Using data to interpret changes in the UK’s biodiversity

This article has been adapted from that which first appeared in the British Ecological Society’s Bulletin, December 2006.

Information about the distribution and abundance of species and habitats is vital if we are to make wise and informed decisions to help protect our wildlife. The biodiversity of the UK is relatively well recorded and it is estimated that up to 60,000 people are involved in collecting this information (Co-ordinating Commission for Biological Recording (CCBR) report 1995). Most of these people are volunteers and organise themselves through many national recording schemes and societies. The UK government, through its conservation agencies, and local government and conservation and wildlife-related NGOs also collect biodiversity data and one of the principal elements for the collation and interpretation of this data is the network of Local Records Centres.

The NBN aims to make as much wildlife information as possible available via the NBN Gateway.  The NBN Gateway helps the information to be quickly and easily accessed for analysis and interpretation and it has recently been used by the Joint Nature Conservation Committee (JNCC) to collate trends in species. Whilst there are many good sources of information concerning trends in particular groups (e.g. birds, butterflies, moths), this is the first attempt to bring this all together so that questions can be asked across taxonomic groups.

The Wildlife Statistics web-site collates information from two types of sources:

• Existing surveillance schemes, such as the British Trust for Ornithology's Breeding Bird Survey or the Butterfly Monitoring Scheme, which already publish trends for particular groups
• New analysis of information collected by National Recording Schemes and made available via the NBN Gateway.

Schemes such as the Breeding Bird Survey are based on systematic sampling designed to give statistically robust trends in abundance of species over time. General biological recording schemes are rather different. They collate observations of the presence of species only (i.e. usually with no reliable indication of abundance and no way of detecting where and when a species was absent!) from many different sources including field observations of volunteers and information from publications and museum collections. The non-systematic, ad hoc nature of the sampling means that there are potentially spatial and temporal biases in collection effort which makes it much more difficult to extract trend information. Consequently, only fairly gross changes in range or frequency are likely to be detected and the confidence intervals associated with the results are usually wide.

Never the less, methods have been developed to produce trends from data available from the NBN Gateway for nearly 5,000 species across a variety of National Recording Schemes including mosses, ferns, flowering plants, molluscs, spiders and a number of insect groups. An initial classification of the results across this wide range of species suggests that slightly more species are increasing than decreasing.

Proportion of 4,822 trends classified as “Increasing” or “Decreasing” if the rate of change is such that it would lead to a change of at least 25% in range or abundance if it continued to operate over 25 years. Otherwise it is classed as “No change”.

A couple of examples will provide a flavour of the data and analysis behind this and the way in which data from the NBN Gateway can be presented and interpreted.

The Ruddy darter dragonfly (Sympetrum sanguineum (Müller, 1764) (Odonata, Libellulidae) is a species which shows a strong increasing trend, both in the frequency of recording and a northward increase in range. Frequency of recording can be measured by the proportion of 10km squares of the National Grid in which it was recorded in a given year by the British Dragonfly Society’s Dragonfly Recording Scheme, as a percentage of all the squares sampled by the scheme in that year (Spearman rank correlation = 0.844, p<0.001). 10km squares recorded before and after 1989 (the year by which half the records submitted to the scheme were received) by the Recording Scheme can also be mapped with different symbols indicating squares in which the species was only recorded from the period up to 1989, in both periods or only since 1989. The map suggests that the range of the species has expanded northwards and to a lesser extent westwards since 1989.

  
Change in the frequency of recording and the range of Sympetrun sanguineum.

Orange symbols on the map indicate 10km squares where it was recorded up to 1989, but not since, green if it was recorded only since 1989 and blue if it was recorded in both periods.

By contrast, using data from the British Arachnological Society’s Spider Recording Scheme, the spider Allomengea scopigera (Grube, 1859) (Araneae, Linyphiidae) shows a decline in the frequency with which it has been recorded (Spearman rank correlation = -0.842, p<0.001), but there is not such a clear pattern to the range map. There is a tendency for losses to be concentrated in the more south-easterly part of its range and it has almost disappeared from the south and east coast of England, whilst new squares are mostly in the north and west. This may be due to more recording in these areas in recent years rather than a range expansion, but does suggests it is not being lost from these areas.

Change in the frequency of recording and the range of the spider Allomengea scopigera. The year by which 50% or records had been received by the Spider Recording Scheme is 1991.

  
Another area of investigation has been the potential impact of climate change on species distributions. Here is an example using data from the Hoverfly Recording Scheme. Two closely related species, Chrysotoxum arcuatum (L., 1758) and C. cautum (Harris, 1776) (Diptera, Syrphidae) have almost mutually exclusive distributions in Great Britain. C. arcuatum occurs in the north and west, whilst C. cautum occurs in the south and east. Environmental niche models were fitted for each species separately using the Desktop GARP package (Genetic Algorithm for Rule-set Production – a machine learning algorithm) with environmental layers including topography, land cover and weather variables. These were fitted at 5km square resolution to observations from England and Wales from 1990 onwards. Models were fitted to half of the available data, selected randomly, and tested against the other half. Well fitting models were achieved in both cases (Area Under the Curve from Receiver Operating Characteristic analysis of the predicted distribution against the test data: AUC = 0.857 for C. arcuatum and AUC = 0.900 for C. cautum).

Predictions were also made with the weather variables for 1991–2000 used to fit the models replaced by the corresponding variables predicted for 2020 using the medium-high emission scenario. Comparison of these predictions suggest that C. arcuatum would be expected to contract in range, tending to retreat to higher altitude, whilst the range of C. cautum would be expected to expand through mid-Wales to north west England and become more widespread in north east England. The predicted changes in the altitudinal distribution of C. arcuatum suggest almost complete loss of the species at lower altitudes in England and Wales.

These changes in range, both geographical and altitudinal, should be detectable by a general purpose data collation scheme like the Hoverfly Recording Scheme, and the data against which to test such predictions should become available over time via the NBN Gateway.

Number of 5km squares, classified by mean altitude, in which C. arcuatum is predicted to occur in England and Wales by Desktop GARP models using weather variables for 1991–2000 and the same variables predicted for 2020 medium-high emission scenario.

These sort of analyses barely scratch the surface of what is becoming possible given the increased availability of biodiversity data brought about by the NBN Gateway. What is vital however, is the passion of, and ongoing biological recording by, the organisations and individuals who are out in the field doing the hard work. Only if this continues will we be able to monitor changes to our nation’s wildlife in the future.

If you are interested in further information or other worked examples please contact Stuart Ball, Chief Analayst at JNCC at Stuart.Ball@jncc.gov.uk