Biodiversity Net Gain is generating a lot of attention in the UK at the moment, some of it positive*:
“when designed and delivered well, BNG can secure benefits for nature, people and places, and for the economy”
“[BNG is] a game-changer for health and wellbeing”
And some of it extremely negative*:
“Biodiversity Net Gain is a lie but most people without enough ecological knowledge cannot see this & are fooled by the lie”
“[BNG is] a horrible legalistic contrivance, and it means nothing”
Regardless of how you feel about BNG, it’s here to stay, at least for the foreseeable future, and so we need to explore it and understand how (or whether) it can positively improve the state of nature in Britain.
Although I don’t pretend to be an expert on BNG**, I have thought a lot about how it might impact the group that I do have some expertise in, pollinators, and the implications for the pollination services that they provide to wild and crop plants.
Last October I produced a short report that considered the implications of BNG for insect pollinators – you can download a copy from the original blog post, though do be aware that some of the dates I mentioned were later revised by the then government and I have yet to revise the document.
As a follow up to this I have been invited by the Biological Recording Company to lead a one-hour webinar discussing this topic on Monday 28th October at 1pm. It’s free to attend and you can book a ticket by following this link. There’ll be a short presentation (30 minutes or so) followed by a live Q&A.
I hope that some of you can join me!
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*Real quotes, culled from reports and social media.
**Indeed, it’s such a new approach to development and nature conservation, can anybody consider themselves an expert?
The most globally significant groups of pollinators are well known and have been studied for a long time: bees and wasps, flies, butterflies and moths, birds, bats and beetles are all familiar to those of us with an interest in pollination ecology. However, every few years a new type of pollinator or a novel pollination system is described from nature or from the fossil record, or we add further examples of previously neglected pollinator groups such as cockroaches.
This begs the question: how much is there still to discover? How close are we to describing the full diversity of animals that act as pollen vectors? Can looking at the past help us to predict what we might find in the future? That’s the topic of a Perspective article that I was invited to write for the special issue of the Journal of Applied Entomology on the theme of The Neglected Pollinators that I mentioned last month. It’s a subject that I’ve thought about a lot over the last few decades and it was great to get an opportunity to air some ideas and speculation.
The article is open access and you can download a copy by following the link in this reference:
Although huge progress has been made over the past 200 years in identifying the diversity of pollinators of angiosperms and other plants, new discoveries continue to be made each year, especially in tropical areas and in the fossil record. In this perspective article I address the following questions: Just how diverse are the pollinators and what are the phylogenetic limits to that diversity? Which other groups of animals, not currently known to regularly engage with flowers, might be found to be pollinators in the future? Can we predict, from the fossil record and from discoveries in under-researched parts of the world, which animal groups might turn out in the future to contain pollinators? I also discuss why adding to our knowledge of plant–pollinator interactions is important, but also stress that an incomplete knowledge may not be a bad thing if it means that remote, inaccessible and relatively pristine parts of the world remain that way.
Just after I arrived in Northampton in 1995, I set about looking for suitable local sites for conducting pollination ecology field work for myself and students. The campus on which we were situated at the time was adjacent to an urban park – Bradlaugh* Fields – parts of which were designated as local nature reserves. In the intervening years, data from that area have made their way into a wide range of published studies, including:
I still have data collected during that time that have never been published, but good data are hard won and they may see the light of day at some point. Case in point is that we’ve just published a paper based on data from Bradlaugh Fields, the first of which were collected in 2001!
In this paper we’ve tested how effective hoverflies, butterflies and bumblebees are at pollinating the flowers of a common generalist grassland plant, colloquially called Field Scabious (Knautia arvensis). The expectation was that bumblebees, being generally larger, hairier and more flower-focused than the other groups, would be the most effective at transferring pollen to stigmas. To our surprise, they were not: hoverflies and butterflies performed just as well! In fact we argue that butterflies may be MORE important as pollinators of this plant because they fly further distances between individual plants, rather than hopping between the inflorescences of the same plants, as bumblebees tend to do.
Crucially, the importance of these different groups of pollinators varies enormously as the relative abundance of the insects visiting the flowers differs between seasons. In some years butterflies dominate as pollinators, in other years bumblebees or hoverflies. This is driven, we think, both by fluctuations in the populations of these insects and by the availability of other, more preferred flowers that may bloom at the same time.
