Journal of Insect Conservation 5: 131–139, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.
An approach to interpretation of lists of insects using digitised biological information about the species Martin C.D. Speight1,∗ & Emmanuel Castella2 Research Branch, National Parks & Wildlife, 7 Ely Place, Dublin 2, Ireland 2 Laboratoire d’Ecologie et de Biologie Aquatique, Universit´e de Gen`eve, 18 chemin des Clochettes, CH – 1206 Geneve, Switzerland ∗ Author for correspondence (e-mail:
[email protected])
1
Received 4 May 1999; accepted 11 May 2001
Key words: species pool, habitat management, Syrphidae, Diptera, biodiversity
Abstract Predicted species lists are generated from regional species pools, coupled to codified habitat, microhabitat and biological trait data for the species. At site level, habitat association data are used to tailor the predicted list to site conditions and comparison between predicted and observed species lists is used to explore elements of site quality and site management options involving microhabitat and trait data for the species in the process. It is pointed out that this approach makes possible the interpretation of insect species lists by non-specialist site managers. At larger geographic scales, attributes of regional lists are identified. Throughout, the approach is considered in the context of its potential to contribute to resolution of issues relating to maintenance of biodiversity in Europe and the taxonomic group employed is the Syrphidae (Diptera). Introduction In the field of environmental management ecologists need predictive tools. Their appraisal of problems relating to maintenance of biodiversity has too often been of limited application, because of heavy dependence on data for flowering plants and/or vertebrates, which together comprise only a minor element of European biodiversity. Invertebrates comprise more than 70% of Europe’s biodiversity. Further, more reliance has usually been placed on statistical techniques rather than on biological information, in attempting to grapple with these issues. The rich store of potentially relevant biological data can then remain largely unrecognised and untapped. This is particularly true of invertebrate data, perhaps unsurprisingly, given the small number of invertebrate specialists, the scattered nature of the information and the general perception that there are too many invertebrates for them to be handled in any meaningful way. Finally, there is the problem that criteria currently employed in investigating biodiversity issues, such as
‘naturalness’, are extremely resistant to assessment, or, like ‘uniqueness’ and ‘representativeness’, are almost impossible to combine into some holistic evaluation system. Biodiversity issues occur within a geographical context, which ranges from local to global. This geographical context is here referred to as the ‘region’ within which a particular biodiversity issue is addressed. Use of the term ‘region’ in this way does not imply any specific geographic scale, or degree of ecological or biogeographical homogeneity, but rather a piece of territory which can be adequately defined on a map. As used here, its essential feature is that a reliable species list is available for it or can be compiled for it. In practise, most regions are defined by administrative considerations, either local or national. Employing Syrphidae (Diptera) as the taxonomic group involved, the aims of this text are to demonstrate: (a) the use of the predictive capacity of the species pool approach, using species lists from parts of western Europe,
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(b) the use of databased information about the species, as a tool for interpretation of species lists, (c) the synergistic interaction between (a) and (b). The species pool concept is essentially that the species occurring in part of a region comprise a subset of the fauna (or flora) of that region and so can be predicted from the regional species list, given certain provisos. The regional species pool is used to generate predicted species lists for sites, for comparison with lists of observed species derived from the same sites, and the databased biological information is used to compare attributes of the predicted and observed lists. The unit of biodiversity is taken to be the species and the unit of biodiversity maintenance is taken to be the habitat, as defined in European classification systems such as CORINE (Devillers et al. 1991). Maintenance of maximal biodiversity on a site is then regarded as maintenance, on that site, of a maximum number of the species associated with each habitat found on that site. Maintenance of maximal biodiversity on a site, in a given region, then becomes maintenance on that site of the maximum number of species that are predicted to occur in association with the habitats observed on that site and are known to occur in that region. Increasing attention has latterly been paid to the species pool approach in literature. Keddy (1992) and Zobel (1997) focus on prediction of community composition. P¨artel et al. (1996) and Caley and Schluter (1997) compare species richness at local and regional levels and Zobel et al. (1998) debate definitions and delimitation of species pools at various spatial scales. Species lists per se are not currently highly regarded as ecological tools. Yet there is a solid basis for asserting that reliable species lists are one of the most effective weapons in the ecologists’ armoury – in the case of invertebrates potentially far more potent in environmental interpretation than multivariate statistical analyses of relative abundance data. At present, tools for using species lists are under-developed, and generally concern only some minor sub-set of the species in any one list. One obvious example of such a subset is the species which may be consigned to some special ‘threat status’ category, as defined by IUCN (IUCN 1994), and so identified as deserving preferential treatment in national or local management programmes. The present text is focused on a procedure for employing entire species lists, in which the component species may be considered in various combinations according to which attributes they share, but attention is not confined to the species sharing one
