Sunday, 20 April 2014

What flies do photographers focus on?

As interest grows in the possible uses of web-based recording, it crossed my mind that it would be worth looking at the data for flies. Until last year I did not maintain a log of hoverflies that could not be identified, so the dataset prior to mid-summer 2013 is only partial. I therefore selected the data for 2014 only, working on the principle that these data would offer a reasonably representative example of the situation between January and April. Obviously there will be much greater scope for evaluation at the end of the year, especially as there will be lots more species recorded during the summer.

Nevertheless, the data paint an interesting picture. They comprise all photographs where reliable locality data can be attributed. The only exception is that I do not extract records of tachinidae from iSpot because I know that Matt Smith (Tachinidae Recording Scheme) does this. However, I suspect this will make relatively little difference as the numbers of tachinids posted thus far have been quite small.

The graph (Figure 1) tells a facinating story. Firstly, it is clear that hoverflies make up the vast bulk of records. This year, the numbers are perhaps skewed by the development of the Facebook page (an additional 263 records over and above data from other sources), so I have excluded these records from the graph. The other families that attract attention are the bee-flies (Bombylius major dominates but there have been a few B. discolor), the Calliphoridae (bluebottles etc), what I will call 'Muscoidea' because this tends to be a dump for bristly jobs that I cannot readily place to family, and the Scathophagidae (dominated by Scathophaga stercoraria but with several Norellia spinipes). Other families figure quite lightly at the moment but I expect the Bibionidae to surge forward over the coming weeks.

Figure 1. Numbers of photographs of Diptera families logged for 2014 (1 January to 20 April 2014).
Why is there such a bias in the numbers? Well, clearly my focussing on hoverflies is a factor. I do not chase up shots of other flies that lack locality data, unless they are identifiable. So, there would otherwise be a bigger dataset. But, in reality, the Flickr groups and sets are not heavily dominated by non-Syrphid flies. Hoverflies are genuinely a major component of what is noticed and photographed. There are a few surprises, however; not least the frequency with which moth flies (Psychodidae) are depicted. I guess they are obliging and don't generally fly at the first provocation?

Now, having recognised and identified possible bias in the dataset, I wonder if there are other factors at work? I wonder whether there is an element of inbuilt bias because photographers start to know the flies that they or others are most able to put names to? Clearly this is not wholly the case because lots of shots of bluebottles and muscids are posted. Perhaps, therefore, the key is the frequency with which particular subject-matter is encountered, and whether it is willing to act as a model?

Is the picture that is emerging for Diptera the same for other Orders? Whilst I browse the web I get an impession that a similar sub-sample might be seen amongst the bees and wasps, amongst beetles and spiders and true bugs. I don't know whether higher levels of identification are possible amonst these groups? Somehow I doubt it? But, can it be quantified, and are there other recording scheme organisers who keep a similar log to the one I maintain. If such logs do not exist, perhaps there is a need to develop a co-ordinated approach to data extraction from the web. I think there are definite benefits to be had from internet recording, but there are also drawbacks. The question is, are there similar drawbacks for each insect Order, or are the limitations confined to certain Orders?

These issues are worth exploring further because there appears to be a dichotomy of views amongst recorders. Some are alert to the potential of internet recording, whilst others dismiss photography as a way of getting records. Clearly, those who dismiss photography have a good reson to be sceptical but it is well worth developing a much clearer picture of what can and cannot be done. Malcolm Smart and I have looked at the Asilidae (Malcolm is currently working though last year's photos). In an analysis of the Asilidae records I developed to 2012, he managed to identify the vast majority of shots (94%), generating at least one record of 20 species (74% of the family); but just six species formed 68% of the data.

I hope to develop further analyses over time, so that we have at least a basic understanding of the flies that are recorded by photography. It might take a little while, however!

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