Category Archives: Apocynaceae

A new study shows that even short-tubed flowers can specialise on hawkmoths as pollinators

Of all of the “classical” pollination syndromes, flowers that are hawkmoth pollinated have one of the highest levels of predictability. If a flower is pale in colour, opens at night, is highly scented, and possesses a long tube at the bottom of which is a supply of nectar, there’s a very high likelihood that it’s pollinated by long-tongued hawkmoths (Sphingidae).

Indeed, one of the foundational stories about the development of our understanding of how pollination systems evolve, relates to Charles Darwin, the long-tubed orchid Angraecum sesquipedale and the hawkmoth Xanthopan morganii praedicta.

Fast forward 160 years and we now know that pollination syndromes are more complex than 19th and early 20th century scientists imagined – see my recent book Pollinators & Pollination: Nature and Society for a discussion of this topic. That’s not surprising because, as I point out, we probably have data on the interactions between plants and their pollinators for only about 10% of the estimated 352,000 species of flowering plants. There’s still much to be discovered!

As an example of how our understanding of specialised flower-hawkmoth interactions is developing, consider this recent study that I’ve just published with my Brazilian colleague Felipe Amorim and other collaborators. In it we have shown that, contrary to expectations, a species of Apocynaceae (Schubertia grandiflora) with a relatively short floral tube can specialise on hawkmoths with much longer tongues than we might predict.

The full reference with a link to the study is shown below, followed by the abstract. If you would like a PDF, please drop me a line via my Contact page:

Amorim, F.W., Marin, S., Sanz-Viega, P.A., Ollerton, J. & Oliveira, P.E. (2022) Short flowers for long tongues: functional specialization in a nocturnal pollination network of an asclepiad in long-tongued hawkmoths. Biotropica https://doi.org/10.1111/btp.13090

Abstract:

Since Darwin, very long and narrow floral tubes have been known to represent the main floral morphological feature for specialized long-tongued hawkmoth pollination. However, specialization may be driven by other contrivances instead of floral tube morphology. Asclepiads are plants with a complex floral morphology where primary hawkmoth pollination had never been described. We detailed here the intricate pollination mechanism of the South American asclepiad Schubertia grandiflora, where functional specialization on long-tongued hawkmoth pollinators occurs despite the short floral tube of this species. We studied two plant populations in the Brazilian Cerrado and recorded floral visitors using different approaches, such as light-trapped hawkmoths for pollen analysis, direct field observations, and IR motion-activated cameras. Finally, using a community-level approach we applied an ecological network analysis to identify the realized pollinator niche of S. grandiflora among the available niches in the pollinator community. Throughout a period of 17 years, long-tongued hawkmoths were consistently recorded as the main floral visitors and the only effective pollinators of S. grandiflora. Flowers rely on highly modified corona and gynostegium, and enlarged nectar chambers, to drive visitors and pollination mechanism. Despite its relative short-tube, network analysis placed S. grandiflora in the module including exclusively long-tongued hawkmoth pollinators and the most phenotypically specialized sphingophilous plants in the community. These results represent the first example of functional specialization in long-tongued hawkmoths in an asclepiad species. However, this specialization is uncoupled from the long floral tubes historically associated with the sphingophily syndrome.

Generating AI art from titles of scientific publications

WARNING: huge time wasting potential ahead.

As regulars to my blog might know, I’m a sucker for computer-generated “stuff”, for example virtual ecological systems; see my 2020 post “a simple online ecosystem model: like Tamagotchi for the green generation“. Last night while browsing Twitter I came across a few people tweeting about app.wombo.art which uses words and phrases as a prompt for its AI to generate art in a variety of styles. For example, the image above is based on the title of my book Pollinators & Pollination: Nature and Society. The downloaded image always has “dream” at the top which is easy enough to crop, while “PROMPT” is the word or phrase that you entered, which can be turned off.