attribute such as a particular threat status category. Although the procedure is amenable to the use of relative abundance data, its application will be explored here in presence/absence terms, because the simple species list is the form in which invertebrate inventory data are most frequently available (particularly at national or international scale). The large numbers of species involved, which have inhibited work with invertebrate species lists in the past, no longer represent a problem to potential users like site managers now that the data can be computerised and computers are so widely available. Today, it is the advantages of the existence of these large numbers of species that are more apparent, when each may act as an independent unit able to reinforce conclusions derived from others. Methods Careful selection of taxonomic groups, aimed at maximising the return from sampling and processing of data, is necessary when using invertebrate taxa as interpretive tools, because insufficient is yet known about many groups. Further, the available data are not accessible for many groups, there being very few published databases available in which biological information about the species has been digitised. In the case of the European syrphid fauna (hoverflies or flowerflies) the Syrph the Net database of European Syrphidae is available. The suitability of Syrphidae, for use in this sort of work, is considered by Speight et al. (1998). The Syrph the Net database The Syrph the Net database comprises an annually updated set of text files and spreadsheets. The text files are in MS Word and the spreadsheets use MS Excel. The most recent version of the files covers 500 of the ca. 800 species of European Syrphidae and contains spreadsheet files on: Macrohabitat associations (association with a habitat being coded according to whether or not a species develops in that habitat) of the species (macrohabitat = habitat sensu Devillers et al. 1991). Microsite features (microhabitat attributes) with which the larvae are associated. Biological traits of the species (adult traits, e.g. flight period; larval traits, e.g. trophic group). Geographical Range and threat status data for the species.
Interpretation of lists of insects These spreadsheets provide a matrix of 600 columns by 500 lines, i.e. 300,000 cells of digitised data, and can be used independently or in combination, as required. The information is coded into the spreadsheets using a simplified ‘fuzzy coding’ system (Castella & Speight 1996). The known syrphid fauna of the following European States is included in the database: Belgium, Denmark, Luxembourg, Netherlands, Republic of Ireland, United Kingdom. The database also covers the syrphid fauna of northern Germany (defined by L¨ander), atlantic parts of France south to the Pyrenees (defined by D´epartements) and lowland (i.e. below 1000 m) Switzerland. The syrphid habitats occurring in these parts of Europe are also covered by the database, the habitat categories used following as closely as possible definitions employed in internationally agreed habitat classification systems, notably those of the CORINE system (Devillers et al. 1991) and the EU Habitats Directive (Romau 1996). Ensuring exact co-incidence between all habitat categories used in the database and those employed in these international systems is unfortunately not possible (Speight et al. 1997). Definitions of every variable, and every category of each variable used in the spreadsheets are provided in text file glossaries. Additional text files provide a set of species accounts of all syrphid species covered. Further information about the Syrph the Net database can be obtained from the following e-mail address:
[email protected]. Use of the Syrph the Net database Various regional lists are provided in the Range and Status file of the database, notably national lists for the countries covered by the database and a list for the Atlantic zone of Europe, but database users will, as a general rule, require to provide lists themselves, for the regions in which they are working, if they are to operate the procedures the database has been set up to facilitate. That is the case for the various parts of Ireland referred to in examples presented below. Beyond certain basic steps (outlined in Speight et al. 1998) which are more or less mandatory for initiating the process of database interrogation, there are no standard procedures for its use – so much depends on the particular character of individual enquiries. Variations in application are illustrated below. All examples invoke the predictive capacity of the regional species pool, but differ in other respects. The first three are based on data from a site in the Killarney National
