Earlier this year I was invited by the editor of British Wildlife magazine to write a piece for their Changing Perspectives section about how odd Europe is when it comes to bird pollination. It’s based on one of the chapters in my book Birds & Flowers: An Intimate 50 Million Year Relationship.
If you subscribe to the magazine, it will appear in the August issue, though I’m happy to send a PDF to anyone who doesn’t subscribe (or has not read the book) – use the Contact Page. The main accompanying photograph is by one of my former students, Lisa King, who kindly allowed me to use it.
It’s very easy to get a fixed idea of what you think a particular group of plants ‘ought’ to look like, based on those that are most familiar to you from where you live. But exploring a good botanic garden always reveals surprises, as far as plant families are concerned. Willows (or osiers) provided me with a great example recently. Based on those that I am familiar with, I thought I had a pretty good idea of what to expect from the family Salicaceae, which includes not just willows (Salix spp.) but also aspens and poplars.
Then you encounter the trunk of a large tree that’s covered in vicious thorns that remind you of the rose family (Rosaceae) and particularly some species of cherries and plums, such as Blackthorn (Prunus spinosa). But it’s a big tree, larger than expected for that group, and the bark in particular doesn’t look right:
Fortunately, being a botanic garden, there’s a helpful label:
Lo and behold, it’s a member of the willow family! A species of Xylosma, quite a large genus of about 100 species, but not one with which I am familiar.
I encountered another example in the Chinese medicinal garden – a species of milkwort (Polygala). The milkworts that are native to Britain are low-growing, herbaceous species, not tall woody shrubs like this P. arillata. The rather legume-like flowers are familiar, but not displayed in these pendant inflorescences, laburnum style:
This wasn’t the biggest surprise of my China trip so far, however – how about these clusters of yellow-ish white, highly fragrant flowers, on a large (15 metre) tree? What family could it belong to?
Again, Rosaceae comes to mind, but it turns out that it’s in the borage or forget-me-not family (Boraginaceae):
Those last two species are a nice example of a general trends in plant families and genera, which often contain smaller, herbaceous species in cooler, more temperate parts of the world and larger, woody species at lower latitudes in the tropics and subtropics. Bamboos (which are of course woody grasses) are a good example – and we have encountered some spectacular specimens in the garden:
Of course there’s also some familiar species, including birds: how many Little Egrets can you spot in this picture?
Exploring botanic gardens are one of my favourite pastimes, it’s always worthwhile and, in the words of an old blog post of mine, Je ne egret rien.
I’m a long-standing fan of his YouTube video channel which Joey describes as “A Low-Brow, Crass Approach to Plant Ecology & Evolution as muttered by a Misanthropic Chicago Italian.”
It was a lot of fun to talk flowers and pollinators with him and although I tried to keep my swearing to a minimum, if you know Joey and his work, you know what you’re in for, so be warned! It’s not for the easily offended.
We had sound issues at a couple of points and note that at 54:20 I made an error, and said “hummingbirds” a couple of times when I meant “sunbirds”. Put it down to a lack of coffee that morning….
Walking into Kunming Institute of Botany yesterday morning, I passed a young guy who was carrying what I initially thought was a species of Orobanchaceae. I’ve a long-standing interest in the pollination ecology of these intriguing parasitic plants, so I stopped to have a chat. Turns out they were in fact orchids! Specifically, they were specimens of Gastrodia elata, one of the “potato orchids“, so named because those fat tubers are edible. They are widely used in South China – where they are known as Tianma, 天麻 – both as a food and medicinally. The tubers are eaten before the flowers are produced, and originally they were collected from the wild. But in the 1960s a Chinese botanist named Xuan Zhou discovered how to cultivate them and they are now grown in specialist nurseries. A fascinating account of the life of Xuan Zhou – “The Father of Gastrodia” – was published in the journal Plant Diversity last year, shortly after he died.
These orchids do not produce green leaves or stems, therefore they cannot photosynthesise. Instead, they gain all of their energy from a parasitic symbiotic relationship with a fungus – they are what is termed “myco-heterotrophic“. Most myco-heterotrophic plants have evolved from ancestors that were involved in mutualistic mycorrhizal relationships with fungi, in which the plant provides sugars to the fungus in return for mineral nutrients and water. In the case of Gastrodia elata, the fungus concerned is the non-mycorrhizal, wood-rotting Armillaria mellea. In the west we know this as Honey Fungus, a disease of trees and shrubs and the bane of many a gardener. This is also edible, incidentally, but best dried before cooking (and some have an intolerance to it, so take care).
