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Butterfly records using data in conservation
Introduction The aim of this paper is to provide an overview of the ways in which butterfly records are being used in conservation
and ecological research, not at the local, site-based level, but in a wider context.
There are two distinctive types of butterfly data being collated in Britain and Ireland today. Distribution records form the majority of butterfly records held by Butterfly Conservation, local biological records centres and the national Biological Records Centre. Such records are not collected using a standardised methodology, although there are data standards. Abundance indices are based on the transect recording method developed by the Institute of Terrestrial Ecology (ITE). This recording is standardised in relation to time and weather, and data are collated nationally by the Butterfly Monitoring Scheme and by Butterfly Conservation.
Distribution data Compiling databases of butterfly records covering wide geographical areas enables us to put local
populations into context. At the national level, analysis of the 10 km square distributions in the first comprehensive atlas (Heath et al.1984) showed that almost half of the 59 resident species are
threatened or already extinct. Since 1995, Britain and Ireland have been re-surveyed by the Butterflies for the New Millennium project (Asher et al. in press). This project and other species-specific research
have shown that many butterflies have continued to decline at alarming rates. The range of the Pearl-bordered Fritillary (Boloria euphrosyne), for example, has declined by more than 50% during the last 15
years.
In general, the declining species are those that are already scarce and which have highly specialised habitat requirements. They are the butterflies
of chalk downland, coppiced woodland, unimproved damp grasslands and bogs. Their declines are due to habitat destruction and deterioration, and the consequent effects of increasing fragmentation and isolation.
National distribution data also show that some 15 species are expanding, although almost all of these were already common and widespread
in southern Britain (e.g. the Comma, Polygonia c-album, whose range has moved about 200 km northwards since 1982). Most are species of the wider countryside that are still able to find suitable habitat in the
modern, farmed landscape. Climate change is believed to be the most important factor behind these recent expansions.
These data have been used to measure rarity and trends in distribution for the assessment of conservation priority. Warren et al.
(1997) analysed the 1984 atlas data to draw up a revised "red list" of butterflies in the UK. This has set the agenda for Butterfly Conservation's work over the past few years, notably in the production of Species
Action Plans for twenty-two butterflies considered to be national priorities.
The populations of butterflies in Britain and Ireland have also been given a wider context by a new European Red Data Book, compiled by Butterfly
Conservation and Dutch Butterfly Conservation for the Council of Europe (Swaay and Warren 1999). Six species resident in Britain (including two that are also resident in Ireland) were listed as Species of European
Conservation Concern: the Lulworth Skipper, Large Blue, Duke of Burgundy, Marsh Fritillary, Scotch Argus and Large Heath.
Also at the international scale, Parmesan et al. (1999) reviewed the change in range of European butterflies over the past 30100
years and provided the first large-scale evidence of pole-ward shifts in the entire ranges of species. In keeping with the predicted response to global warming, northward shifts in range were recorded for over 60%
of a group of 35 non-migratory species for which sufficient data were available, whilst only 3% had shifted south. Species on the move included the White Admiral (Limenitis camilla), Marbled White (Melanargia galathea) and Gatekeeper (Pyronia tithonus),
all of which are also expanding northwards in Britain.
Research applications Databases of distribution records such as that compiled for the Butterflies for the New Millennium project
present a very wide range of opportunities for ecological research. One ongoing study is examining the causes of recent range expansions and the potential consequences of global climate change. Hill et al. (1999) developed models to predict the distribution of the Speckled Wood (Pararge
aegeria) using climate variables that are likely to affect the butterfly. The models worked well, particularly when habitat availability was taken into account. They were then run forward in time to predict the
distribution of the Speckled Wood under various climate change scenarios. This work is now being expanded to include other species, such as the Gatekeeper and Ringlet (Aphantopus hyperantus), and the early
indications are that the ranges of these species will continue to expand northwards in Britain as the climate warms.
Another elegant study has developed a new approach to estimating rates of decline. Coarse grain (e.g. 10km square resolution)
distribution maps have been used to measure changes in butterfly distributions. However common species, which may have many populations per occupied square, have the potential to decline considerably within squares before they are lost from entire squares and register on a distribution map. To try to quantify this effect, Cowley et al.