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Park (Ireland), referred to as the OKR site (more information about this site is provided in Speight, 1997). In these examples, multiple predictions have been made, to show the result of basing prediction on lists from regions of different geographic scales. From smallest to largest, the ‘regions’ used are as follows: • the site itself (the OKR site) • the National Park (Killarney National Park) in which that site is situated • the county (Co.Kerry) in which the Killarney National Park is situated • the island of Ireland, in which Co.Kerry is situated • the part of Europe (the Atlantic Zone) in which Ireland is situated In the fourth example, species lists from parts of the Atlantic Zone that are of approximately the same geographic scale and status are taken as lists of observed species and compared with each other, using the regional list for the Atlantic zone in general as the species pool providing the basis for comparison. In the final example, the island of Ireland is taken as the region and the Irish species list is used as the basis for comparing attributes of the fauna of different Irish habitats. These examples focus on the following issues: (a) assessment of the performance of the ‘biodiversity maintenance function’ of a site (b) site biodiversity management (i) maintenance/enhancement of habitat quality (ii) introduction of new habitats (c) regional biodiversity management (i) identification of habitats with a high faunal diversity (ii) identification of habitats/microhabitats supporting high concentrations of ‘anthropophobic’ species Results 1. Assessment of the performance of the ‘biodiversity maintenance function’ of a site (an index based on differences between expected and observed species occurrences) The biodiversity maintenance function can be used as a measure of site quality. In combination with the species pool approach, this measure may be expressed as follows: if 100% of the regionally occurring species predicted to occur in a particular habitat are observed on a target site in that region, then the biodiversity
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Figure 1. The OKR-site species associated with three different habitats occuring on-site, shown as a percentage of the species with those same habitats in the species lists for ‘regions’ of different geograophical extent. Thus the first histogram column shows that 40% of the AZ species associated with the poorly-drained, unimproved pasture habitat occur on the OKR site, and the fourth column shows that these species represent 60% of the KNP species associated with this habitat. AZ = Atlantic zone of Europe; IRL = Ireland; Kerry = Co. Kerry; KNP = Killarney National Park; OKR = Old Kenmare Road site.
maintenance function is performing at maximum efficiency in that habitat on that site. Lower percentages of the predicted fauna are then taken to indicate poorer performance of the biodiversity maintenance function. In order to evaluate the performance of the biodiversity maintenance function in this way the following data are required: • a regional species list for the area in which the target site is situated • a species list for the target site • a list of the habitats occurring on the target site • the syrphid database. In western Europe, where landscapes have been so modified by man’s activities, it is arguable that no site can today be expected to support its full complement of predicted species and this has to be taken into account in rating its potential. In the example presented here, presence on-site of more than 50% of the species predicted to occur in association with a particular habitat observed there is taken to indicate that habitat to be in reasonable condition to support its associated biodiversity and presence of more than 75% of the predicted species is taken to indicate the habitat is in good condition.. There is no entirely objective method for deciding what is the appropriate cut-off point for assigning a site to some particular quality category. But whatever valuation system we use, they are all ultimately anthropogenic, there being no absolute
system for valuing nature in its various manifestations. The system employed here has the virtue of being simple, holistic and applicable across a wide range of circumstances. Figure 1 shows the proportion of the predicted syrphid fauna observed in three different habitats on a site in a National Park in SW Ireland. The figure is taken from Speight (1997). The faunal prediction for each habitat has been generated using four different geographic scales of ‘region’, so that four histogram columns are presented for each habitat type. Comparison between the four columns for one habitat shows the need to ensure that issues of biodiversity maintenance are considered within a specified geographic context – the proportion of the predicted fauna observed indicates that the site has a reasonable fauna for all three habitats, when considered solely within the context of the National Park as a ‘region’. But at the other end of the scale, when the observed site fauna is considered as a proportion of the fauna predicted for the Atlantic Region in general, its species representation is good only for blanket bog surface. 2. Site biodiversity management Identification of the habitats whose fauna is poorlyrepresented on a site might be recognised as an essential first step in any programme aimed at maintaining biodiversity, in that it highlights those habitats as
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requiring further investigation. However, it does not directly provide information on why the biodiversity maintenance function has a low value in those habitats on that site, or indicate what might/should be done to improve matters. These issues can be approached by comparing the requirements of the predicted, observed species with those of the predicted but absent species. The species’ requirements can be portrayed in terms of either their micro-habitat associations, their biological traits, or both.
