Wednesday, 11 February 2015
Insect collection - a philosophical question
Comments on a recent post in the UK Hoverflies Facebook page raise some important questions about the practice of retaining specimens. I hope the following will help to set some perspective.
The dataset held by the HRS comprises a mixture of field observations and preserved specimens. There would be very few records prior to 1976 without the collections of long-dead entomologists. Indeed, this is true for most datasets involving invertebrates. The one problem with museum collections is that they tend to be dominated (proportionally) by 'scarcer' species and by species that are tricky to identify. This creates an unhelpful imbalance that means that pre-1976 data are not ideal in presenting an image of what the hoverfly fauna looked like in the past. The one thing we do know is that certain species were regarded as 'prizes' (e.g. Volucella zonaria). Some data from this period are definitely helpful in reconstructing our knowledge of particular species. Anybody wanting to see this in action should look at two papers Stuart and I published on Volucella inanis and V. zonaria.
Many of the species that were most prized were big and bold (e.g. Callicera aurata). It is now possible to read the accounts of field trips by one of the early Dipterists and then actually hold the specimen the describe taking - which is an amazing link back in history.
Fast speed forward to 1976. Between 1976 and around 2009 the data held by the HRS was primarily supplied by people who at least partially retained specimens. Over 50% of the data were supplied by around 20 people. Those people generally record all taxa - in other words they tackle difficult genera such as Cheilosia and Pipiza. Having voucher specimens is essential if there are questions about a species' identity or if there is a split. Even experienced recorders make mistakes and being able to check is helpful. Only yesterday I spent the afternoon checking the IDs of specimens forwarded for verification. Not all were right, even from very experienced recorders. So, we must assume there are dodgy records in the dataset (some mine I expect).
The degree to which records are dodgy is often difficult to tell, but I have four species in mind where I think the maps definitely include significant misinformation: Lejogaster tarsata, Platycheirus immarginatus, P. nielseni and possibly Eristalinus aeneus. In the case of the Platycheirus I think we will have to restrict maps to cases where males have been recorded - females are too readily confused with others. This means that we will only get a realistic picture from specimens.
That leaves another 50% of data. What I have found is that there is a strong separation between the records of the nucleus who retain specimens and the remainder of the data, with far fewer records of tricky species/genera, and far more of species that can to a greater or lesser degree be identified from photographs or in the wild. Of course, we do get small blocks of data from people who work all taxa but do relatively little recording, so the data are not simply dominated by recorders who don't tackle tricky species. These data exclude lists where I take one look and say 'Chinnery' - there are ways of telling how recorders behave and the sources they use. They also exclude lists where it seems to me that the author has not used the key or bothered to check on a species' distribution - the presence of Scottish or coastal species in a list for a dry southern grassland is a fair indication!
So, moving on to the era where the mantra is: take nothing but photos and leave nothing but footprints. I am just finalising an analysis of species covered by photographs over 2014. That highlights just over 130 species (I have excluded a few photos of rare animals that were posted because I know they will arrive via lists supplied by the author). I also have an analysis of what has not been identified - no great surprises - dominated by Cheilosia, Pipiza, Platycheirus, but also including lots of Syrphus and Eristalis. So, bearing in mind this dataset comprises over 10,000 records (all records extracted from internet sources in 2014), there is a new influence on the dataset that will have to be taken into account when data are analysed for trends.
Based on past analysis of photographic records, I reckon that maybe 150 species will be recorded in this way, but that no more than 10 species will dominate the data, and no more than 35-40 will occur in sufficient numbers to perform any year-on-year analysis. Whether numbers will be sufficiently big to undertake latitudinal analysis remains to be seen, but I suspect the list will be depleted further.
