Pattern and process in the ecological biogeography of European freshwater fish

Species lists for regions of Europe defined by Illies (1978, Limnofauna Europaea, 2nd edn. Gustav Fischer Verlag, Stuttgart), and augmented by information from Maitland (2000, Guide to Freshwater Fish of Britain and Europe. Hamlyn, London), are used to describe patterns in freshwater fish species richness and to examine the contribution of habitat preference, migration, body size and glacial history to these patterns. The number of non-endemic species declines to the north and west, with increasing distance from the Ponto-Caspian region, the main source area, whereas endemic species richness declines only with latitude. Habitat generalists tend to be migratory while riverine specialists are usually resident. Similar numbers of riverine species and generalists occur in Europe as a whole but generalists dominate in regional faunas and, to an increasing extent, in more isolated, formerly glaciated areas. Very few lacustrine specialists were found, reflecting the geologically ephemeral nature of lakes. Only 8% of riverine species have colonized glaciated areas, compared with more than half the generalist species, and the number declines rapidly with increasing distance from the source area. Diadromous species show no geographical variation in species richness but potamodromous and resident species are affected by glaciation and by mountain and marine barriers. The mean body size of regional faunas increases with latitude because there are relatively fewer small species in more distant, glaciated areas. About half the species occurring in Europe are restricted to one region and the majority of these endemics occur in barrier regions with Mediterranean climates. Species in glaciated regions have much larger range sizes. Habitat preference and migration type, not body size, are the main determinants of range size. Freshwater habitat availability varies across Europe with glaciated areas having more lakes of a given size than unglaciated areas. Catchment size is greatest at mid-latitudes. For a given catchment size rivers in glaciated areas are shorter. The results support the notion that habitat variability, on both short and long time scales, favours colonization ability, which requires large body size. As a result of their limited vagility northern fish faunas are depauperate, show high levels of plasticity and polymorphism and may show elevated speciation rates. The isolated southern faunas of the Iberian and Italian peninsulas and the Balkans are rich in endemic species but may be subject to extinctions because of the spread of the highly seasonal Mediterranean climate.