Species richness of the Italian fauna

The conversion of the Checklist into a database (version 1.0) allowed the assessment of the number of Italian species reported in the following table (left: animal phyla; right= insect orders) :

Performing an analysis on the number of species (excluding subspecies, already discussed in Stoch, 2000), the Italian fauna includes 56213 species of invertebrates (of which 1812 species of ‘protozoans’), which make up 97.8% of the total species richness, and 1255 vertebrates (2.2%); the total number of species listed is 57468. 37303 species (approximately 65%) are insects. On the basis of these data, the species richness of the Italian fauna is one of the highest in an European country, perhaps the absolute highest (Minelli, 1996), at least for insects; this is the only taxon which allows comparisons, being well known in other countries as well.

Notwithstanding the high number of species listed in the Checklist, it seems possible that the inventory is far from complete. During the development of some projects on the distribution of Italian fauna, financially supported by the Italian Ministry of Environment, several species new to Italy or to science were added to the Checklist after its publication. A recent detailed analysis performed on the endemic species (Stoch, 2000) demonstrated that the rate of description of new endemics in Italy is still constant. The graph represented in the following graph (Steyskal’s curve) was obtained from the data assembled by the taxonomists involved in the project on the distribution of the Italian fauna co-ordinated by the Museum of Natural History of Verona. The graph represents the cumulative number of Italian invertebrates (represented by a sample of 6500 species) plotted against the year of the first citation for Italy.

Cumulative curve (Steyskal’s curve) of the number of species cited for the Italian fauna against the year of citation

The rate of increase of species richness of the Italian fauna is still high, as the steepness of the curve clearly shows. Notwithstanding the fact that the analysis is based on an incomplete data set, it should be noticed that the study taxa were selected following rigorous guidelines and may be considered representative of the best known taxonomic groups (Stoch, 2003). All taxa poorly known in Italy, like many dipteran families, are excluded from the analysis: Minelli (1996), comparing our fauna with those of other European countries, postulated that less than one half of the Italian species were known for these taxa. Their inclusion in the graph would result in a steeper curve. Moreover, this kind of curves may underestimate the total number of species; they become steeper when new taxonomists begin to work, new taxonomic criteria are used by specialists or new kinds of habitats are explored using novel sampling techniques (Stoch, 2000). Finally, the data available up to now regard terrestrial and freshwater species: the marine fauna (including some poorly known groups, like those of the meiofauna) is not included in the analysis. For this reason we suggest that the curve reported in the graph underestimates the actual rate of increase of species richness in Italy. These facts suggest that, at the present state of our knowledge, the actual number of species in Italy cannot be assessed, and will dramatically increase in a near future.