species are feeders on living or moribund plant tissue. Of itself, this does not explain the generally poor representation of poorly-drained, unimproved pasture fauna on this site. But it does help to identify those habitat components that are potentially most urgently in need of remedial management, in this instance the ground flora of the site. In reality, it is recognised that this site has been over-grazed for many years and a current management objective there is to establish a less-damaging grazing regime.
2a. Maintenance/enhancement of habitat quality Figure 2 is based on the same site data as Figure 1, but in this case attention is confined to the fauna of the poorly-drained, unimproved pasture on the site. The observed fauna is shown as a proportion of the predicted fauna of a selection of poorly-drained, unimproved pasture micro-habitats. Again, four histogram columns are given for each microhabitat, the observed/predicted comparison being conducted at the same four geographic scales as in Figure 1. The dramatic differences shown in proportional representation, by faunas of different microhabitats, is by no means unusual. It reflects the reality that site management impinges at microhabitat level, not habitat level, a contention which will be alluded to more than once in this text. For explanation of the total lack of species whose larvae live within plant tissues of one type or another resort can be made to the traits data, revealing that the larvae of all of these
2b. Introduction of new habitats On some sites, biodiversity maintenance may be better served by transformation of one habitat into another, than by attempts to maintain or enhance existing habitat A habitat exhibiting a low value for the biodiversity maintenance function, identified as such using the approach outlined in the preceding paragraphs, is clearly a target for either enhancement or transformation. In the latter case there is need to consider the relative desirability of the alternative habitats. For convenience, the same site data are used for consideration of this issue, as have been used in the preceding paragraphs. However, the data on the observed fauna are employed somewhat differently. In considering the extent to which the species predicted for a habitat are represented on a site, only the species associated with that habitat are considered – species recorded from the site, but not associated with habitats found
Figure 2. The OKR poorly-drained, unimproved pasture species with the larval microhabitat associations ‘on herbaceous plants’, ‘in herbaceous plants (stems)’ ‘in herbaceous plants (bulbs)’, expressed as a percentage of the species associated with these same microhabitats in ‘regions’ of various geographical scales. Thus the first histogram column shows that more than 80% of the Atlantic zone species occurring as larvae on herbaceous plants in poorly-drained, unimproved pasture, occur on the OKR site. The eight vacant columns show that none of the species with larvae living in stems or bulbs of herbaceous plants, in this habitat, occur on the site. Abbreviations: as in Figure 1.
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Figure 3. The percentage of the Irish syrphid fauna associated with Quercus and Salix/Alnus forest habitats that would be predicted to occur on the OKR site were those habitats to be established there, basing prediction on species pools of ‘regions’ of various geographic scales. Thus, the first histogram column shows that c. 20% of the Irish species associated with Salix would be predicted to occur on the OKR site if Salix forest were established there, if prediction is based on the observed fauna of the OKR site. The third column similarly shows that c. 45% of the Irish scrub Salix fauna would be expected there, if prediction is based on the observed fauna of the Killarney National Park in general. Abbreviations: as in Figure 1.