We therefore hit the point where one must ask the question 'is it necessary to retain specimens?' If one wants to understand what is going on in the natural environment there is a need for quantitative data. In broad terms, that means trapping (and killing). But, trapping is fairly indiscriminate and does not necessarily cover all taxa. Also, trapping can kill large numbers of 'rare' species before this is detected. In the case of poorly known taxa this may never be detected. So, although trapping has its place, it has many drawbacks. If trapping is used to sample a narrow spectrum of animals then what happens to the by-catch? Bearing in mind this can be voluminous, the chances of it being tackled by a specialist are small. BUT, the data are quantitative and can probably be repeated at suitable intervals, thus forming a long time-series. One of the best examples of this is the Rothampstead moth survey. Jenny Owen's malaise trap also produced a really valuable time-series from her Leicester garden. These are rare, but valuable resources, and anything Government funded is under threat, so may not be available in future.
The Rothampstead programme has already been cut. Its loss would be catastrophic because it has highlighted a terrible decline in moth populations. Those changes are not down to retaining specimens - they are a mixture of climatic factors and anthropogenic changes to the countryside. Similar declines can be detect for many other taxa, including hoverflies. About 40% of our hoverfly fauna is in decline. We know this from the HRS dataset, which is supplied by a mixture of lethal and non-lethal sources, collected largely in an ad-hoc manner. These data are not ideal, but they are the best we have.
So, we now return to the question of retaining specimens in this modern World. A relatively small number of people retain specimens and many of them contribute extensive lists to the HRS. My guess is that around 150 people across Britain retain any level of specimens, and most retain very little. The contribution they make to the dataset is considerable, however. Perhaps not every specimen needs to be retained, but overall the impact of specimen retention is negligible. Conversely, the impact of the contribution to the dataset is considerable. Like it or not, we actually need people who are prepared to retain specimens and are driven by this interest. If we rely on non-lethal techniques then we will see a diminution in the value of the dataset.
It is therefore important to put specimen retention into context. Anybody who has watched social wasps hunting will know that they are voracious killers. A single nest may kill many tens of thousands of insects. Stuart and I did a bit of work in a small wood in Northamptonshire a few years ago that showed there was a strong probability of about 1 wasp's nest for every 1.5 ha of woodland. (i.e. around 40 nests in 60ha). That mounts up to a huge volume of invertebrate biomass. So social wasps are clearly important regulators of invertebrates. They happily munch hoverflies and if they have the same abilities of Anthrenus (museum beetle) my bet is that they take rare species disproportionately. So, our active Dipterist, working over the year, probably equates in impact to little more than a few workers within a social wasp nest, spread over a much larger area.
Ah, I hear you say, but if the 'collector' did not collect, then there would be more insects. TRUE! FRACTIONALLY! But also there would be CONSIDERABLY less data.
So let us move on to the take nothing but footprints argument. No hoverflies were killed in the making of this day out? Well, maybe. But if you drive to your venue that may not be so. We know that huge volumes of insects are killed in collision with cars. So, those who choose not to take specimens but enjoy watching wildlife in special places are also taking an informed decision to kill. It is just that they do so indiscriminately and with little knowledge of what they are doing.
I have had this debate with several proponents of this philosophy and am amazed by the answers they give - very largely about the fact that this improves their quality of life and the death of the insects they kill on the road is not intentional. How can this be? After all, they know that cars kill insects and will be irritated by the splat marks on the windscreen when they impair visibility. So, I fear, anybody who uses powered transport to conduct their hobby is having a negative impact on insects. Who knows if their victims are common or rare? The result is the same, but there is a difference between this approach and that of the entomologist who retains specimens. One generates partial data and the other more comprehensive data. Maybe this is a broad generalisation, but I think the key philosophical question relates to the contribution the deaths of insects make to our knowledge of insect ecology.
I therefore hold the view that the immoral issue is not about whether or not specimens are retained; it is about the degree to which we pursue our interests without making a contribution back to the wildlife we love. Detailed recording at whatever level can make a difference in highlighting the plight of wildlife. At least with robust data there is something to influence politicians and decision-makers. The biggest threat to wildlife is arguably the loss of taxonomically competent recorders whose contributions are essential if we are to track the trajectory of wildlife abundance.