You can also use the titles of scientific articles – this one is my 1996 paper “Generalization in Pollination systems and Why it Matters” (I don’t think that it counts as a graphical abstract…):

A lot of people were submitting their thesis titles and I expect to see some of these used as frontispieces in PhDs in the near future. Here’s mine (from 1993) – “Ecology of flowering and fruiting in Lotus corniculatus“:

The other category that I had fun with was using scientific names – here’s the genus Ceropegia:

And here is Apocynaceae:

Can you guess what phrase I used to generate this one:

What’s really fascinating about this system is that every time you generate an image from the same phrase it returns something different. Go have fun, but be warned: it’s a bit of a rabbit hole and it’s possible to waste a lot of time playing around:

A milkweed on the shore: tracking down an elusive Danish plant

Since arriving in Odsherred towards the end of August I’ve been looking out for one plant in particular on our bicycle rides and hikes around the region. Vincetoxicum hirundinaria is a widespread asclepiad or milkweed: a member of the family Apocynaceae, subfamily Asclepiadoideae. This is a group of plants on which I’ve published quite a few research papers and which feature heavily in my book Pollinators & Pollination: Nature and Society.

So far the species has proven elusive and a few Danish ecologists that I’d spoken with told me they had never seen it in the wild. The GBIF account of the species shows a few populations in this part of Denmark but I wasn’t sure if they were old records of populations that no longer exist. But as of yesterday I can confirm that at least one of those populations is extant!

We had cycled out to the small town of Klint about 13km west of us, to see the glacial moraine landscape for which the area is famous and which gives Odsherred UNESCO Geopark status. As we approached the small fishing harbour at Klint I let out an excited shout to Karin who was just ahead of me: in amongst the roadside vegetation I’d spotted the distinctive and immediately recognisable yellow of Vincetoxicum hirundinaria in its autumnal hues! In the photos that follow you can see how well that yellow stands out against the colours of the other plants in the community.

At this time of the year the plant has ceased flowering, but the occasional swollen green seed pod was evidence of successful pollination of their morphologically complex flowers.

I was surprised at just how close to the sea the plants were growing; they must get inundated by sea water during stormy tidal surges.

So what is pollinating these flowers on this exposed shoreline? That’s a question that I want to pursue in the coming years. The Pollinators of Apocynaceae Database has remarkably few records of pollinators in this species, given how widespread it is. Flies certainly pollinate it, but there’s also records of wasps and bees as visitors, including bumblebees on flowers of a plant that I had in cultivation in Northampton. There’s a couple of other research groups in Scandinavia and Europe who are looking at the pollination ecology of the species and I’m hoping that we can collaborate on a study of spatial variation in its reproduction. Vincetoxicum is quite a large genus (around 150 species) and only around 10% of the species have been studied in any detail. But these studies are revealing a complex diversity of pollinators, including most recently, cockroaches in the Chinese species Vincetoxicum hainanense. I’m sure this intriguing group of plants has more fascinating stories to tell us about the ecology and evolution of its pollination systems.

FIGURE 4 from Xiong et al. (2020) Specialized cockroach pollination in the rare and
endangered plant Vincetoxicum hainanense in China. American Journal of Botany 107:
1355–1365.

The largest West African flower: Pararistolochia goldieana!

Some years ago, browsing in a second hand bookshop, I happened across a copy of an old magazine from 1950 called Nigeria. Published by the then colonial government, it was a miscellaneous collection of articles about the culture, geography and natural history of that fascinating West African country. Although aspects of the contents are problematical by modern standards, I bought it because of a short article about a wild plant with enormous flowers and a remarkable pollination strategy. In particular, the spectacular photograph of a man holding a flower that’s the length of his forearm grabbed my attention: who couldn’t love a flower like that?!

The plant is Pararistolochia goldieana, a vine found in the forests of this region, as described in the introductory text:

These types of flowers are pollinated by flies, a common strategy in the Birthwort family (Aristolochiaceae) to which the plant belongs. This strategy of fly pollination in which flies are deceived into visiting the flowers by their stink and colour, and temporarily trapped in the enclosed chamber, is something that I explore in detail in my book Pollinators & Pollination: Nature and Society, particularly in the genus Ceropegia. Those plants show convergent evolution with the pollination systems of Aristolochiaceae, though they are unrelated.

Pararistolochia goldieana has a wide distribution across West Africa, including Cameroon, Equatorial Guinea, Nigeria, and Sierra Leone. The IUCN Red List categorises it as ‘Vulnerable’ due to habitat loss. The population where these photographs were taken is described on the final page of the article:

The city of Ibadan is one of the largest in Nigeria and has grown enormously, ‘from 40 km2 in the 1950s to 250 km2 in the 1990s‘. I wonder if this forest, and its botanical treasures, still exists?