there, are omitted from the assessment. In evaluation of the relative desirability of introducing the various alternative habitats to the site, all the recorded species are involved. The aim is to establish what proportion of the fauna predicted for each of the new habitats is either already supported by the site, or already reaching the site from elsewhere. The site concerned in the example contains neither Salix woodland nor Quercus woodland, these being the two alternative habitat types which might be introduced there by management. In Figure 3, the proportion of the Salix woodland fauna already occurring on the site is compared with the proportion of the Quercus woodland fauna already occurring there, taking various component habitats separately and in the context of regional species pools of different extent. In general terms, the comparison demonstrates that the Salix fauna can be expected to establish more completely on the site, thus providing one criterion for deciding which habitat would be better to introduce there. In this instance, advantage is taken of one syrphid attribute sometimes regarded as a disadvantage, namely the mobility of the adult flies.
how to maximise maintenance of the intrinsic biodiversity of each habitat, but also which habitat categories have the highest biodiversity. To investigate the relative contribution made by different habitats to maintenance of biodiversity, the only data requirements are the database and regional lists for the geographic areas to be considered. Figure 4 shows the proportions of the syrphid faunas of four different parts of the European Atlantic Zone that are associated with certain broad groupings of habitats, together with these proportions for the entire Atlantic Zone fauna. This figure is derived from Speight (1996). In this way it is possible to gain an overview of the relative benefit to be derived from maintaining different habitat types. In this example, replacement of deciduous forest by coniferous forest can be seen to lead to a net decrease in overall biodiversity in all cases, with evident implications to management of forest resources. This is a rather superficial treatment of the phenomenon and it can be further explored by examination of the microhabitat requirements and traits of the species (see Speight 1996).
3. Regional biodiversity management
3b. Identification of habitats/microhabitats supporting high concentrations of anthropophobic species A frequently-addressed issue in nature conservation is how to select the species most requiring protection. This issue is usually approached via the threat
3a. Identification of habitats with a high faunal diversity Given that the faunal biodiversity of different habitats is not the same, it is justified to consider not only
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Figure 4. Representation of syrphids associated with the major habitat categories deciduous forest, coniferous forest, wetland and open ground in different parts of the Atlantic zone of Europe, expressed as the percentage of each regional list that is associated with each habitat category. Example: column 1 shows that approximately 54% of the syrphid fauna of Central France is associate with deciduous forest habitats. AZ = Atlantic zone, general; CFR = Central France; GB = Great Britain; IRL = Ireland; NFR = North France.
status of the species. In principle, at least, the more threatened the species the higher is the priority given to its protection. A variant on this theme is to divide species into two broad groups – those which generally survive in habitats subject to intensive use by man and those which generally do not, referring to these two groups as anthropophilic species and anthropophobic species, respectively. Using the Macrohabitat categories provided in the Syrph the Net database, this can be achieved by grouping the habitats subject to intensive human use into one broad category, which can be called the ‘cultural landscape’, in contradistinction to all of the other habitats, which can be grouped into a ‘non-cultural landscape’ category. The species associated with the cultural landscape category are then the anthropophilic species and the rest are the anthropophobic species. Grouping the Irish syrphid species in this way (Speight 1999) demonstrates that most of them are anthropophobic. However, when the distribution of anthropophobic species between habitats in the non-cultural landscape category is investigated, it is clear that there is considerable variation in the proportion they represent of the total syrphid fauna of individual habitats. This relationship can be investigated further by considering the proportion of the fauna of individual microhabitats that is represented by anthropophobic species, as shown in Figure 5 (from Speight 1999). The non-cultural landscape habitats can be usefully considered as belonging to two sub-groups, namely habitats which are not used by man and, in consequence, are either left on one side or eradicated
(e.g. wetlands) and habitats which are used, becoming modified in the process by management operations (woodlands and grasslands). In the latter sub-group, highest concentrations of anthropophobic species can be shown to occur in those microhabitats that are not impinged upon by land-use management procedures. The link between microhabitat and management is not directly demonstrated in Figure 5, but may nonetheless be inferred.
