Introduced species shed friends as well as enemies – a new study published this week

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:

Xirocostas, Z.A., Ollerton, J., Peco, B., Slavich, E., Bonser, S.P., Pärtel, M., Raghu, S. & Moles, A.T. (2024) Introduced species shed friends as well as enemies. Scientific Reports 14: 11088

Here’s the abstract:

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.

A use for invasive Yellow-legged Hornets? – China Diary 4

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The UK media has fueled something of a moral panic over the last couple of years, in relation to the Yellow-legged Hornet (Vespa velutina) which has become established as an invasive species in Europe. It also looks likely to become established in Britain and Ireland, where beekeepers have claimed that it poses “a severe threat to pollinators“. The only study that I know of that’s tested this idea in Britain – by Thomas O’Shea-Wheller, Juliet Osborne, et al. – suggests that the impact on bumblebees, at least, is not as great as feared.

In Asia, where the species originates, they’ve lived with this hornet for centuries and learned to exploit it. On a visit to a recent farmer’s market near Kunming we encountered a local man selling bottles of adult hornets steeped in alcohol, to be used as a liniment. It’s rubbed on arthritic joints and (apparently) soothes the pain.

The guy who was selling the bottles of embrocation had several hornet’s nests on display:

Later, on a trip to Lijiang I also spotted a hornet’s nest on a building, not the usual place you expect to see one:

The other use for hornets is as food – the larvae are apparently quite delicious and very nutritious. This is from a different market and is a different species:

Later on the Lijiang trip we visited a farm that was part of a Yi community, one of the local ethnic minorities. They keep the indigenous honey bees (Apis cerana) in these small hives:

The honey bees pollinate an early-flowering local cherry variety that farmers grow in small orchards. The fruit is extremely small but also extraordinarily sweet:

These ones are past their best though still edible:

Much fresher cherries were being sold in farmer’s markets and at the roadside:

We’re still trying to work out what variety of cherry this is – possibly a landrace of the highly variable Chinese Cherry (Prunus pseudocerasus).

Of course, hornets can be pollinators too, though a study last year of the Yellow-legged Hornet in Spain showed that they negatively impact pollination of ivy in that region. These insects are definitely a cause for concern, though whether their impacts will be as great as some fear remains to be seen.

The mystery of what pollinates poinsettias – China Diary 3

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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…

I also discuss poinsettia, and specifically its pollination, in my recent book Birds & Flowers: An Intimate 50 Million Year Relationship – this is what I say in the chapter called ‘Urban flowers for urban birds’:

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.

Seeds have power far beyond their size – China Diary 2

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In the image above, the three glass tubes on the right contain different cultivated varieties of soybean (Glycine max), one of the world’s most important (and controversial) legume crops. The tube on the left contains the seeds of what is considered the wild ancestor of soybean (Glycine soja). Archaeological evidence suggests that by about 5,000 years ago farmers in several areas of Asia had artificially selected varieties that had much bigger seeds than the wild type. I like this image because it’s a great demonstration of the power of humans to positively influence the food that we eat – and the power of those seeds to affect us via our diets and farming methods.

Of course it’s not just soybean that’s been subject to this sort of artificial selection – we’re encountering many other species and varieties of beans at the various farmer’s markets we’re visiting here in Yunnan:

Many of these beans require pollinators such as bees to initiate or at least enhance the crop, as we found in our recent study of soybean as part of the SURPASS2 project.

I took the main image last week when I had a tour of the Germplasm Bank at the Kunming Institute of Botany, a really impressive facility that stores both seeds in deep freeze and living plants in tissue culture. It’s one of the ways in which we can help to conserve the genetic diversity of wild and cultivated plants. Here are a few more photographs from that visit:

Dr Jie Cai, the manager of the seed bank, kindly hosted the tour and introduced the facility:

Seeds are stored at about -20C in huge, security-controlled freezers:

Collected seeds are first cleaned, sorted, and then counted – a laborious task that requires patience:

Samples of seeds are also germinated at various points to assess how well they are responding to storage:

Plants with seeds that do not respond well to being stored, such as many orchids and bamboos, are grown in tissue culture:

The building also hosts the genetic sequencing facility, another extremely impressive set of laboratories in which progress of sequencing the Chinese flora can be seen in real time:

First footsteps in Kunming – China Diary 1

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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.

Using photographic mark-recapture to estimate population size, movement, and lifespan of a reintroduced butterfly – new study just published

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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:

Wildman, J.P., Ollerton, J., Bourn, N.A.D., O’Riordan, S. & McCollin, D., (2024) Using photographic mark-recapture to estimate population size, movement, and lifespan of a reintroduced butterfly. Biodiversity and Conservation (in press)

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.

Aggressive dominance of acacia floral resources by wild East African lowland honey bees – a new study just published

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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:

Kashulwe, S., Mngulwi, J. B., Karlsson, C., Pfeifer, L., & Ollerton, J. (2024) Aggressive dominance of acacia floral resources by wild east African lowland honey
bees. African Journal of Ecology 62, e13271. https://doi.
org/10.1111/aje.13271.

Here’s the abstract:

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.