During field work in Gabon in the 1990s I was fortunate enough to encounter a species of Pararistolochia in the rainforest of Lopé National Park. It was a different species to P. goldieana, with rather smaller but no less spectacular flowers, and it stank to high heaven! We knew it was there long before we saw it. I collected some flies from the flowers and had them identified, though I’ve never published the data: it’s available if anyone is working on a review of pollination in the family.

This 1950 article is anonymous, so I don’t know who to acknowledge for the amazing images. However the botanist R.W.J. Keay was working on a revision of the family for the Flora of West Tropical Africa project at the time, so it may have been written by him.

A spectacular new plant has been named to honour a colleague: meet Ceropegia heidukiae!

Finding organisms that have not previously been described by scientists is not unusual; every year, hundreds of ‘new’ species enter the taxonomic literature, a testament to how little we still understand about the Earth’s biodiversity. The majority of these species are insects, because that’s the most diverse group of organisms on the planet. But new species of plants and fungi also turn up regularly: for example in 2020, botanists and mycologists at Kew named 156, including some from Britain.

So although discovering undescribed species is not uncommon, any field biologist will tell you that it’s an exciting moment to spot something that you’re never seen before and which could turn out to be new. That was certainly the case when my colleague Dr Annemarie Heiduk’s attention was drawn to a South African plant that was clearly something special. As Anne said to me this week:

‘I will never ever forget the very moment when I spotted it and immediately knew it was something no-one has ever seen before. And I was so lucky to find it in flower. I cannot describe how beautiful it looked sticking out of the surrounding grass vegetation. It is certainly one of a kind and I really know how lucky I was to have found it. Not once did it ever cross my mind that I will discover a novel Ceropegia species, let alone one that is so distinct!’

So it was that last year Anne discovered the plant that was to be named in her honour: Ceropegia heidukiae. The species has been described by David Styles and Ulrich Meve in the journal Phytotaxa (from where the image above was taken). There’s also an account of the species on the Pollination Research Lab blog, with further photographs and information about the plant.

Anne has been honoured in this way not just because she discovered the plant, but also because, to quote the paper, she:

‘is a pollination ecologist who with her research on the floral chemistry and deceptive pollination strategies of Ceropegia trap flowers has acquired recognition as an expert in this field’

Anne tells me that she has already collected pollinator and floral scent data for this new species, so we can look forward to seeing that published in the near future. I described the fascinating pollination ecology of Ceropegia, including some of Anne’s earlier work, in my recent book. This is a genus of plants that has intrigued me since I first saw photographs of them and started growing them as a teenager, 40 years ago. Since then I’ve published several papers about their pollination strategies, and how they compare with the family Apocynaceae as a whole: see the following links for some examples:

https://jeffollerton.co.uk/2017/09/03/fly-pollination-in-the-trap-flower-genus-ceropegia-a-new-study-just-published/

https://jeffollerton.co.uk/2018/08/21/the-evolution-of-pollination-systems-in-one-of-the-largest-plant-families-a-new-study-just-published-download-it-for-free/

So, a big congratulations to Anne, and to David and Ulrich – it’s an amazing plant! I wonder what else is still waiting to be discovered in the stunning grasslands of South Africa?

Flowers can be assholes – quite literally!

2003-572 s G Bochum

WARNING: There’s a high yuck factor to this post, it’s not for the squeamish or easily offended!

One of my Twitter contacts, Traci Birge in Finland, has been reading Pollinators & Pollination: Nature and Society, and making some very nice comments about it. I had to laugh at this one in which she describes some plants as “assholes” because of the way in which they deceive pollinators into visiting their flowers but offer no reward in return:

If you follow that thread you can see that Traci was closer to the truth than perhaps she realised: there are some plants with flowers that appear to mimic the anuses of dead mammals, particularly in the families Apocynaceae and Araceae. By their smell, texture, colour and hairiness they are fooling flies into visiting the flowers, because assholes, like any mammalian orifice, provide an entry point for maggots of carrion-feeding flies. Sometimes the deception is so great that the flies lay their eggs on these blooms, though of course the maggots starve.

A great example of an anus-mimicking bloom is the Dead Horse Arum (Helicodiceros muscivorus). Check out the image above: if that doesn’t look like a horse’s ass, I don’t know what does!

