6 INDICATOR SPECIES The idea that a group of species can be used as indicators to assess and monitor environmental quality and change is a simple and attractive one and has been successful in a number of cases. The range of species is considerable and they can be used in a variety of ways. The first group are those which are used to describe and classify communities. A good example of this is phytosociolagy, the National Vegetation Classification for instance. Here an assemblage of species is used to distinguish one community from another. Further sub-divisions of the main community and the relationships between vegetation types can be defined by considering the presence and absence of other (indicator) species. A second group of species is used to assess quality and to monitor environmental change. Perhaps the best example of this is provided by freshwater communities which are used to assess river water quality. Here there have been three approaches; first. a simple biotic index in which the differential responses of species to a pollutant is used to asses quality. Secondly, diversity indices (species richness and equitability) provides a more refined approach. Finally, the most detailed approach relates community structure to environmental variables (RIVPACS) to provide target communities against which physical and chemical stresses can be assessed. The group of indicator species which are used to identify ancient woodland or to date hedgerows is similar to a biotic index. In these cases persistence and susceptibility to disturbance are the variables which determine the presence or absence of these species. Finally there are species which have a high conservation value. The value is recognised in various listings. Red lists and RDBs are examples although strictly they are mainly with threatened species, not those of conservation value as such. The presence of one or more of these species at a site gives it a high conservation value. Sites may be valued both as examples of particular biotopes and as places where certain rare or notable species occur. Generally indicator species have certain characteristics. They are taxonomically and ecologically highly diversified. They are restricted to the habitat, and are easy to bbserve, identify and to sample. Above all, they must show a direct and predictable response to change. The heathland indicators used by Moore (1962) were primarily chosen to assess the effects of isolation. On isolated heaths, which were in general smaller than the less isolated, the chance of extinction was higher and the possibility of recolonization reduced. Hence, as Moore showed, fewer heathland species occurred on the isolated heaths than on the others. What are the possibilities of developing a set of indicator species far heathland? First, there is little need to develop a list to describe and classify the vegetation. Secondly, those species which are rare and notable and which can be used to assign conservation value are well known. However, ta draw up a list of species which can be used to assess habitat quality is more difficult. For this last named objective to be met it is likely that an examination of diversity or community structure will be required, in effect developing an approach similar to RIVPACS. Indicator species are used to 20 FIGURE 19 Frequency diagrams of the distribution of records for both heath and generalist species. The three categories are; 0 = No heathland within the 4ha'square; 1 = less than 50% of the square heathland; 2 = 50% or more of the square heathland. Ch-bpicm tmdlm pynfiosomanyrphula 60 50 g: F 20 10 0 0 1 I 2 c11 c11 Pl*us agus 0 1 2 0 1 i Cll c11 3- !m- I? w- 7 0 1 I I 0 1 2 Cll Lgataagilis LacataViVipara 25 M 5 0 1 3 0 1 2 c11 c11 assess quality and change where these themselves are difficult to measure. Howeverl when it becomes difficult to record community structure it may be simpler to measure habitat quality directly. To some extent this must be the case for heathland as it will be simpler to inspect the vegetation than to record the presence of indicator species, especially if these are invertebrate animals. Invertebrates which are easy to collect are often difficult to sort and identify. When indicator species work well they indicate changes which are otherwise difficult to observe, such as a pulse of a pollutant in a river or a very long period without disturbance in a woodland. In conclusion we suggest that lists of species of possible value as indicators on heathland be assembled and an attempt made to develop a set of species useful in assessing habitat quality. This is likely to be a prolonged and iterative process. 