Discussion The histograms presented here represent a distillation of considerable quantities of ecological information into an easily assimilated visual format. The statistical probability of deriving the results portrayed can be calculated, but that type of issue has rather less import than whether the codified biological information is itself reliable and whether the observed species listed are reliably determined. Experience to-date, gathered using the species-pool approach with the Syrph the Net data on some 20 sites scattered over Ireland, France and Switzerland, indicates that a high level of accuracy can be achieved in predicting site faunas. In general, only 5–10% of species observed on a site would not be predicted to occur there using the existing database, except in man-made systems in which unrelated elements of different habitats have been put together, where prediction breaks down. Some species originating from the terrain in the surround to a site would be expected to
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Figure 5. Anthropophobic Irish syrphid species associated with selected microsite features of deciduous forest and unimproved grassland habitats, as a percentage of the total Irish syrphid fauna of each category, A–O = forest microsite features: A = tree foliage; B = trunk cavities; C = rot-holes; D = sap runs/lesions; E = tall shrubs; F = low shrubs/bushes; G = lianas; H = tall herbs; I = low growing plants; J = within tissues of leaves and stems; K = standing timber; L = fallen timber; M = stumps; N = forest litter; O = rotten tree roots; P–Y = grassland microsite features: P = tall herbs; Q = low-growing plants; R = tussocks; S = within leaves or stems; T = in stem-bases; U = in bulbs; V = ants nests; W = with root aphids; X = cow dung; Y = litter layer.
occur in syrphid samples, since syrphids are mobile. One is then reliant upon the accuracy of the codified habitat data for detection of species that have originated off-site. Use of a regional species list for prediction, without narrowing prediction to the regionally-occurring fauna known to be associated with the habitats observed onsite, inevitably leads to gross overprediction of the site fauna. Similarly, use of the habitat-association information without a regional list would lead to gross overprediction of a site fauna. These requirements restrict the use of the species pool approach to those taxonomic groups for which habitat data have been compiled in some computerised format. The species pool approach is also more difficult to use with taxonomic groups whose species cannot be characterised at the habitat level (using this term sensu CORINE), because, for example, they respond primarily to landscape features at the microhabitat scale. The Carabidae (Coleoptera) provide a good example of this problem. Carabids have well-defined microhabitats, and it is effective use of this attribute which would seem more likely to maximise the role of carabids in environmental interpretation work. When the name of a species is linked to a system codifying biological data about that species, the name becomes much more than a simple statistic. It becomes, essentially, a rudimentary model of the species itself. When the fauna of some habitat has been codified in this
way, it may be perceived as combinations of attributes of the constituent species, rather than as simply a combination of species names. It is true that, because of the superficial level of our existing knowledge, many of the species are reduced to a series of common denominators by this process, which thus denies their dissimilarities. But it is the similarities between the species which allow generalisation and make them interchangeable units of equivalent significance, in any analysis. Which species occur then becomes largely irrelevant – what is of significance is their attributes. This has potentially major significance to the way in which such issues as site management can be addressed, enabling basic interpretation of an insect species list to be carried out by non-specialists with access to computerised information about the species and reliable regional lists. For a site manager, the information locked in a list of otherwise meaningless insect names provided by some specialist in this way becomes accessible, making the list of names useful. In today’s Europe, where local specialist entomologists are generally unavailable for site managers to quiz about the significance of species listed for their sites, this would be a big step forward. Some specialists would doubtless be outraged at such a prospect and quote unfortunate consequences resulting from non-specialist interpretation of specialist data. Such difficulties might, indeed, be anticipated. But at the moment invertebrate information is almost universally ignored in, for instance, selection
Interpretation of lists of insects and management of protected sites in Europe, because there is a general perception that both the information and the specialists to interpret it are unavailable. Databasing the information about insect species into a rudimentary expert system, such as the Syrph the Net database used in the present example, provides a shortterm solution to this problem. This account has been pinned to consideration of issues of maintaining biodiversity, because biodiversity is dominated by invertebrates and insects are, at least in freshwater and terrestrial environments, the predominant invertebrates. Action taken to maintain biodiversity on protected sites, that does not take insects into account, is a contradiction in terms. Yet there are few tools available that would allow consideration of biodiversity issues relating to entire faunas. The approach exemplified here can use all species on a list, whether the list be for a site or a nation. And the need to deal with large numbers of species provides no intrinsic problem to operation of the approach, beyond the effort required to computerise the information about the species in the first place. The larger the number of species involved, the greater the confidence that can be held in the generalisations derived, particularly when questions pertaining to entire regional faunas are to be addressed. The taxonomic group employed in the present exercise, the Syrphidae, numbers some 800 species in Europe, but it would be inappropriate to attempt to generalise from attributes of the syrphid fauna to the state of Europe’s invertebrate fauna in general. In this regard what is required is development of analogous databases for other invertebrate taxa, until a more significant fraction of Europe’s invertebrate fauna can be used. Hopefully, this text may encourage others to develop similar tools based on knowledge of the taxonomic groups in which they specialise.
