Continents Glaciations Bioregions What Do We Know About Their Relevance For Distribution Patterns Of Wooddecay Fungi

While the biogeography of plants and animals has been a research topic for more than a century, biogeography patterns of fungi are only beginning to emerge (Knudsen and Ryman, 2000; Hibbet, 2001). Considering the potential of fungi for long distance dispersal it would be expected that major prehistoric processes, for example continental drift and major glaciations, would have had relatively low impact on the present distribution of fungi compared to terrestrial plant and animal taxa, which generally have much lower potential for long range dispersal. Accordingly, many fungal species have traditionally been believed to have very wide if not global distribution patterns (e.g. Hallenberg, 1995). Modern molecular studies increasingly indicate that this is not the case to the extent earlier believed.

Among wood-inhabiting fungi, species previously thought to have very wide distribution in fact comprise separate taxa, each with a much more restricted distribution (e.g. Nilsson et al., 2003; Fischer and Binder, 2004; Zervakis et al., 2004). For instance, Hyphoderma setigurum has been reported from all tree bearing continents but, in fact, comprises a species complex with at least nine putatively identified taxa (Nilsson et al., 2003). Four of those investigated were restricted to northern Europe, one to Greenland, two to North America and two to East Asia. One lineage, on the other hand, was found in Greenland, North America, Caucasus and Eastern Asia. Even at the intraspecific level genetic as well as morphological and mating differentiation has been reported between regions (e.g. Petersen and Bermudes, 1992; James et al., 2001), although there are also examples of very low genetic differentiation in wood-inhabiting fungi over thousands of kilometres (e.g. Johannesson et al., 2001).

So far the true biographical distribution has been determined for very few wood-inhabiting species and it is currently difficult to evaluate how common various distribution patterns are. It is, however, evident that biogeographical patterns reported for plant and animal taxa are also relevant for fungi, such that current distribution patterns reflect major prehistoric events, for example continental drift, formation of land bridges etc. (e.g. Hibbet, 2001). In particular the distribution of major forest types seem to have a strong influence on species distribution patterns, with large and consistent differences in species composition occurring among forests dominated by, for example Pinaceae, Betulaceae, Fagaceae or Polycarps over large geographical scales (e.g. Christensen, 2006). Many species in the boreal zone thus have a circumglobal distribution, occurring in Europe, North America and possibly throughout Siberia (Hallenberg, 1995), probably reflecting the fact that the taiga zone has been coherent for many millennia. Many species occurring in the temperate deciduous forest zone in Europe are also reported in similar forest types in North America and East Asia but in most cases compatibility has not been tested between continents. The same applies to many species with a southern or Mediterranean distribution widely reported from subtropical and tropical regions, for example in East Africa and southern North America (Ryvarden and Gilbertson, 1992, 1993). On the other hand, there are also a large number of described species which are known from only very few records in geographically small areas, though they may have a wider distribution yet to be resolved.

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