21 7 ACKNOWLEDGmS We are grateful to the Dorset Environmental Records Centre for their collaboration in extracting and supplying records for the Dorset Heathlands. We are particularly grateful to Richard Surry (Keeper of Records) and Brim Edwards . The Royal Society for the Protection of Birds, South-west Region supplied records of heathland birds and we are grateful to Dr Mark Robbins assembling these records and preparing them. 22 8 REFERENCES Chapman, S.B., Clarke, R.T. & Webb, N.R. 1989. The survey and assessment of heathland in Dorset for conservation. Biological Consemation, 47* 137-152. Chapman, S.B. & Rose, R.J. 1994. Changes in the distribution of Erica ciliaris L. and Erica x watsonii Benth. in Dorset 1963-1987. Watsonia. 20, (in press). Gilpin, M.E. & Hanski, I. 1991. Netapopulation Dynamics: Empirical and Theoretical Investigations. Academic Press, London. MacArthur, R. H, & Wilson, E.O. 1967. The Theory of Island Biogeography. Princeton University Press, Princeton. Wan, A. & Pearman, D. no date. Endangered Wildttfe in Dorset. Dorset Environmental Records Centre. Dorchester. Moore, N.W. 1962. The heaths of Dorset and their conservation, Journal of Ecology, 50. 369-391 Prendergast, E.D.V. 1991. The Dragonflies of Dorset. Dorset Natural History and Archaeological Society, Dorchester. Prendergast E.D.V. & Boys, J.V. 1983. The Birds of’Darsst. David & Charles, Newton Abbot. Ratcliffe, D.A. 1977. A Nature Conservation Review. Cambridge University Press, Cambridge. Spellerberg, I.F. 1991. Biageographical basis of conservation. In Spellerberg, I.F., Goldsmith, F.B. & Morris, M.G. (eds). The Scientific Ranagernent of Temperate Communities for Conservation. Blackwell Scientific Publications. Qxfwrd. Thornas, J.A. & Webb, N.R. 1984. Butterflies of Dorset. Dorset Natural History and Archaeological Society, Dorchester. Webb, N.R. 1990. Changes an the heathlands of Dorset, England, between 1978 and 1987. Biological Consermation, 51, 273-286. Webb. N.R. & Haskins. L.E. 1980. An ecological survey of heathlands in the Poole Basin, Dorset, England in 1978. Biological Conservation, 17, 281-296. Webb, N.R. & Hopkins, P.J. 1984. Invertebrate diversity on fragmented Calluna-heathland. Journal of Applied Ecology, 21, 921-933. Webb, N.R. & Vermaat, A.B. 1990. Changes in vegetation diversity on remnant heathland fragments. BZoZogicaZ Conservation, 53, 253-264. 23 INSTITUTE OF TERRESTRIAL ECOLOGY (NATURAL ENVIRONMENT RESEMCH COUNCIL) Project T08079LI English Nature/NERC Contract Habitat Fragmentation and Weathland Species: Supplementary Report N R Webb Fumebrook Research Station Wareham Dorset BA20 SAS CONTENTS Page SUMMARY 3 1 INTRODUCTION 4 2 A rmRTHER STUDY OF THE STATUS OF 5 WORE'S INDICATOR SPECIES 3 SPECIES OF POSSIBLE USE As INDICATORS 12 3.1 Introduction 12 3.2 Heathland spiders 12 3.3 Lepidoptera 13 3.4 Ground beetles 19 3.5 Herniptera - Heteroptera 19 3.6 Orthoptera and related Orders 21 3.7 Heathland plants 21 GENERAL POINTS ON INDICATOR SPECIES 24 ACKNOWLEDGEMENTS 25 6 REF"CES 26 2 SUMMARY 1. As a result of additional data becoming available, a further analysis of the occurrence of eight heathland indicator species in 1960 and at the present time has been made. 2. This analysis shows little change from the overall pattern reported by Webb & Rose (1994). The largest heaths still contain all 8 indicator species. There have been Losses from the smaller isolated heaths with the generalist species showing marked declines. The smaller heaths tend to be more dynamic, both losing and gaining species. 3. Lists of species of possible use as indicators are presented. These cover spiders, butterflies and moths, ground beetles, bugs and plants. 3 1 INTRODUCTION In the previous report (Webb & Rose 1994) an analysis was made of the occurrence of eight heathland species in relation to patch size and isolation. The eight species chosen were those used by Moore (1962). The repetition of Moare's exercise confirmed his finding that where heaths were more isolated they tended to lack characteristic species, In addition, the prediction made by Moore that the small and isolated heaths would continue to lose heathland species was confirmed. Moore used only eight indicator species all of which were animals. It is of interest to consider what other species could be used both to examine the effects of fragmentation and isolation and also to assess habitat quality. This supplementary report presents details of some further analyses. First. because additional data are now available. the basic exercise has been repeated and secondly, a wider range of species, mostly invertebrates, has been examined with a view to developing a set of heathland indicator species. 2 A FURTHER STUDY OF THE STATUS OF MOORE'S INDICATOR SPECIES Webb & Rose (1994) presented a table (Table 4) comparing the presence between 19-59-60 and 1980-93 of Moore's 8 heathland indicator species on twelve heathlands. This comparison was made almost entirely from records available from the Dorset Environmental Records Centre. Since that comparison was made, a number of other records have been located. First, it was realised that the 1980-93 records were deficient particularly for the Common and Sand Lizards.