Other examples might be found within the stapeliads, especially the genus Huernia which often have a thickened annulus to the centre of the flower. However that could also be interpreted as mimicking an open, inflamed wound on the side of an animal:

As I point out in the book, you might imagine that there would be strong natural selection against flies visiting these flowers if they lose fitness by laying eggs on such an unsuitable substrate. But the flowers are tapping into really deep-seated behaviours and clearly the flies can’t distinguish the flowers from the real thing.

This is flower pollination that is far removed from the deliciously perfumed, cute-and-cuddly, heart-warming world of bees and flowers. Isn’t nature wonderful?

All photos from Wikipedia, as follows:

Helicodiceros muscivorus: Göteborgs botaniska trädgård (photographer: Ingemar Johansson) – http://www.mynewsdesk.com/se/pressroom/goteborgs_botaniska_tradgard/image/view/dracunculus-muscivorus-128973, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=19265330

Huernia zebrina: Enzo^ – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=10963668

Huernia schneideriana: Juan Carlos Fonseca Mata – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=94705877

Cockroaches as pollinators: a new example just published

When you think of the word “pollinator” what comes to mind? For most people it will be bees, particularly the western honeybee (Apis mellifera). Some might also think of hoverflies, butterflies, moths, bats, hummingbirds…..but cockroaches?! The first published example that I know of which demonstrated that the flowers of a plant are specialised for cockroach pollination is from the mid-1990s. Since then only a handful of well documented cases have come to light, but there are undoubtedly more out there waiting to be discovered, particularly in the wet tropics. Most of the c. 4,600 species of cockroaches are nocturnal, and cockroach-pollinated flowers tend to open at night, which is one reason why they are under documented.

In a new study, published this week in the American Journal of Botany, a team of Chinese, German and British biologists has shown that a species of Apocynaceae from China is the first known example of cockroach pollination in that large family. Here’s the reference with a link to the study; if anyone wants a copy please email me:

Xiong, W., Ollerton, J., Liede-Schumann, S., Zhao, W., Jiang, Q., Sun, H. Liao, W. & You, W. (2020) Specialized cockroach pollination in the rare and endangered plant Vincetoxicum hainanense (Apocynaceae, Asclepiadoideae) in China. American Journal of Botany (in press)

The abstract for the paper follows:

Premise

Species of Apocynaceae are pollinated by a diverse assemblage of animals. Here we report the first record of specialized cockroach pollination in the family, involving an endangered climbing vine species, Vincetoxicum hainanense in China. Experiments were designed to provide direct proof of cockroach pollination and compare the effectiveness of other flower visitors.

Methods

We investigated the reproductive biology, pollination ecology, pollinaria removal, pollinia insertion, and fruit set following single visits by the most common insects. In addition, we reviewed reports of cockroaches as pollinators of other plants and analyzed the known pollination systems in Vincetoxicum in a phylogenetic context.

Results

The small, pale green flowers of V. hainanense opened during the night. The flowers were not autogamous, but were self‐compatible. Flower visitors included beetles, flies, ants and bush crickets, but the most effective pollinator was the cockroach Blattella bisignata, the only visitor that carried pollen between plants. Less frequent and effective pollinators are ants and Carabidae. Plants in this genus are predominantly pollinated by flies, moths and wasps.

Conclusions

Globally, only 11 plant species are known to be cockroach‐pollinated. Because their range of floral features encompass similarities and differences, defining a “cockroach pollination syndrome” is difficult. One commonality is that flowers are often visited by insects other than cockroaches, such as beetles, that vary in their significance as pollinators. Cockroach pollination is undoubtedly more widespread than previously thought and requires further attention.

Is it safe to use oleander to treat COVID-19 symptoms?

No, it’s not safe. It’s a really, really dumb idea. Oleander is VERY poisonous and you could die. Do not do it.

OK, that was the short version; here’s the longer version. Oleander (Nerium oleander) is a plant belonging to the plant family that’s been the focus of much of my research for the past 30 years: Apocynaceae. The plant is widely grown in warm temperate and subtropical areas as an ornamental shrub or small tree and there are cultivars with flowers in a diverse palette of colours. In the Mediterranean, where it’s native, it’s a pollination generalist and pollinated by large bees, hawkmoths, and small flies. However, visitation to flowers is infrequent because, as Javier Herrera showed in this study, the flowers produce no nectar. It’s a rare example of a species of Apocynaceae with rewardless flowers in a family with very diverse pollination systems, as we showed in our study last year.