I tweeted the photograph in a short thread just after taking it, and Stewart Nicol pointed me to a study of the orchid’s floral biology and pollination ecology in Japan by Naoto Sugiura. Turns out that, at least in the population which Naoto studied, the plant produces no nectar and deceives its pollinators, which are small bees, into visiting the flowers.
That’s why I’ve used the phrase “doubly-parasitic*” in the title of this post – the plant, it appears, parasitically exploits both the fungus from which it gains energy and the pollinators that ensure its reproduction. It’s (almost, but not quite) the flip side of “double mutualism” in which species provide two benefits for one another, e.g. the same bird is both a pollinator and a seed disperser of a particular plant, a phenomenon that I discussed in my recent book Birds & Flowers: An Intimate 50 Million Year Relationship.
But note the question mark in the title of this post. There’s an enormous amount that we don’t know about these myco-heterotrophic interactions and how they remain stable over the evolutionary history of the plant and the fungus. In order to be considered a parasite, by definition, an organism must have a negative impact on the reproductive fitness of its host. Do these orchids negatively impact either the fungus or the bees that pollinate it? As yet we don’t know. And I was intrigued by this comment from a 2005 review of ‘The evolutionary ecology of myco-heterotrophy‘ by Martin Bidartondo:
“no successful plant lineage would be expected to cheat both mycorrhizal fungi (by failing to provide photosynthates) and deceive insect pollinators (by failing to provide nectar or other rewards) due to the evolutionary instability inherent to specializing on two lineages.”
At first glance it appears that Gastrodia elata is a plant lineage that has done just that, though I’d like to see more work carried out on this system. Specifically, are all populations of the orchid bee pollinated and are all rewardless? And does this orchid really provide no benefit to the fungus, perhaps by synthesising secondary compounds that protect the Armillaria from infection by bacteria or being eaten by invertebrates. So many questions to be answered about this fascinating species interaction!
*With thanks to my wife Karin Blak for inspiring that phrase.
As I’ve previously discussed on the blog, when species are moved to a different part of the world they lose many of the ‘enemies’ – such as predators, herbivores and pathogens – that would normally keep their populations in check. This can have implications for the likelihood of a species becoming invasive, and it’s called the Enemy Release Hypothesis (ERH) and has been well studied. Less well researched is the flip side of the ERH, the Missed Mutualist Hypothesis (MMH), in which species lose their ‘friends’, such as pollinators, seed dispersers, symbiotic fungi, and so forth. It’s a topic I’ve worked on with my colleagues at the University of New South Wales, principally Angela Moles and her former PhD student Zoe Xirocostas.
Another paper from Zoe’s PhD work has just been published and in it she carried out a comparison of European plants that have been transported to Australia, and asked whether they had fewer pollinators in their new range. It turns out that they do!
Here’s the full reference with a link to the paper, which is open access:
Many studies seeking to understand the success of biological invasions focus on species’ escape from negative interactions, such as damage from herbivores, pathogens, or predators in their introduced range (enemy release). However, much less work has been done to assess the possibility that introduced species might shed mutualists such as pollinators, seed dispersers, and mycorrhizae when they are transported to a new range. We ran a cross-continental field study and found that plants were being visited by 2.6 times more potential pollinators with 1.8 times greater richness in their native range than in their introduced range. Understanding both the positive and negative consequences of introduction to a new range can help us predict, monitor, and manage future invasion events.
Is it too early to talk about Christmas? Not if you’re interested in pollinators and pollination! The mid-winter festival has featured quite a number of times on my blog over the years, especially in relation to the iconic plants that represent this time of year in Northern Europe, and what one might describe as the ‘cultural biodiversity‘ of Christmas. The final plant that I included in that last post was the poinsettia (Euphorbia pulcherrima) – this is how I described it:
In many ways this is an unusual plant to have such a strong cultural association with Christmas: it’s a mildly toxic species of spurge from tropical Mexico that was introduced to North America in the 19th century, then subsequently to Europe. However its festive connotations date back to the earliest period of Spanish colonisation in the 16th century, so it’s older than some…other Christmasy traditions…
Just occasionally one sees a bird-pollinated tree planted in a city. The most common in my experience are various banksias in Australia, and the Royal Poinciana (from Madagascar) and the African Tulip Tree in the urban tropics and subtropics elsewhere in the world. I’ve also occasionally encountered large specimens of Poinsettia: when they are given free rein they are a much more impressive plant than their Christmas cousins. The vivid red bracts that surround the clusters of flowers suggest that they may be hummingbird-pollinated in their native Central America, but as far as I know their pollination ecology has not been studied.
