Tuesday, 13 June 2017

Square-bashing in Scotland - some basic statistics

Between 31 May and 10 June I made my way through Scotland, staying at four localities: St John's Town of Dalry, Moffat, Tarbet (Loch Lomond) and Kingussie. Conditions were far from ideal, with several spells of wet weather and most of the time there was a risk of rain. This severely attenuated what I had intended, especially my wish to do some serious recording at Rowan in the Spey Valley. It meant that I spent far more time sweeping and relatively little time watching Rowan flowers. The records reflected this, with Bacchines and Chrysogastrines dominating the catch Table 1).
Table 1. Composition of the records at Tribe level.

The dominant species in most samples were the genera Melanostoma, Platycheirus and Sphegina, which is not entirely surprising bearing in mind that sweeping tends to yield far more of these genera than basic visual searches. Generating a decent list does, however, involve retaining quite large numbers of specimens because there is always a dominant species and a tail of species that are far scarcer. The lists tell their own story, with good representation of species in Platycheirus, including many of those that one sees relatively infrequently further south (Table 2). One that I would single out is P. podagratus, which I think is a relatively early species and was probably on the wane when I arrived. My records mainly comprise females, so I suspect males were substantially over.

What is especially noticeable from the records is the relative lack of Syrphini, which are far more likely to be recorded as flower visitors and by active searching. Similarly, the Cheilosini were relatively poorly represented; I think for similar reasons.

Table 2. Species list for the trip, with numbers of records (record = occurrence of individual genders, so the actual numbers will be lower)
The final tally of coverage was relatively good, with 49 10km squares visited (Figure 1). Had conditions been better I would have expected the coverage to have been closer to 60 10km squares and a lot more records, but I made up for the lack of hoverflies by recording other taxa. There are a lot of fungus gnats and craneflies for identification by Peter Chandler and Alan Stubbs, and I have lots of sawflies, a few beetles and a scattering of other Diptera families to deal with. So, overall, the trip should have been reasonably productive. I will write more on other aspects of the trip in due course.

Figure 1. Coverage at 10km resolution

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