Saturday, 24 December 2016

An exercise in parataxonomy

Earlier this month, I discussed a new paradigm in parataxonomy. In this post I describe some of the data developed by John Bridges (NE Wildlife) who has combined his amazing photographic skills with equal dedication in trying to make sure that the subjects captured as photographs are correctly identified. John's approach is one that might be of interest to other photographers who want to build up a more complete picture of the hoverflies that inhabit their favoured wildlife site(s).

John's technique is to settle at a chosen location and to wait for the subject matter to come to him. It can be extremely successful, as John has shown that there is a constant turnover of flies at suitable lures. His daily species lists are remarkably close to the level of coverage I would expect to achieve using net and pooter.

In addition to photographing everything that attends the chosen lure (a flower or possibly sugar-sprayed leaves), John captures a selection of specimens and retains them for photo-stacking at home. Each specimen is logged against the number of the photograph that recorded it. In this way, it has been possible to develop a quite comprehensive set of photographs with a firm identification of the corresponding specimen.

Once the specimen has been run through the keys, it is bagged up and retained for me to check later in the year. I have just completed this year's sample and thought it worth sharing with a wider audience because it is highly instructive of what can be achieved. His species-list for the year is just shy of 100 species, which is impressive when you bear in mind that north-east England is relatively species-poor and that John records from quite a restricted range of habitats. The list also contains a number of noteworthy species, including one of fewer than 20 confirmed records of Eristalis similis and one of Platycheirus aurolateralis, which is rarely seen and is extremely difficult to separate from the commoner P. splendidus. The list of species represented in the collected sample is represented in Table 1.

Table 1. Species represented in samples retained after photographing.

In addition to generating reliable records, John is helping to build up a valuable portfolio of live animal photographs that should help taxonomists better understand how to describe live animals rather than using specimens. This may, in the longer-term, help to improve our ability to provide reliable diagnoses from photographs.

Storing specimens

John's system involves labelled polythene bags that take up relatively little space and can be stored until the autumn when they are sent to me for verification (figures 1 & 2).

Figure 1. Samples awaiting identification

Figure 2. Sample checking in progress

In theory, it is possible to identify some of the specimens through the bag, but in practice I find it easier to remove them from the bag. I dispose of the majority of specimens on the compost heap, so I remove all from their bags anyway. A few are retained where they are important vouchers - they will find their way into my storage system. Others are retained to become part of the teaching pack that Stuart and I use in training courses.

This system has obvious advantages in providing a clear way of retaining specimens without having to pin them and then label them. There are drawbacks, however. The main problem is mould and decomposition. Last year, John stored the bags in the freezer, which meant that once defrosted they were still relatively fresh and could be pinned. Unfortunately, a small proportion went mouldy for some reason. This year, the specimens were simply stored at room temperature. Again, mould was a problem in about 10% of cases. The problem is more acute where an additional (un-photographed) sample is retained in the same bag. More condensation develops and mould is therefore a problem, as is specimen decomposition. In almost all cases I was able to verify the determinations made by John, but it was more tricky in some cases.

One answer would be to place specimens in the bags and leave them unsealed for a few days until the specimens have dried out. If left for 24 hours in this state, I think there will be lower risk. The system will hopefully be refined further in 2017.

Working through specimens stored in this manner is a little more time-consuming than working from pinned specimens, but it is a more practical way of working with recorders who don't have the facilities to pin and store specimens.

1 comment:

  1. I store specimens in glassine envelopes (philatelic suppliers sell them), inside a small sealable plastic box which is placed in a freezer. I guess small paper envelopes would be just as good (and cheaper). The key thing is that this reduces the capture of moisture that you get in a sealed plastic envelope. I have not had any issues with mould so far.