I am delighted to report that Dr Encarnacion Montoya Romo (currently of the Botanical Institute of Barcelona) has been awarded a NERC Fellowship to join the PCRG. The project is entitled “Evaluation of tropical forests sensitivity to past climate change” (FORSENS) and will examine environmental change at four study sites from different regions of the Neotropics: 1) Khomer Kotcha (Bolivia; 17oS, 4100 m above sea level [asl]) [1-3], 2) Consuelo (Peru, 13oS; 1400 m asl) [4-5], 3) Banos (Ecuador; 0oS, 4000 m asl), and 4) a new lowland site from Columbia/Ecuador to be collected during field work during the project.
The aim of the project is to explore the spatial and temporal consitance of tropical vegetation response to aridity (mid-Holocene dry period) and warming (last deglaciation). The project will use fossil pollen, chironomids, charcoal, non pollen palynomorphs and organic biomarkersto build up a comprehnsive picture of environmental change. The diversity of the project means we have a number of exciting partners, including: Steve Brooks (Natural History Museum), Prof. Mark Bush (Florida Tech), Prof. Valenti Rull (Botanical Institute of Barcelona) and the Dr. Pauline Gulliver (NERC radicarbon facility).
The fellowship will commence in October 2012. Further information will appear on is blog and group website soon.
I have been engaged with two major activities during June: 1) submission of a research proposal to NERC, and 2) excitement of my first online teaching module going live to students, Cyprus activity, within Practical science: Earth and environment module (SXG288). Other members of the group have been writing up methods chapters (Natalie), number crunching and submitting abstract to the International Paleolimnology Symposium (Lottie), and submitting first year probation reports (Hayley and Frazer).
Last month I attended the Numerical Analysis of Biological and Environmental Data course at University College London (UCL) in order to decipher which techniques of multivariate data analysis would be useful to apply to my data from Lake Bosumtwi (Ghana). The course was led by Dr Gavin Simpson (UCL) and Prof. John Birks (University of Bergen), both of whom are well experienced in quantitative palaeoecology.
The course provided an introduction to the methods, guidance as to when to use the techniques and then outlined the assumptions, limitations and strengths of the various methods. The need to fully understand the techniques applied before attempting to critically evaluate the results was also strongly emphasised.
The course consisted of lectures covering measures of dispersion, cluster analysis, dendrograms, regression analysis, tree models, gradient analysis, transfer functions, time series and hypothesis testing. Afternoon practical computer classes involved using R, C2 and CANOCO to implement the various techniques covered in the lectures.
Overall the course was a great introduction to statistical analysis which I would certainly recommend for anybody working with complex and noisy datasets. In the next few days I will be using my newly learnt R skills to run indirect gradient analysis such as PCA, CA, DCA and NMDSCAL to search for environmental gradients within my data.
Numerical Analysis of Biological and Environmental Data training couse is an annual event and was held at UCL, on 14-25th May 2012. For more information about the course see Gavin’s website or read his blog From the bottom of the heap.
Time seemed to escape me in April so I have a lot of research group action to report in this post! Here are some highlights…
At The Open University (OU) the research students have all been busy (of course): Natalie presented her 3rd year talk at the CEPSAR student conference and attended a meeting in Durham, Lottie spent two weeks at University College London (Environmental Change Research Centre) learning to become a statistics guru studying the “Numerical Analysis of Biological and Environmental Data” course, while Hayley and Frazer have been writing up their first year probation reports ahead of their mini-vivas next month. Over in Florida Bryan submitted his first PhD paper and has headed off on field work in Peru; and most significantly… I am very pleased to report that Nikki successfully defended her PhD thesis! Congratulations Nikki!
Thinking of PhD I was also pleased to have the opportunity to welcome my PhD supervisor, Frank Mayle, to The OU to give a CEPSAR seminar last week. It was great to be able to show off the labs to Frank at last having promised to invite him down when I arrived at The OU in 2005! He gave a very interesting talk on new archaeological findings from beneath the rain-forest in the Amazon Basin.
