How to be an ecologist #4

The British university system somehow manages to train ecologists despite two major impediments: most universities are in cites and all teach during the periods of the year that are least enticing for the budding field scientist.   Together, these factors work as two strong selective factors: getting thoroughly damp in a forest in Hampshire on a wet Sunday (because it is easier to timetable a whole day trip at the weekend), following a two hour coach trip, is a fine way of weeding out those with romantic notions of ecology gleaned from David Attenborough documentaries.

Then, of course, there is the residential field course, where students are immersed in an alien environment for an entire week (two, in some cases). These days, field trips seem to function as part of the marketing blurb in the prospectus, with departments vying with each other to offer the most exotic location. It makes as much sense to the customer (and that is what students are, let’s be honest) as a financial advisors offering a free pen to anyone who signs up to a pension plan.   Back then, we were taken, by boat, to Blakeney Point in Norfolk, and dumped outside the wooden hut that served as University College, London’s field station. We camped amongst the sand dunes and spent the days learning about the saltmarsh and sand dune plants under the tutelage of Dickie Clymo.

I still contend that you can learn more in a week about plant ecology on a British salt marsh or sand dune than in twice that time in a more exotic habitat.   Sand dunes and salt marshes have the additional benefit of having only a limited number of species, which means that we were able to focus on why they grew where they did rather than having to memorise long lists of names.   But then I do not have to recruit students for a degree course.

saltmarsh_vegetation_at_Bla

Left: saltmarsh vegetation at Blakeney Point, Norfolk, October 2011; right: close up of Suaeda maritima (Annual Sea Bite) from Blakeney Point.

I also learned a second very important lesson about ecology: that week among the sand dunes generated enough data to keep our ecology class busy through the winter months, as we analysed the data in all sorts of ways.   I learned multivariate statistics – ordination and classification – the slow way, crunching the numbers by hand.   The process worked, I think, because we could relate the graphs we produced to the communities that we had seen just a few months earlier.   I found Dickie Clymo’s way of teaching ecology sufficiently inspiring that I opted for a plant ecology-based project in my final year, and Dickie set me to work on his favourite type of habitat (the peat bog) and plant (Sphagnum moss).

I dug my dissertation out of the loft to see how it had stood the test of time as I was thinking about the post and memories came rushing back. My aim was to look at how the density of Sphagnum plants in a peat bog affected their properties.   I had read parts of John Harper’s book Population Biology of Plants during Dickie’s ecology course and was interested in how organisms competed with one another.   Bogs are seemingly prosaic habitats but, like the salt marshes where we had honed our ecological skills, they were excellent testing grounds for new ideas.

Thursley_Common_1983

Sampling Sphagnum at Thursley Common, Surrey, early in 1983.

I made two visits to lowland bogs in southern England, Cranesmoor in Hampshire and Thursley Common in Surrey, pushed a metal quadrat with 3 cm sides into the top of the bog at various locations, and removed 1 dm2 squares of Sphagnum to take back to the laboratory. There, I counted the number of shoots and measured the length and mass of the green parts of the shoots. It was slow, painstaking work, which I slotted around my other lectures during my final year at Westfield, sitting in one corner of a research laboratory that Dickie’s PhD student shared with Brenda Thake’s students.   I also tried to look at the amount of chlorophyll in Sphagnum plants, and have a scar from pushing a pipette bulb onto a pipette with so much force that the pipette snapped and drove into my finger. This happened on a Sunday afternoon, when I was working in the laboratory on my own.   Back in those unenlightened days, I can’t even remember filling in an accident form.

Sphagnum_density_fig1

The effect of density on shoot mass in different species of Sphagnum from bogs in southern England. Pearson correlation coefficient, r = 0. 75, P < 0.001. From my undergraduate dissertation.

The first graph that I have included makes a point that may be rather obvious to anyone who has grown vegetables – that the greater the density of shoots, the smaller each shoot tends to be.   They are competing with each other for resources and, the more plants that there are, the fewer resources each shoot can acquire.   Having made that point, you’ll see that species that tend to be found on the hummocks in peat bogs – such as S. capillifolium – tend to be smaller than those found in bog pools – such as S. subsecundum and S. cuspidatum.   The crowding may actually favour the former as they rely on capillary action to draw up the water that they need from the bog.

However, each shoot of Sphagnum is not really an independent “plant”, simply one of many genetically identical clones (called “ramets”) of a much larger organism.   The individual, in the sense that you and I are unique beings with a distinct genetic identity (a “genet”), is hard to distinguish from it’s neighbours; however, we can infer the response of the individual to density by looking at the frequency with which branches fork (leading to an increase in the size of the genet.   Once again, there was a linear relationship to density, with the greatest frequency of forks observed at low densities, suggesting that density was influencing the size of genets, as well as ramets. Of particular interest to me was that the slope of the relationship (ignoring the two pool species) was -1.42, which is close to -1.5, the theoretical relationship between density and the size of genets proposed in a 1963 paper by Japanese workers (“the -3/2 self thinning rule” which, I confess, I wrote in my lecture notes as the “three tooths law”, as if it were some arcane Japanese philosophical notion). It suggests that an element of “survival of the fittest” was working within Sphagnum populations, in ways that it was not easy to perceive.

Sphagnum_density_fig2

The effect of density on the probability of a shoot of Sphagnum forking. The two points in the lower left hand corner (circled) are both pool species. Pearson correlation coefficient, r = 0.551; P < 0.05 (ignoring these two points). From my undergraduate dissertation.

Work on my dissertation took me perilously close to the start of my final examinations and I remember when Brenda Thake, phycology lecturer and unofficial mentor, took me aside and told me bluntly to finish writing and get stuck into some serious revision.   On reflection, I had reached the stage when data that has taken a long time to acquire (long enough, indeed, for you to question the validity of your original hypotheses) suddenly comes together. After all that time, there is a delirious sense of intoxication as you get stuck into the analyses and see patterns emerge.   It was my first taste of research as a vocation rather than as just another job, and it confirmed my desire to continue with my studies.

But that’s a story for another day.

Reference

Clymo, R.S. & Hayward, P.M. (1982).  The Ecology of Sphagnum.  In: Bryophyte Ecology (edited by A.J.E. Smith).  Chapman & Hall, London.

Harper, J.M. (1977). Population Biology of Plants. Academic Press, London.

Yoda, K., Kira, T., Ogawa, H. & Hozumi, K. (1963). Self thinning in overcrowded pure stands under cultivated and natural conditions. Journal of the Institute of Polytechnics, Osaka City University, Series D 14: 107-129.

Advertisements

2 thoughts on “How to be an ecologist #4

  1. Pingback: How to make an ecologist #5 – microscopesandmonsters

  2. Pingback: How to make an ecosystem – microscopesandmonsters

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s