The paper is part of a special issue of the Journal of Applied Entomology devoted to The Neglected Pollinators. It’s open access and you can download a copy by following the link in this reference:
Plant-pollinator interactions exist along a continuum from complete specialisation to highly generalised, that may vary in time and space. A long-held assumption is that large bees are usually the most effective pollinators of generalist plants. We tested this by studying the relative importance of different groups of pollinators of Knautia arvensis (L.) Coult. (Caprifoliaceae: Dipsacoideae). This plant is suitable for such a study because it attracts a diversity of flower visitors, belonging to different functional groups. We asked whether all functional groups of pollinators are equally effective, or if one group is most effective, which has been documented in other species with apparently generalised pollination systems. We studied two subpopulations of K. arvensis, one at low and one at high density in Northampton, UK. To assess pollinator importance we exposed unvisited inflorescences to single visits by different groups of pollinators (butterflies, bumblebees, hoverflies and others) and assessed the proportion of pollinated stigmas. We then multiplied the effectiveness of each pollinator group with their proportional visitation frequency in five different years. For each group we also compared time spent on flowers and flight distance between visits. The relative importance of each pollinator group varied between years, as did their flight distances between flower visits. Butterflies were the best pollinators on a per visit basis (in terms of the proportion of stigmas pollinated) and flew further after visiting an inflorescence. Different measures and proxies of pollinator effectiveness varied between taxa, subpopulations, and years, and no one group of pollinators was consistently more effective than the others. Our results demonstrate the adaptive value of generalised pollination strategies when variation in relative abundance of different types of pollinators is considered. Such strategies may have buffered the ability of plants to reproduce during past periods of environmental change and may do so in the future.
Later this month I’ve been invited by the Oxford Ornithological Society to give a talk about my new book Birds & Flowers: An Intimate 50 Million Year Relationship. The talk will summarise the main themes from the book, particularly the sheer diversity of birds that can act as pollinators, what it means for the ecology and evolution of flowers, why the conservation of such interactions matters, and the cultural significance of bird-flower interactions. I’ll also deal with the question of why Europe is so odd when it comes to the question of birds as pollinators.
The talk is on Wednesday 11th September at Exeter Hall, Kidlington, starting at 7.45 pm; it’s free to society members, and non-members are invited to make a donation. Do come along if you’re in the area!
The latest paper from Muzafar Sirohi‘s PhD work on urban solitary bees has just been published in the journal Zoodiversity, a publication of the National Academy of Sciences of Ukraine. In this paper we looked at how the flight periods of urban populations of bees differ from those in surrounding nature reserves and other “natural” settings. One of the most interesting findings is that urban bees tend to emerge earlier, and be active longer, than their rural counterparts. The quote the study:
“We observed a substantial effect of urban microclimate on bee flight periods. A total of 153 individuals of nine bee species were recorded one to nine weeks before or after their expected flight periods. In contrast, only 14 individuals of four species were seen at unusual flight periods in nature sites.”
In my book Pollinators & Pollination: Nature and Society I discussed the importance of towns and cities for supporting pollinator populations, and conversely how important those populations are for urban food production. Likewise, in Birds and Flowers: An Intimate 50 Million Year Relationship I have a chapter entitled “Urban flowers for urban birds”. The relationship between our built environment and pollinators is a fascinating topic, but there’s still much we don’t understand about how these insects and vertebrates respond behaviorally to urbanisation. Are they adapting in an evolutionary sense, or simply responding flexibly to the different conditions that cities impose on their biologies? Will future climate change make towns and cities uninhabitable for these animals? Hopefully our paper will stimulate further work on these and other topics.
Here’s the full reference with a link to the paper (which is open access):
Solitary and primitively eusocial bees, an important group of pollinators, have declined in the past few decades. In view of the recent focus on safeguarding pollinating insects, it is vital to understand the basic ecology of species for their conservation, for example their phenologies. We observed the flight periods of solitary and primitively eusocial bees in both the urban core of a large British town and nearby nature conservation areas. The bee surveys were conducted with standardised methods, on warm sunny days from the first appearance of bees in March 2012 and continued until October 2012. This study confirmed that a high number of species are active in the spring season. The emergence dates of species in urban areas and nature sites varied; about 26 of the 35 species were recorded at least one week earlier in urban areas; in contrast, only four species were seen earlier in nature conservation sites. When comparing this with the expected flight periods recorded (largely in nature sites) in the literature, many species were recorded at their expected time. However, a few individuals were recorded after their usual flight activity time, suggesting that the populations were possibly affected by the microclimate in urban areas. More urban phenological data are needed to understand the phenological trends in bees in urban habitats.
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.
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.
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:
Prof. Jeff Ollerton - ecological scientist and author 