Thursday, 17 April 2014

Changes in recorder effort

The advent of digital photography and of web-based data capture techniques might suggest that biological recording is entering a new and vibrant phase. I'm sure it is, if one simply looks at the numbers of records that find their way onto databases. The big challenge is to establish whether these data actually reflect an increase in recording or a change in the ways in which plants and animals are recorded?

My interest in this stems from five years trawling through photographs on a wide variety of websites. I check between thirty and fifty sites each day, and during the summer months add between fifty and one hundred new records. I've posted some of the initial results in previous reports. My suspicion is that there will be considerable differences in the nature of recording, depending upon the ease with which animals and plants are both found and identified.

My instincts say that for those species that are easy to record there has been an increase in records. In the case of groups like macro-moths ,where moth traps have gained huge popularity, the volume of records may well have increased sharply. It would be interesting to see precisely what has happened. In the case of macro moths, perhaps there is an increasingly robust dataset? Moths are pretty docile and allow themselves to be photographed. Moreover, I suspect most can be identified from photos (I may well be wrong for a few genera).

Moving on to taxa where there is a need for specialist fieldcraft, and collecting specimens for microscopic identification, I suspect that what we are seeing is a shift in the robustness of the data. This was well demonstrated by Matt Smith and Chris Raper in their presentation of the Tachinid Recording Scheme at the last Dipterists Forum AGM. Chris and Matt showed that the data set was starting to change in composition as more photographic records were acquired. The most abundant species now include several that would be far less dominant if the data were strictly from what I would describe as taxonomist sources (i.e. people who actually study tachinids in a meaningful way).

The Hoverfly Recording Scheme has previously shown how the records of  more difficult genera are declining as a proportion of the dataset. This was apparent well before 2011 when we published the last atlas and continues to follow a similar downward trajectory (Figure 1). If anything, I suspect the rate of decline may be increasing. The big question then arises as to the cause. Is it simply that there are more records but no greater number of taxonomic recorders? Or, has there been a demographic shift?

Figure 1. Trend in the relative proportion of difficult species represented in the HRS dataset
To investigate this, I started to look at the composition of HRS recorders. We have previously noted that upwards of 50% of the data were supplied by just 21 recorders! The actual proportions bounce about quite a bit on a yearly basis so I looked at the contributions made by the top ten and top 20 recorders in any one year (Figure 2). This tells a fascinating story. All 20 recorders started to contribute between 1976 and 1992. In other words, the longest serving have been contributing for nearly 40 years and the youngest for 22 years! There were two big influxes, one in 1976/7 and a further recruitment in 1983-1985. Thus, the bulk of the major contributors to the scheme have been doing so for 30 years or more. Many on these recorders contribute between 500 and 1000 records per year, as shown in Figure 3 which depicts the contributions of the top 5 recorders. This figure shows how contributors data fluctuate quite substantially, reflecting rising and waning interest or the natural pressures of life.

Figure 2. Contributions to the HRS by the top 20 recorders over the period 1976-2013

Figure 3. Levels of data contributions by the top five contributors to the HRS. RM is 'Recorder 2'

If, however, one looks at the top 20 contributors each decade from 1976 to 2013 (i.e., 1976-1980; 1981-1990; 1991-2000; 2001 - 2010; and 2011 - 2013) the picture is very different (Figure 4). True, the same principle names are there, but the graph shows how major recorders only make a major contribution for a relatively short period of time. Critically, however, those recorders who started in the 1970's and 1980s have continued to form the nucleus of the Recording Scheme for much of the time. The data for the period 2011 to 2013 are misleading because there are several datasets that have not been updated since the call for records in 2009/10. Even so, the numbers of active new recorders are very encouraging and include at least 10 alumni of the training courses we have run in the past five years. This is most encouraging because the courses were intended to recruit replacements for the 1970s and 1980s cohorts and appears to be doing precisely that.

Figure 4. Contributions by recorders according to decade when they first became a major recorder.
The bigger question remains as to any changes in the types of data we are receiving. I think we can say with some confidence that the historic foundations of the scheme are slipping away. These were people who used Stubbs and Falk, and generally did all taxa. Many of the new recruits are equally well trained and also use Stubbs and Falk across all taxa. But, it seems likely that the absolute numbers of records entering the scheme has dropped in recent years because although new recorders have been recruited, the older ones who provided big blocks of data are less active. We can see this from Figure 5. It therefore seems highly likely that the composition of the dataset is changing, at least in the short-term. Its prognosis for the future is less clear, because we do seem to be recruiting good numbers of people who are versed in the skills needed to deal with difficult genera.

Figure 5. Numbers of records submitted to the HRS by conventional means, with the added contribution from photographs.

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