microclimatic conditions for plants and pollinating insects, and therefore may be significant habitats for the conservation of solitary and primitively eusocial bees, a major group of pollinators. This study analysed the interactions between these bees and the plants on which they forage, using a network approach. We compared urban habitats (gardens, roadsides, and open vegetation) in a large British town with nearby nature reserves. One native plant Taraxacum officinale (dandelion) was a core generalist species visited in all habitat types. Other core plant species restricted to particular habitats include species of Geranium, Bellis, Crepis, and Ranunculus. Two generalist bee species, Anthophora plumipes and Osmia bicornis were the core visitor species within the networks. The networks were comparatively more nested in urban habitat types than nature areas, suggesting more frequent interactions between generalist and specialist species in urban areas. Network connectance, network level specialisation (H2’ index), and plant generality (network level) were not significantly different in urban and nature areas. However, visitor generality was found to be significantly higher in urban gardens than in nature areas. Careful management of common urban vegetation would be beneficial for supporting urban wild pollinators.
One of the projects with which I’ve been involved over the past few years has been a collaboration with researchers at Imperial College and the Natural History Museum, alongside regional collections in the UK, to assess how museum specimens of bumblebees (Bombus spp.) can be used to look at long-term ecological changes in pollinator populations. The first two papers from that project were published in August but because of my trip to Kenya I’ve only now been able to post about them.
The details of the papers (both of which are open access and free to download) are below, followed by the official press release:
Arce, A., Cantwell-Jones, A., Tansley, M., Barnes, I., Brace, S., Mullin, V., Notton, D., Ollerton, J., Eatough, E., Rhodes, M., Bian, X., Hogan, J., Hunter, T., Jackson, S., Whiffin, A., Blagoderov, V., Broad, G., Judd, S., Kokkini, P., Livermore, L., Dixit, M., Pearse, W. & Gill, R. (2022) Signatures of increasing environmental stress in bumblebee wings over the past century: Insights from museum specimens. Journal of Animal Ecology 00, 1– 13. https://doi.org/10.1111/1365-2656.13788
Mullin, V. E., Stephen, W., Arce, A. N., Nash, W., Raine, C., Notton, D. G., Whiffin, A., Blagderov, V., Gharbi, K., Hogan, J., Hunter, T., Irish, N., Jackson, S., Judd, S., Watkins, C., Haerty, W., Ollerton, J., Brace, S., Gill, R. J., & Barnes, I. (2022). First large-scale quantification study of DNA preservation in insects from natural history collections using genome-wide sequencing. Methods in Ecology and Evolution, 00, 1– 12. https://doi.org/10.1111/2041-210X.13945
OFFICIAL PRESS RELEASE: Museum collections indicate bees increasingly stressed by changes in climate over the past 100 years
• An analysis of bumblebee wings from a network of UK museums shows signs of stress linked to increasingly hotter and wetter conditions. • As well as revealing what is linked to stress in bees in the past, the study can help predict when and where bees will face most stress and potential decline in the future. • Bumblebees and other insect pollinators have faced population declines in recent years. • The researchers have also for the first time used ancient DNA techniques to sequence bumblebee genomes dating back over 100 years. Scientists from Imperial College London and the Natural History Museum today published two concurrent papers analysing UK bumblebee populations.
The first investigated the morphology (body shapes) of bee specimens dating back to 1900. Using digital images, the group first investigated the asymmetry in bumblebee wings as an indicator of stress. High asymmetry (very differently shaped right and left wings) indicates the bees experienced stress during development – an external factor that affected their normal growth.
Studying four UK bumblebee species, the group found evidence for stress getting higher as the century progressed from its lowest point around 1925. Further analysis showed that each bee species displayed a consistently higher proxy of stress in the latter half of the century.
Learning from the past to predict the future By taking the climate conditions during the year of collection – namely annual mean temperature and annual rainfall – the team found that in hotter and wetter years bees showed higher wing asymmetry. The study is published today in the Journal of Animal Ecology.
Author Aoife Cantwell-Jones, from the Department of Life Sciences (Silwood Park) at Imperial, said: “By using a proxy of stress visible on the bee’s external anatomy and caused by stress during development just days or weeks before, we can look to more accurately track factors placing populations under pressure through historic space and time.”
Author Dr Andres Arce, now at the University of Suffolk, stated: “Our goal is to better understand responses to specific environmental factors and learn from the past to predict the future. We hope to be able to forecast where and when bumblebees will be most at risk and target effective conservation action.”
Senior author Dr Richard Gill, from the Department of Life Sciences (Silwood Park) at Imperial, said: “With hotter and wetter conditions predicted to place bumblebees under higher stress, the fact these conditions will become more frequent under climate change means bumblebees may be in for a rough time over the 21st century.”
DNA from a single leg As well as measuring the wing shapes of bees, in a second parallel study the team successfully sequenced the genomes of over a hundred bumblebee museum specimens dating back more than 130 years. In a pioneering advance, ancient DNA methods typically used for studying woolly mammoths and ancient humans, were for the first time used on an insect population.
Scientists from the Natural History Museum and the Earlham Institute quantified DNA preservation using just a single bee leg from each of the bees studied to create a baseline genome for each of the four species.
From these developments, published today in Methods in Ecology & Evolution, the researchers can now look to determine how the reported stress may lead to genetic diversity loss.
In conjunction with providing a new reference genome, the team will now use this data to study how bee genomes have changed over time, gaining an understanding of how whole populations have adapted – or not – to changing environments.
The value of museum collections Focusing on bumblebee collections, the team worked with curators from the Natural History Museum London, National Museums Scotland, Oxford University Museum of Natural History, World Museum Liverpool, and Tullie House Museum Carlisle.
Author Dr Victoria Mullin, from the Natural History Museum, said: “Museum insect collections offer an unparalleled opportunity to directly study how the genomes of populations and species have been affected by environmental changes through time. However, they are a finite resource and understanding how best to utilise them for genetic studies is important.”
Senior author Professor Ian Barnes, from the Natural History Museum, said: “One of the main problems with museum collections is that the quality of DNA can be very variable, making it difficult to predict which type of analyses we should do. We now have a much better idea about DNA preservation in insect collections, which is a massive boost to our ongoing work to understand the history and future of insect populations.”
Dr Gill concluded: “These studies showcase the value of leveraging museums specimens to go back in time and unlock the past’s secrets. But what we have done is just the beginning, and by continuing our work with these vital public collections and collaborating with curators we can only discover more. All this work was part of a Natural Environment Research Council-funded project and could not have been achieved without the commitment, hard work, and diligence of the museum curators, and our other collaborators”.
Prof. Jeff Ollerton - ecological scientist and author 