Away from The OU a couple of weeks ago I was down at Charles Darwin House for the British Ecological Society meetings committee meeting! We were working on the program for the annual meeting in Birmingham during December this year and it is shaping up to be a very exciting event; keep up to date by following the BES on twitter (@BritishEcolSoc).
CHIRONOMIDAE AS A PALAEO-ECOLOGICAL TOOL
Chironomidae is a family of two-winged flies more commonly referred to as non biting midges. This diverse group of insects have been known for a long time to be sensitive environmental indicators. Early research in the field showed that the trophic status of lakes could be classified according to the characteristic chironomid assemblages found within them (Thienemann, 1922). Furthermore the head capsules of the larvae are well preserved within the sedimentary record. As a result palaeolimnological researchers became increasingly interested in the potential for using Chironomids to track the trophic development of a lake through time by examining the changing assemblages within the accumulated sediments. With geographically close lakes displaying significantly different midge faunas the potential for the insects being used as climatic indicators was dismissed and the following hypothesis became established: Chironomid assemblage composition reflects in-lake variables, e.g. lake depth, pH, dissolved oxygen, trophic status and substrate. However work by Walker and Matthews (1989) demonstrated that temperature was by far the most significant variable in controlling the broad scale distribution and abundance of midge fauna.
Walker and Matthews realised the potential for the non biting midge to be used as a palaeoclimatic indicator from two initial observations. Firstly within the fossil records, as climate began warming following the deglaciation of the northern hemisphere, the relative abundance of taxa associated with cold oligotrophic lakes (Heterotrissocladius) abruptly declined. Secondly they noticed the best analogues for late glacial assemblages were found in modern day arctic and alpine settings. Overall Walker and Matthews concluded that the northern limit of temperate taxon was controlled by cold summer air and/or water temperatures. The southern limit of Arctic species was instead driven by cold oxygenated refugia in the profundal zone of deep, temperate lakes. These temperatures were significant with respect to the insect’s life cycles as many species require critical temperature thresholds to complete pupation and emergence stages.
Since the pioneering work of Walker and Matthews (1989) and others the debate linking Chironomids to temperature has raged. Debate has centred upon what controls chironomid distribution and how suitable, if at all, the insects are in the context of palaeoecological studies. Recently Velle et al. (2010) discussed some key factors which must be considered when working on chironomid based temperature resonstructions.
Below I present some of the debate around the midge-environment-temperature debate; focusing on both midge distribution and identification and the potential of this proxy as a indicator of past environmental and climatic change.
HOW DO WE UNDERSTANT PAST VEGETATION CHANGE?
Our understating of vegetation in the past, and how it has changed through time, comes mainly from the examination of macrofossils (e.g. wood and leaves) and microfossils (e.g. pollen and spores) found in the sedimentary record. The potential for microscopic fossils to provide an insight into past vegetation change on a landscape scale was pioneered by von Post (Von Post, 1916, reprinted 1967) and has been subsequently used to understand changes in regional floras (Godwin, 1956), and address conservation issues (Willis et al., 2007). Analysis of fossil pollen and spores (palynology) is now widely used on late Quaternary timescales to answer ecological questions linking vegetation and wider environmental/climatic change; these include:
Palynological analysis relies on obtaining a sub-sample of the pollen contained within the sediment at a specific depth (time) which allows the vegetation at that time to be reconstructed. This sub-sample is known as a pollen count. To build up a picture of vegetation change through time it is necessary to generate a sequence of pollen counts. The size of the sub-sample (pollen count) required from any particular depth (time period) is dependent on the nature of the vegetation association being investigated and the ecological question being addressed . For example, the amount of pollen analysed to determine if the vegetation was predominantly wooded or grassland is different to that required to provide information on the biological diversity within the vegetation assemblage.
Discussed below are some of the conventions related to choosing an appropriate pollen count size within palynology, with particular reference to the challenges of dealing with diverse tropical floras.