Although it’s very beautiful, oleander is also extremely poisonous. Many members of the family Apocynaceae are toxic: they are crammed full of alkaloids, cardiac glycosides, and other nasty chemicals that defend the plant against all but the most specialised of herbivorous insects, such as monarch butterflies (Danaus plexippus). But even in a family renowned for its toxicity, oleander stands out as being especially lethal.

Recently, a chemical derived from oleander called oleandrin has been touted as a health supplement to treat patients with the COVID-19 coronavirus. However there is no evidence that it is effective as a treatment but a LOT of evidence that it is highly toxic to both animals and humans. The fact that’s being touted as a COVID19 treatment by President Trump and some of his pharmaceutical industry donors should ring alarm bells for anyone with any common sense. And just because it’s a “natural” product does not in any way make it safe. DO NOT EAT OLEANDER!

Bound for the Great Southern Land

cropped-tenerife-2008-080

Great Southern Land, in the sleeping sun
You walk alone with the ghost of time
They burned you black, black against the ground
And they make it work with rocks and sand

Great Southern Land by Icehouse

Today Karin and I are packing before heading to the airport for a flight tomorrow to Australia.  It will be Karin’s first trip to the Great Southern Land, and my second: I spent part of 1993 and 1994 there on a short postdoctoral research project.

We’ll be there for about two months. Karin will be writing (she’s working on a book and will be contributing further articles to Medium and other outlets).  I’ll be working with Angela Moles and Stephen Bonser at the University of New South Wales (UNSW) on an Australian Research Council-funded project looking at whether species interactions affect the invasibility of plants native to Europe that are running wild in Australia. So it’s test of the “enemy release hypothesis” (leaving behind the herbivores and parasites) but with the addition of a “making new friends” hypothesis, i.e. gaining pollinators and other mutualists. That grant, plus a Visiting Fellowship to UNSW, is funding the trip.

In a post back in May I mentioned the Australian PhD researcher, Zoe Xirocostas, who is also working on this project.  Zoe surveyed plant populations in the UK, Spain, France, Austria and Estonia over the summer. She is now back and in the middle of surveying in NSW, Victoria and Tasmania.

As well as that project I want to spend time finalising my forthcoming book, collecting some data on Apocynaceae pollination ecology (of course!) and do some community-level surveys of wind/animal pollination to add to a global data set I am compiling.  Karin and I are also running a workshop at UNSW on “Writing for non-academic audiences” and I’m also giving a research seminar there and at Western Sydney University.  In addition we are visiting friends and family over Christmas and the New Year.  We’re packing a lot into a trip of two months!  And of course work at the University of Northampton never goes away – I have project students and PhD researchers to advise and there’ll be the usual weekly blizzard of emails to clear…

Having not been back to Australia since 1994 it will be interesting to see how it’s changed – a lot drier and smokier I imagine…  I’ll be updating the blog as the work progresses; over and out until we land in Sydney.

“Weighted” nestedness and “classical” nestedness analyses do not measure the same thing in species interaction networks

This post resulted from a question I posed on Twitter last week and hopefully summarises the issue as I see it and the results of the discussion with colleagues that followed.  Let me know if you disagree or if I have missed anything.


The use of network approaches to understanding how plants and their flower visitors interact has revolutionised the study of these and other mutualistic assemblages of species.  It’s a subject I’ve discussed on the blog before, highlighting some of the work we have published – for instance, see Plant-pollinator networks in the tropics: a new review just published and Local and regional specialization in plant–pollinator networks: a new study just published as two recent examples.

One of the recurring patterns that we see in mutualistic species networks (but not in antagonistic ones such as host-parasite and predator prey) is “nestedness”.  In a nested assemblage of species, generalists with lots of links to other species interact with other generalists and with specialists (those species which have few links to other species)Conversely, specialists tend only to link to generalists: specialist-specialist interactions are rare.  In nature, when we rank species in a network from most to least generalised, this sort of relationship looks like this:

South Africa nested

The rows are plants and the columns are pollinators, in this case from an assemblage of asclepiads and their pollinators we studied in South Africa.  A filled cell in the matrix indicates an interaction between that particular plant-pollinator combination.  It’s not perfectly nested by any means, but statistically this is not a random pattern and it comes out as nested when analysed.  There are a few ways of doing this but the most commonly used is the Nestedness metric based on Overlap and Decreasing Fill (NODF) developed by Almeida-Neto et al. (2008).

