Drought & the Diptera Crash

In the most recent Bulletin of Dipterists Forum (No 86: page 18), Alan Stubbs writes on the impacts of drought upon Diptera. He also highlights the problem of developing long-term datasets that are compiled in a consistent manner. He draws attention to his own long-term garden monitoring effort and that of Jenny Own in Leicester and reflects on the absence of any other similar efforts. His concluding comments focus on Recording Schemes and suggest that they should be developing ‘practical ideas on how some aspects of monitoring might be achieved’.

I’m afraid my immediate response is that we have been trying to achieve a long-term approach for several years. We tried to get a garden monitoring scheme up and running some years ago, but it proved impossible to get enough traction to make the results meaningful. More recently, we launched our ‘carrot flower challenge’ that generated a certain amount of interest but also highlighted the numerous problems of getting something practical to work. My carrots were eaten by slugs and I think several others met the same sorry end! Back to the drawing board! The other big problem that these efforts highlighted was the need for a much bigger pool of 'shakers and movers' who would act as motivators and administrators. Sadly, I am woefully lacking in any ability to run a multitude of initiatives!

So, are there any other practical ideas? I don’t have any! Formal monitoring programmes need a big pool of interested and capable people. Amongst Diptera schemes, I think the only one where there might be enough recorders is the HRS. Even there, we are still relatively skills light, with a very small nucleus of experienced specialists. We are, however, in the fortunate position of having a growing nucleus of active recorders.

I think that we therefore need to think about this in a different way. There are quite a few members who regularly record from their garden or favoured walk. The current data run is relatively short, but it will get stronger over time. To pick up any sort of trend, one needs a data run of at least 5 years and a run of ten years or more is needed to generate anything meaningful. The sooner we have a big pool of people regularly recording from a favoured site, the greater the likelihood of having a reliable dataset to test theories in new situations. Let’s face it, the drought and heatwave of 2018 will not be the last such event; indeed, we must expect more in the not too distant future.

In the meantime, we do have a well-tested system for using opportunistic data to look at trends using occupancy models. These models are still evolving, and we are starting to have to tackle the problem of changing recorder methods having an impact on trends. I have written on this subject in the past (Data requirements for occupancy modelling – 23 May 2018). My feeling is that we have got to work with modelling teams to refine existing occupancy models and to develop new ones that take account of the range of species that can be tackled by a wider pool of enthusiasts. Beyond this, we do need to start to look quite carefully at existing data to try to understand the events that they portray.

I think we probably have enough data to start to interpret the effects of the 2018 heatwave and drought, but the big issue is context and whether any interpretation can rule out other compounding factors. There will inevitably be a variety of signals within the data, some of which will complicate our interpretations. Trying to make sense of these signals is one of the impending challenges.