(1999) used data on the actual size of habitat areas used by butterflies. The distribution data for some of the rarer species is now so comprehensive, that all known colonies have been mapped and the entire area of
land used by a species in Britain can be measured or estimated. These total national flight areas are very small, and several were less than 3km². Using the IUCN categories for threat based on area of occupancy, all
13 of the species examined in this way would be classified as critically endangered, endangered or vulnerable. Using 10km square maps, only three species would qualify (in the lowest risk category).
Developing the idea further, the authors then examined the flight areas of more common butterflies that were present in a study area in
north Wales. Butterfly densities were mapped in different habitat types and declines estimated by comparisons with the extent of these habitats in 1901. The results revealed that many common species (e.g. the Small
Copper, Lycaena phlaeas, Brown Argus, Aricia agestis, and Common Blue, Polyommatus icarus) had declined as fast in this area as rare species have nationally.
Abundance indices The Butterfly Monitoring Scheme (BMS) co-ordinates transect recording to produce annual indices of the relative
abundance of species across the UK. Although these indices are not representative of wider countryside, there are many important applications.
The indices provide a measure of abundance that is not unduly influenced by changes at individual sites. Therefore, wider influences on butterfly
abundance (most notably the weather) can be separated from site-specific effects, such as habitat management. Annual indices can be compared to assess trends in species abundance over time, and long-term trends
(such as those associated with climate change) can be distinguished from fluctuations caused, for example, by short-term weather events. In addition, the BMS data set has provided valuable information about
butterfly phenology, voltinism, migration and local distribution changes.
David Roy and Tim Sparks (in press) at ITE have recently shown that the flight periods of many butterflies are starting earlier in the year and
going on for longer now than they were in the 1970's when the BMS commenced. This trend is in accord with research showing earlier nesting and migration in birds and an extended growing season and first flowering
dates in plants.
Many transects are recorded which do not form part of the official BMS but, until recently, these were only collated locally. Now Butterfly
Conservation and the Ministry of Agriculture are collating this data nationally to assess the impact on butterflies of agri-environment schemes such as the Environmentally Sensitive Areas and Countryside Stewardship.
Conclusions Although this has been only a brief review, it is clear that butterfly records present an extremely wide range of
opportunities to further the understanding and conservation of our butterfly biodiversity. Many of these approaches are new, and further initiatives will undoubtedly continue to be made to fully utilise the data
gathered by the great army of amateur and professional naturalists in these islands.
References
Asher, J., Warren, M., Fox, R., Harding, P., Jeffcoate, G. and Jeffcoate, S. (in press). The millennium atlas of butterflies in
Britain and Ireland. Oxford University Press.
Cowley, M.J.R., Thomas, C.D., Thomas, J.A., and Warren, M.S. (1999). Flight areas of British butterflies: assessing species status and decline. Proceedings of the Royal Society of London B
266: 1587-92.
Heath, J., Pollard, E., and Thomas, J.A. (1984). Atlas of butterflies in Britain and Ireland. Viking, Harmondsworth.
Hill, J.K., Thomas, C.D. and Huntley, B. (1999). Climate and habitat availability determine 20th century changes in a butterfly's range margin. Proceedings of the Royal Society of London B
266: 1197-206.
Parmesan, C., Ryrholm, N., Stefanescu, C., Hill, J.K., Thomas, C.D., Descimon, H., Huntley, B., Kaila, L.., Kullberg, J., Tammaru, T., Tennant, J.,
Thomas, J.A.., and Warren, M.S. (1999). Poleward shifts in geographical ranges of butterfly species associated with regional warming. Nature 399: 579-83.
Roy, D.B. and Sparks, T.H. (in press). Phenology of British butterflies and climate change. Global Change Biology.
Swaay, C. van and Warren, M.S. (1999). Red data book of European butterflies (Rhopalocera), Nature and Environment, No. 99
. Council of Europe, Strasbourg.
Warren, M.S., Barnett, L.K., Gibbons, D.W., and Avery, M.I. (1997). Assessing national conservation priorities: an improved red list of
British butterflies. Biological Conservation 82: 317-28.
Richard Fox Butterflies for the New Millennium, Co-ordinator, Butterfly Conservation, PO Box 444, Wareham, Dorset BH20 5YA. Tel:
01929-400209 email: rfox@butterfly-conservation.org
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