This Diptera checklist has its primary use in faunistic research. It is the first reference point when investigating the faunistics of a particular group and gives the list of known Dutch species by their recent names, including many synonyms or misidentifications used in the literature. It also provides information about publications referring to the group.
Otherwise, the long list of names in this catalogue may seem impressive but of purely academic nature. How, one might argue, could it be used in a practical context, such as in biodiversity research, in nature conservation or even in the field?
Biodiversity
Biodiversity studies focus on the distributions of species and the species composition of regional floras and faunas. A high richness of endemic species in a regional flora and fauna is a signal to recognize the region as a biodiversity hotspot on a global scale and these hotspots deserve conservation priorities (Myers et al., 2000[refs]07050[/refs]). Checklists provide an important basis for these studies, as editors of several other lists pointed out (Chvála, 1997d[refs]01720[/refs]; Chandler, 1998a[refs]01450[/refs]). Of course, checklists like the present one can only be used in (relatively) large-scale investigations because they lack details on single species. Still, a checklist provides useful information about regional biodiversity (comparison of species numbers in groups with other regions) and general distribution of species (groups). Comparison with checklists of other countries can yield valuable information. For example, if a species occurs solely or mainly in the Netherlands, it is a candidate for becoming a target species in nature conservation (Siepel et al., 1993[refs]09960[/refs]). If one also takes older checklists into account, one can find out which species have expanded their range and how quickly they did so. The contrary, decline of a species or range reduction, can normally not be deduced from checklists while no concise system has yet been proposed to indicate how long species have not been recorded.
Nature conservation
Nature conservation uses knowledge about the ecology of species to protect them or their environment. An important question is how species that deserve protection can be selected. At the moment, most large and appealing species have already reached a reasonable level of conservation. For smaller and less appealing creatures this is not yet the case. The importance of these smaller organisms for processes in ecosystems and the necessity of their protection are beginning to be recognized. An estimated number of more than 5000 species of Diptera occur in the Netherlands and they represent a large number of ecological roles. The importance of diversity of ecological roles in ecosystem biodiversity is increasingly valued (Schulze & Mooney, 1994[refs]09770[/refs]). Constanza et al. (1997[refs]01930[/refs]) argue that ecosystem services, such as life-support systems and pollination, are critical to human life and that they depend on well functioning ecosystems.
A basic overview is necessary to find the information about large numbers of species and their possible ecological roles. That information about the Diptera can be found here in the short descriptions of the life histories and numerous references to literature. Literally, the knowledge is in the name. Each name guides to the family and information about family and species. But names have changed in the past, hiding publications with old names from anybody but the expert. Fortunately, this checklist acts as a compendium of names, enabling one to trace old names and old references.
In practice, one could think of the species lists that were compiled during numerous field inventories. Over the years, these lists become important because they express the species composition at the year of the survey. Old lists inform us about the species composition in the early 1900's, for instance. These old inventories, though often incomplete, form a historic reference in the investigation of possible shifts in species composition, e.g., as the result of climatic change (see also Ellis et al., 1999[refs]02730[/refs]) or changes in land use. The use of historic references is common practice in determining species under threat (Verheggen & Veling, 1997[refs]11360[/refs]). However, historic accounts use the names of their particular time. Using this checklist as a dictionary of names, one is able to compare the lists of old names with the present species composition.
Within the Chironomidae there one good examples. Chironomid larvae are seen as good indicators of the quality of aquatic environments. Some species are now rare or extinct in the Netherlands, but used to occur in large numbers. However, in the interpretation of decline, one must not wrongly interpret name changes as disappearances. This is quite possible since species accounts usually do not give synonyms. Kruseman (1933[refs]05260[/refs]) reviewed many species in the Chironomidae and provided data on their distribution. However, several species he listed as common are now considered to be synonymous with other species he mentioned. If one common species was synonymised with another common species, this could be interpreted as the disappearance of a common species, but only if one compares species lists without taking the synonyms into account.
In addition to their role in ecological processes, the right of existence of invertebrate species as such has been recognised as well. European nature conservation mentions a large number of invertebrate species in the Habitat Directive, the Bern convention and international red lists (Van Helsdingen, 2000[refs]03880[/refs]; Siepel et al., 2000[refs]09970[/refs]). Those in the Habitat Directive have a high conservation
status, so it is of utmost importance to know which of these species occur in a country. Checklists provide this information at the national scale, and allow focus on the relevant species within a country. For example, the mollusc Vertigo moulinsiana (Dupuy, 1849) is included in the Habitat Directive, but in the Netherlands hardly anybody knew about it, until it was found in an area where a motorway was projected and planning was stopped.
Little is known about which other Habitat Directive invertebrates occur in the Netherlands and where. Although the Habitat Directive lists do not yet include Dutch Diptera species, they might be included in the future. At that time, this book can answer two primary questions: 'Has this species been found in the Netherlands?' and 'How can I find information about where and how it lives?'
Nature development
Likewise, when nature development projects take place, there needs to be a way to evaluate the progress of these projects. Often they are aimed at floral elements or larger and appealing animals, usually vertebrates. It may be necessary that a whole new ecological equilibrium has to be reached before these target species can establish themselves. Diptera play an essential role in many parts of the ecological network. Knowledge about which species to expect or about which species used to be present in earlier times may prove to be essential. The presence or absence of species, species groups or even whole families can indicate whether a nature development project progresses in the intended direction or not.
Monitoring
To some extent, faunistics, biodiversity research, nature conservation and evaluation of the progress of nature development all rely on monitoring. Monitoring is carrying out a number of surveys of a specific region, area or terrain during a period of time to investigate changes in composition and distribution of its flora and fauna. One of the prerequisites of monitoring is a list of species that can turn up during that process. So any research that is based on monitoring as a means of gathering data has need of an up-to-date checklist and that is exactly what the present list is hoping to offer.
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