References Caley, M.J. and Schluter, D. (1997) The relationship between local and regional diversity. Ecology 78, 70–80.
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Castella, E. and Speight, M.C.D. (1996) Knowledge representation using fuzzy-coded variables: an example with Syrphidae (Diptera) and the assessment of riverine wetlands. Ecological Modelling 85, 13–25. Devillers, P., Devillers-Terschuern, J. and Ledant, J.-P. (1991) Habitats of the European Community. CORINE Biotopes Manual, Data specifications, Part 2, 1–300. Office for Official publications of the European Communities, Luxembourg. IUCN (1994) IUCN Red List Categories, prepared by the IUCN Species Survival Commission, as approved by the 40th. Meeting of the IUCN Council, Gland, Switzerland, 30 November, 1994. Gland, Switzerland. Keddy, P.A. (1992) Assembly and response rules: two goals for predictive community ecology. J. Veg. Sci. 3, 157–65. P¨artel, M., Zobel, M., Zobel, K. and van der Maarel, E. (1996) The species pool and its relation to species richness: evidence from Estonian plant communities. Oikos 75, 111–17. Romau, C. (1996) Interpretation manual of European Union habitats, version EUR 15, 102 pp. European Commission, Brussels. Speight, M.C.D. (1996) Syrphidae (Diptera) of Central France. Volucella 2, 20–34. Speight, M.C.D. (1997) Invertebrate species lists as management tools: an example using databased information about Syrphidae (Diptera). Proc. Colloq. conservation, management and restoration of habitats for invertebrates: enhancing biological diversity. Environmental Encounters Series, No. 33: 74–83. Council of Europe, Strasbourg. Speight, M.C.D. (1998) Species accounts of European Syrphidae (Diptera): the Atlantic zone species (revised). Syrph the Net publications 7, 1–190. Dublin. Speight, M.C.D. (1999) Syrph the Net: A database of biological information about European Syrphidae (Diptera) and its use in relation to conservation of biodiversity. In Biodiversity: The Irish Dimension (B. Rushton, ed.), pp. 156–71. R. Ir. Acad., Dublin. Speight, M.C.D., Castella, E. and Obrdlik, P. (1998) Use of the Syrph the Net database. Syrph the Net publications, 6: 1–104, Dublin. Speight, M.C.D., Castella, E., Obrdlik, P. and Schneider, E. (1997) Are CORINE habitats invertebrate habitats? In The importance of chorology to invertebrates (H. Schreiber, ed.), pp. 193–200. Proc. 10th. Int. Colloq. EIS, Saarbrucken. Zobel, M. (1997) The relative role of species pools in determining plant species richness: an alternative explanation of species coexistence? Tree 12, 266–9. Zobel, M., van der Maarel and Dupr´e, C. (1998) Species pool: the concept, its determination and significance for community restoration. Appl. Veg. Sci. 1, 55–66.
