Monthly Archives: January 2014

Ménage à trois mutualism

Lymington 2007 057

Relationships involving a “household of three” hold a fascination that is part prurient and part wonderment: prurient for perhaps obvious reasons, and wonderment as it’s sometimes hard enough to make a ménage à deux work! Historically this domestic arrangement has been the lifestyle of choice of a surprisingly large and diverse set of influential thinkers and creative individuals, including Aldous Huxley, Lord Nelson, Carl Jung, Erwin Schrödinger, and Hattie Jacques.  Indeed, one of my favourite musicians, David Crosby, wrote a song about such relationships (Triad) which got him kicked out of The Byrds.

In nature, ménage à trois are occasionally encountered and may be more common than we think, and have been on my mind because this week I’ve been talking about mutualistic relationships with my first year undergraduates.  Mutualisms are interactions between species in which both benefit, as opposed to exploitative relationships such as predation or parasitism in which one of the partners is at a disadvantage (being eaten is a great disadvantage….)  Mutualistic interactions are common and important, and include many (but not all) plant-pollinator interactions, seed dispersal by birds and other animals, mycorrhizal relationships between plants and fungi, and many more.  As well as studying plant-pollinator interactions, I’ve a long-standing interest in the full breadth of these examples of “biological barter“, in all their varied forms.

In most cases mutualistic relationships involve pairs of species (for example a plant and a pollinator) although these species pairs are embedded within a larger network of interactions: that plant may have many pollinators, and those pollinators may service other plants.  In this sense it requires just two partners to make the interaction work – a “household of two”.  More rarely, research on the biodiversity of species interactions throws up examples of “households” involving three species, and a fascinating case has recently been worked out and published by Jonathan Pauli and colleagues.  This involves three-toed sloths and their relationship with the algae and moths that colonise the sloth’s fur – you can read the abstract here.  In summary, the algae benefit from nutrients provided by the moths living in the fur; the sloths eat the algae to supplement a restricted diet of leaves; the moths benefit from the sloths transporting them to defecation sites where they lay their eggs, then recolonise the sloths.  This slothy ménage à trois is a wonderful instance of interdependency within nature.

The other case of a three-part mutualism with which I’m familiar is that between anemonefish, and sea anemones and the algae which are housed in their tentacles.  The fish and the anemones provide mutual defence of one another, whilst the algae photosynthesise and provide carbohydrates to the anemone, and benefit from the nitrogenous waste produced by the fish.  It’s a system that I’ve done a little work on with marine biologist colleagues, specifically the broad scale biogeography of the interaction and its local assemblage structure, but we’ve not studied the whole three-part system. 

What other three-part examples are there in nature?  I’d be very interested to hear about any of which you’re aware.

It begs a question as to whether three is an upper limit to the number of species that can engage in such relationships?  Are there any four- or five-part mutualisms?  Or are these too unstable over evolutionary time, because if one species goes extinct it could cause the extinction of other species?  Interesting questions about fascinating interactions!

Ordinary by Choice

August 2009 - including Gardeners World shoot 029

Until the system changed a few years ago it was a requirement of all course leaders at the University of Northampton to attend Award Boards at which the students graduating that year were named and their degree classification confirmed.  It was not popular with academics, as you can imagine, as we spent half a day waiting for the turn of “our” course.  Typically we would take manuscripts to revise or crosswords to complete, or a good book to read, until such time as it came to our own students.  As each student’s name was read aloud, their degree classification was confirmed:  “First Class Honours”, “Two-One” (Upper Second Class Honours), “Third” (Third Class Honours), and so forth.

One category was rarely used:  “Ordinary by Choice”, meaning that the student had not completed a final year dissertation and had opted to take an Ordinary, as opposed to Honours, degree.  It is a phrase that I was always struck by: except for a (perfectly respectable) Higher Education qualification, would anyone elect to be “Ordinary by Choice”?  Do we want that for our lives, our country, our society,  or even our environment: Ordinary by Choice?

The phrase came to mind last week when I heard about an interview with Owen Paterson, Secretary of State for Environment, Food and Rural Affairs in the current British Government.  Paterson, who coincidently studied at the precursor to the British School of Leather Technology here at Northampton, said that in the future it might be perfectly acceptable to build on ancient woodland if the destruction of that site was offset by planting trees elsewhere.  A spokesperson for his department later said that it was “highly unlikely” that such development would ever occur on ancient woodland, but that’s not the same as “never”.

In fact such destruction of ancient woodlands is currently being proposed by the development of the High Speed Rail 2 (HS2) line from London to points north.  An analysis by the Wildlife Trusts of the currently proposed HS2 route shows that it will pass through “10 Sites of Special Scientific Interest (SSSIs), more than 50 ancient woodlands and numerous local wildlife sites”.  Important wildlife sites are perhaps not as safe as government would have us believe.

From the outset let me say that in my opinion this notion of “biodiversity offsetting“, in which one can apparently trade like-for-like in the destruction and recreation of natural habitats, putting back or even enhancing the biodiversity of a region, is pure fantasy dreamt up by government.  It can’t be done.  It’s not possible.  The reason?  There are no complete inventories of the biodiversity of any patch of planet earth.  None.  Not even of a few square metres of arable grassland in rural England, a simple habitat in comparison to the fantastically complex biodiversity of an ancient woodland.  Such All-Taxa Biodiversity Inventories (ATBIs) have been proposed in the past, but never completed.

