Plecoptera (Linnaeus, 1758)

Fochetti, Romolo & Figueroa, José Manuel Tierno De, 2006, Notes on diversity and conservation of the European fauna of Plecoptera (Insecta), Journal of Natural History 40 (41 - 43), pp. 2361-2369 : 2362-2364

European Plecoptera diversity

A total of 426 Plecoptera species, belonging to 35 genera, have been described or listed for the European continent ( Fauna Europaea Web Service 2004) ( Table I). Thirteen genera (37% of the total) are monospecific, whereas the four most diverse ones ( Leuctra , Protonemura , Nemoura , and Isoperla ) include approximately 69% of the European stonefly species.

From a historical taxonomic perspective, Phryganea bicaudata (now Diura bicaudata ), Phryganea nebulosa (now Taeniopteryx nebulosa ), and Phryganea fusca (now Leuctra fusca ) were the first three named species of Plecoptera ( Linnaeus 1758) . Since then a first description peak occurred in the decade 1832–1842 (mainly due to Pictet), a second one extended from the last decade of the 19th century to the first decade of the 20th century (mainly due to the Plecopterists Klapálek, Kempny, and Ris), and a third period of intense taxonomic activity occurred from 1952 to the present (mainly due to authors such as Aubert, Zwick, Ravizza, Vinçon, etc.) ( Figure 1 ). In the last 25 years, a mean of 2.6 Plecoptera species per year were described in Europe. This relatively high rate of discovery of new taxa is offset by the loss of diversity due to local taxa extinctions. However, extinction is difficult to demonstrate, particularly in areas where no taxonomic or faunistic research has been carried out in the past, or where no relevant studies were conducted in recent decades (this is the case, for instance, of Belgium, studied only by Aubert in 1956 and 1957).

When describing the species distribution ( Figure 2 ), we had to consider political units (as used in the Fauna Europaea) and that made it more difficult to infer general patterns; however it appears that:

1. Very high species richness and endemism exist in Mediterranean peninsular countries (particularly Spain and Italy) mainly due to: (1) presence of mountain regions (Pyrenees, Betic system, Apennines, Italian Alps), which represent an optimal environment for stoneflies, and (2) the effect of glaciations, that favoured isolation and speciation processes (as demonstrated by the high number of endemic species). Nevertheless, species richness generally decreases in these countries from North to South ( Sánchez-Ortega and Tierno de Figueroa 1996; Fochetti et al. 1998) due to the well-known peninsular effect ( Simpson 1964).

2. Species richness is high in mountainous Central Europe countries (Alpine or Carpathic). Again, this can be explained by the preference of stoneflies for welloxygenated high mountain streams. The scarcity of endemics is a consequence of the generally small size of these countries, of the unnatural political boundaries used in analyses, and of the post-glacial recolonisation of these countries by widespread species.

3. Low species richness occurs in Northern Europe, also due to Pleistocene glaciation, even though the stonefly fauna can be unusual in some countries (e.g. the UK has an endemic species).

4. Plecoptera species are absent from the Atlantic islands (Azores, Madeira, Selvagens, Canaries) as a consequence of their distance or isolation from the continent, and the poor ability of stoneflies to disperse. Other islands (Balearic, North Aegean, Cyclades, Crete, etc.) which are closer to the continent or have been joined to continental Europe, have a stonefly fauna, even though it is often numerically reduced .

5. Plecoptera species are apparently reduced or even absent in several areas, such as the Republic of Moldova; this could be the consequence, in several cases, of lack of studies.

A detailed analysis of European Plecoptera distribution can be found in Illies (1953, 1967, 1978), Raušer (1962, 1971), and Zwick (1980, 1981).

The high number of endemic species (approximately 33% of the total, according to the political areas considered by the project Fauna Europaea) increases the risk of species disappearance. While widely distributed species can survive in more or less dispersed rifugia in case their range is fragmented, species with restricted distribution cannot. Moreover, several endemic species are still known only from the type localities and from a low number of individuals, as is the case for many species described in the last two decades. Thus, although conclusions must be carefully drawn (waiting for instance for new surveys that quantify the real population size or the real distribution area), in many cases it can be stated that species are in fact rare and potentially threatened.

Figures

Figure 1. Number (left) and cumulative number (right) of Plecoptera taxa described or cited for Europe from 1758 to present.

Figure 2. Number of species and endemic species of Plecoptera divided by countries in Europe.