Here at the Kunming Botanic Garden there’s several quite large specimens of poinsettia that, as I write, are in full flower, their red bracts a signal to pollinators that can be seen for quite a distance. However we’ve not seen any of the local sunbirds or white-eyes visit the flowers, and, as I said in the book, as far as I know the pollination ecology of poinsettia has never been studied in the wild. Close inspection of the flowers in the garden revealed that almost all of the nectaries had at least one nectar-collecting ant sticking out from it, their prominent backsides a deterrent to the Asian Honey Bees (Apis cerana) that also wanted a piece of the action.
Based on the position of the nectaries in relation to the stamens, if the plant is hummingbird-pollinated then the pollen is likely to end up under the chin of the bird. That’s certainly been described in other plant-bird pollination systems. But it does not have to be birds that move the pollen around – red flowers are also associated with other kinds of pollinators, for example butterflies and beetles. But until someone in Mexico does the necessary field work, we’ll just have to speculate.
Just over a week ago I arrived in China to spend three months as a visiting professor at the Kunming Institute of Botany (KIB), of the Chinese Academy of Sciences. I am being hosted by my colleague Dr Zong-Xin Ren, and I will repeat this trip each year over the next three years. This is my first visit to Kunming because my last visiting professorship here had to be conducted remotely due to the COVID-19 pandemic. As you can see above, KIB is adjacent to, and works closely with, Kunming Botanical Garden and I have the good fortune of being able to walk to work each day through the gardens:
As I’ve said before, I love botanic gardens because I always, always see plants that amaze and surprise me. For example, I struggled to recognise the family that this very large tree belonged to – and was surprised by the answer!
I’ll be spending my time working on some data and writing manuscripts, carrying out field work, and talking with KIB postgrads and postdocs about their projects. I’ll also give some lectures here and at other institutions in China. The first of these was last Thursday where I spoke about the role of plant-pollinator interactions in underpinning the United Nations Sustainable Development Goals:
Thanks to Brazilian researcher Sinzinando ‘Nando’ Albuquerque-Lima for those last two photographs. As part of a Brazilian-funded project, Nando is here for about 8 months studying a range of plants and their pollinators.
Further afield, Zong-Xin and Nando have introduced me to some of the amazing markets and restaurants in the city and I’ve already added three new plant families to my life list of those I’ve consumed: Phyllanthaceae (the rather sour fruit of a Phyllanthus species); Alismataceae (deep-fried, ‘crisped’ roots of a Sagittaria species); and Meliaceae (the young leaves of Toona sinensis are used as a spinach):
That last photo does not show rhubarb! They are the stems of a variety of taro (Colocasia esculenta) an Araceae species. Yunnan is especially famous for its wild-collected fungi:
On Sunday afternoon Zong-Xin’s research group gave some presentations about their research, which is diverse and exciting and I look forward to discussing it with them some more in the coming months. The afternoon started with a talk by Zong-Xin himself about the history and opportunities of studying pollinators and pollination in China:
And then we all went to dinner!
That’s all for now, I’ll add updates as the weeks go by.
The reintroduction of the Chequered Skipper butterfly to England is one of the outstanding conservation success stories of the last ten years. I’ve been proud to play a part – see these old posts here, here and here – and in particular supervising Jamie Wildman’s PhD work. The second paper from his thesis has just been published and in it Jamie documents how you can identify individual butterflies by their markings and use this information to estimate the population size, life-span, and movements of Chequered Skippers. The technique could also be applied to other distinctively marked butterflies.
Here’s the reference with a link to a read-only version of the study:
If you need a PDF, get in touch via my Contact page.
Here’s the abstract:
The chequered skipper butterfly Carterocephalus palaemon was reintroduced to Fineshade Wood, England in 2018 as part of a Butterfly Conservation-led project following several years of planning. From 2019–2022, the population was sampled each May–June by the lead author, timed count volunteers, Butterfly Conservation staff, and casual observers.