Now I am using a strict definition of biodiversity to include all of the diversity of life within an area, including not only plants, birds, mammals, and large insects, but also the many smaller insects and other invertebrates, algae, protists, fungi, and bacteria.  But that’s not what the proponents of “biodiversity offsetting” such as Owen Paterson have in mind when they champion the system.  What they really mean is “species offsetting”: for example cutting down an oak forest and replacing it with young oak trees planted some distance way; or destroying a wetland used by over-wintering birds and creating an artificial wetland at another locality.  In both cases the species in question will persist: oaks will grow and birds will over-winter.  The assumption is that the other elements of biodiversity, the neglected micr0-invertebrates, bacteria, lichens, fungi, and so on, will also return.  It may take some time, perhaps hundreds of years, but (goes the logic) they will eventually come back and the habitat will contain the richness of species that there was previously.

This may happen, but not for all species, particularly naturally rare organisms with small populations and low dispersal abilities.  The fact that (as I’ve noted) we have no complete inventories of biodiversity for anywhere on the planet means that we currently cannot be certain about how “biodiversity”, as opposed to “some of the larger and obvious elements of biodiversity”, can spread and re-establish.  In contrast, all of the available evidence suggests that the historical continuity of a site is vital to its current biodiversity.  Let me give you an example, in fact from a data set that I’ve never published.

About the time I arrived in Northampton (in 1995) I started to develop a more serious interest in fungi – moulds, mushrooms, and toadstools.  Together with colleagues in the department and some of my students I began to systematically identify the fungi in a long, narrow patch of woodland (the “Shelter Belt”) on Park Campus.  Early on I set out a series of 1m x 1m quadrats and every week for two months I recorded which fungi appeared.  It was a short survey but very revealing because it was clear that there were differences in the diversity of fungi in different parts of the Shelter Belt, and that some areas had much richer diversity than others, even over a distance of a few tens of metres.

In fact the western side of the Shelter Belt contained almost twice as many species of fungi as the eastern side.  In addition there were few species on the eastern side that were unique to that area: most species were also found in the western portion.  This is despite the fact that the woodland appeared very homogenous: a linear strip dominated mainly by the non-native Black Pine (Pinus nigra) with an under-storey of common small trees such as Holly (Ilex aquifolium), Elder (Sambucus nigra) and Hawthorn (Crataegus monogyna).

A likely reason for this difference was revealed when we studied some old maps of the area; a sixteenth century map showed that there was a hedgerow on the site of the western part of the Shelter Belt from at least Tudor times, and probably much earlier.  This hedgerow may have been planted as a boundary for livestock, or may have been a remnant of an even older patch of woodland that was felled and managed to partition agricultural fields.  The presence of plants which are known ancient woodland indicator species, such as Wood Anemone (Anemone nemorosa), Bluebell (Hyacinthoides non-scripta) and Dog’s Mercury (Mercurialis perennis) was further evidence.

So an ancient hedgerow, now erased and replaced by later planting that was at least 50 years old (it appears on Google Earth historical imagery for 1945), was continuing to influence the biodiversity of a site long after it was gone.  But that influence was subtle and involved a neglected element of wildlife that is nonetheless vital to the natural world: fungi, which act as decomposers, consumers and recyclers, and without which a woodland could not function.

The definition of “ancient woodland” in England and Wales is an area of woodland that existed prior to 1600 and the Shelter Belt example shows why this definition is important: the history of a site has a huge impact on its biodiversity.  Simply planting a new woodland of young trees will not replace what is lost by the destruction of a site with historical continuity of habitat which is supporting slow-spreading species.

Government and the public have a choice: we can sanction the destruction of truly biodiverse sites such as ancient woodland and replace them with ordinary ones, such as new planting of trees on farmland.  Is that what we want, an environment in Britain that is Ordinary by Choice?


Two turtle doves……?

Mainz 2009 007

On the Second Day of Christmas my true love sent to me
Two Turtle Doves
and a Partridge in a Pear Tree.

So goes part of The Twelve Days of Christmas, a song that can be dated back to the late 18th century, and which celebrates the period between Christmas Day and the 5th January.  The chances are that few people under the age of 50 will have seen the culturally iconic turtle dove in the wild in Britain as it’s a species which has reduced in numbers by a spectacular 93% across Britain since the 1970s, as this graph shows.  Not only that, but the British Trust for Ornithology suggests that the turtle dove is “one of the most strongly declining bird species across Europe since 1980”.  Clearly this is an issue not just for the U.K. and organisations such as the RSPB have responded with schemes focused on turtle dove conservation.

If you’ve been following the various news items about nature and conservation over the festive period you’d be forgiven for being a little confused by the mixed messages.  On the one hand the turtle dove and other farmland species, as well as wetland birds, were shown to be suffering long term declines in the State of the U.K.’s Birds report for 2013.  But then we have the National Trust telling us that 2013 was the best year for wildlife for a long while, with nature thriving in the long, hot summer.  Which of these is true?  Both of them are, of course, it’s just that the scales at which they are assessing their results are very different.  Whilst analyses of single years are important and can provide some grounds for conservation optimism, it’s the long term trends that really matter.  And for many species these trends are not looking good.

With this in mind it was hoped that the budget announcement by the Department for Environment, Food and Rural Affairs (Defra) might contain some good news for Christmas, but it was not to be: overall, there will be less money available for agri-environmental schemes on UK farms in the foreseeable future, a situation that the RSPB states “falls short of what nature needs for recovery” and the Wildlife Trusts describes as “a missed opportunity to boost investment in wildlife-friendly and progressive farming“.  As always, Mark Avery’s blog had some forceful opinions on the subject and is a recommended read on this topic.

On the Twelfth Day of Christmas my true love sent to me
Twelve drummers drumming…..

…hopefully drumming up government support for some real action in 2014, rather than fine words and greenwash, to begin to reverse the loss of our native biodiversity.  Happy New Year everyone.