I first saw nestedness discussed in relation to plant-pollinator interactions in a presentation by Yoko Dupont of her PhD research at a SCAPE meeting in Sweden in 2001.  It was one of those “A-HA!” moments in science when the light bulb switches on and you realise that you are seeing an important new development which adds significant understanding to a field.  Yoko subsequently published her work as Structure of a plant–flower‐visitor network in the high‐altitude sub‐alpine desert of Tenerife, Canary Islands.

The nested pattern of interactions is conceptually derived from earlier work on island biogeography and species-area relationships and was initially developed to apply to interaction networks by Jordi Bascompte and colleagues in Spain and Denmark – see: The nested assembly of plant-animal mutualistic networks.

What was so exciting about this idea to me was that it provided a way to formally analyse what many of us had been observing and discussing for some time: that mutually specialised plant-pollinator interactions between species are rather rare, and that specialists tend to exploit generalists.  This makes perfect sense because specialist-specialist interactions may be more likely to go extinct, though why it does not also apply to host-parasite interactions is far from clear (and in fact the best known specialist-specialist interactions tend to derive from seed parasitism interactions such as fig-fig wasp and yucca-yucca moth relationships).

Fast forward 20 years and the plant-pollinator networks literature has exploded and our methods of analysis are much more sophisticated than they were in the late 1990s and early 2000s.  Every few months researchers are coming up with new ways in which to analyse these networks, mainly using the R environment for statistics and graphing.  Anyone entering the field would be forgiven for being bewildered as to which approaches to use: it’s bewildering enough for those of us who have been following it from the start!

One thing has been particularly bewildering me for a few years now, and that’s the introduction of “weighted” nestedness.  “Weighted” in this sense means that the abundance or interaction frequencies of the species in the network is taken into account in the analyses.  Visually it could look something like this if we code the cells in the network above to represent abundance or frequency (the darker the cell, the more abundant or frequent):

South Africa nested weighted

I’ve just mocked up the network above, it’s not the actual data.  But quite often networks look like this when we weight them: generalist interactions and/or species tend to be more frequent than specialist.  So far, so obvious.  But here’s the thing: networks that are statistically significantly nested when analysed by NODF tend to be not significantly nested when analysed by a new set of weighted metrics such as wNODF or WINE – see the documentation for the bipartite package for details.   And I don’t understand why.  Or rather I don’t understand why we should be using weights in an analysis of nestedness which is, at its heart, an analysis of presence-absence.  Species are either there or they are not, they are either interacting or they are not.  Their frequency or abundance is immaterial to whether a network is nested.  Indeed, assessing frequency of interactions in plant-pollinator networks is fraught with difficulties because (a) there are so many ways in which to do it; and (b) interactions between plants and pollinators in a community can vary HUGELY between years and across the geographical ranges of the species involved.

This should concern the interaction network community because recently I’ve had reviewers and co-authors saying things like: “don’t analyse for nestedness using NODF because wNODF/WINE is The Latest Thing, use that instead”.  But as far as I and the colleagues who commented on Twitter can tell, nestedness and weighted nestedness are different concepts and are not inter-changeable.  Indeed, many of us are struggling to really define exactly what weighted nestedness analyses are actually measuring.  I can define nestedness in simple terms as a verbal concept, without using the word “nested”, as you saw above.  I can’t do that with weighted nestedness, and I have yet to encounter anyone who can.

So the consensus from the Twitter discussion seems to be that:

  • for any study we should use only those analyses that are relevant to the questions we are asking rather than simply running every available analysis because there are lots to choose from.
  • weighted interaction networks that include abundance or frequency are not necessarily superior to binary presence-absence networks.  Again, it depends on the question being asked.
  • we should not treat weighted nestedness as an upgraded or superior version of classical nestedness.  If you are interested in nestedness, use a binary analysis like NODF.

My thanks to the colleagues who contributed to the Twitter discussion:  Nacho Bartomeus, Pedro Jordano, Pedro Luna, Marco Mello, Chris Moore, Timothée Poisot, and Kit Prendergast.  If you want to follow the Twitter discussion, start here:  https://twitter.com/JeffOllerton/status/1159377089319047168