A novel photographic mark-recapture (PMR) technique was trialled as an alternative to mark-release-recapture (MRR). In conjunction with timed counts, PMR was used to photoidentify individual C. palaemon through each butterfly’s upperside (ups) wing markings, estimate daily and gross population size, detect movements, and determine lifespan. As capture and recapture can be achieved non-invasively using PMR, habitat disturbance, the potential to influence butterfly behaviour, accelerate wing wear, affect mate selection and predation, and heighten mortality risk through handling are eliminated. We found PMR to be a viable alternative to MRR for a sensitive reintroduction of a low-density species with unique ups markings such as C. palaemon. Using capture histories generated through PMR, from a known founder population size of 42 butterflies in 2018, we estimated the population at Fineshade Wood had increased to 618 butterflies (+ 1371.43%) by 2022.
Movements of up to 2.22 km over a time period of 17 days were also detected. Lastly, we discuss the implications of PMR for population sampling of other Lepidopterans, and the potential to improve cost-efficiency of the technique using machine-based learning tools.
Back in August 2022, Karin and I traveled to Kenya where I was teaching on a Tropical Biology Association field course at the Mpala Research Centre – see my posts from the time here and here.
Students on the course have to complete an extended group project, with supervision by teaching staff. Two of the groups looked at the visitors to flower heads of one of the dominant savannah acacias and the interactions between wild honey bees of the native subspecies and the other insects. There have been rather few studies of this honey bee in the wild and so we wrote up the work as a short research note that has now been published in the African Journal of Ecology.
The photo above shows the authors – ‘Team Etbaica’ – from left to right: Luis Pfeifer, Swithin Kashulwe, me, Caka Karlsson, and Janeth Mngulwi.
Here’s the reference with a link to the publisher’s site – the paper is open access:
The East African lowland honey bee (Apis mellifera scutellata) is reported as an aggressive subspecies of the Western honey bee, but few studies have investigated the impact of its aggressiveness on other insect pollinators. Observations of flower visitors to Vachellia (Acacia) etbaica and interactions between honey bees and other insects were conducted in 2022 in Mpala, Kenya. A total of 873 individual flower visitors were recorded, the most frequent being Hymenoptera, followed by Diptera and Lepidoptera. Honey bees dominated floral resources in the morning and late afternoon. When honey bees encountered other types of insects, they displaced the latter from flowers 100% of the time. This has never been observed in other Western honey bee subspecies, and we recommend further research on these taxa.
During the 2020 lockdown caused by the COVID-19 pandemic, I coordinated an international network of pollination ecologists who used standardised methods to collect data in their gardens. I blogged about it at the time – see here and here for instance – and also put up a post when the data paper from that work was published.
Several research groups are now working with that huge data set and interrogating it for answers to a wide range of questions. The first group to actually publish a paper from the data is a largely Chinese set of researchers from the Key Laboratory of Plant Resources, Conservation and Sustainable Utilization, at the South China Botanical Garden in Guangzhou, assisted by Kit Prendergast and myself.
In this paper we’ve considered how robust these plant-pollinator networks are to simulated extinctions of species, and how this is affected by the elevation, latitude, and plant species diversity of the network.
Here’s the full reference with a link to the study:
If you can’t access it and need a PDF, please send me a request via my Contact page.
Here’s the abstract:
Plant-pollinator interactions play a vital role in the maintenance of biodiversity and ecosystem function. Geographical variation in environmental factors can influence the diversity of pollinators and thus, affect the structure of pollination networks. Given the current global climate change, understanding the variation of pollination network structure along environmental gradients is vital to predict how global change will affect the ecological interaction processes. Here, we used a global plant-pollinator interaction data collection by the same sampling method at the same period to explore the effects of elevation, latitude, and plant richness on the structure and robustness of pollination networks. We analyzed a total of 87 networks of plant-pollinator interactions on 47 sites from 14 countries. We conducted a piecewise structural equation model to examine the direct and indirect effects of elevation, latitude, and plant richness on the network robustness and analyzed the function of network structure in elucidating the relationship between robustness and these gradients. We found that plant richness had both positive effects on robustness under random and specialist-first scenarios. Elevation, latitude, and plant richness affected network connectance and modularity, and ultimately affected network robustness which were mediated by nestedness under specialist-first and random scenarios, and by connectance under the generalist-first scenario. This study reveals the indirect effects of elevation, latitude, and plant richness on pollination network robustness were mediated by nestedness or connectance depended on the order of species extinctions, implying that communities with different pollination network structures can resist different extinction scenarios.
Prof. Jeff Ollerton - ecological scientist and author 