biogeography

Euglenoids, as well as another algal and protistian group, have a global distribution pattern. Notwithstanding, there are several questions connected with the euglenoids’ distribution on the species level – the existence of worldwide distributed species and, on the other hand, there are theories about endemic species. With these tasks, two main distributional theories about microorganisms are connected – ubiquity theory (Finlay et al. 1996, 2004, Finlay & Fenchel 2004, Fenchel & Finlay 2004) and the theory of moderate endemism (Foissner 1999, 2006, 2007).

Finlay’s concept (Finlay et al. 1996, 2004, Finlay & Fenchel 2004, Fenchel & Finlay 2004) states that similar morphospecies of protists inhabit similar habitats and exhibit a global distribution, provided there are no geographical barriers. This theory is classically paraphrased as “everything is everywhere”. The ubiquitous distribution of microorganisms is explained by the high abundance of individuals within morphospecies, high rates of their migration and low or unknown rates of allopatric and non-allopatric speciation (Foissner, 2009). Several studies supported this theory, e.g. Finlay & Clarke (1999), Fenchel & Finlay (2004), Finlay & Fenchel (2004) and Řezáčová & Neustupa (2007). Finlay & Clarke (1999) studied species of the genus Paraphysomonas in 0.1 cm² of sediment from a freshwater pond in England; authors perhaps that all species in the chrysophyte genus Paraphysomonas are ubiquitous and supported this theory with their results when they identified 78 % of all species of this genus from studied samples. Similar results were brought by the study conducted by Řežáčová & Neustupa (2007) who studied species of chrysophyte genus Mallomonas in the alluvial plain and river Lužnice in the Czech Republic. As the result of the study, they recorded in their investigated localities about 86.5 % of species of Mallomonas previously reported in all types of freshwater biotopes in the country. The study of two localities (freshwater pond with 1278 eukaryotic species and shallow marine bay with 785 eukaryotic species) provided by Fenchel & Finlay (2004) and Finlay & Fenchel (2004) were performed in order to examine these records and establish the extent of global coverage of recorded species; results of these studies support the ubiquity theory of microscopic organisms smaller than 1 mm – these organisms occur worldwide wherever their required habitats are realised.

Foissner (Foissner 1999, 2006, 2007) goes with his theory of moderate endemism in the opposite way than Finlay’s concept – the theory simply says: “not everything is everywhere”. This theory works with the hypothesis that some species could have global distribution, but other species have limited geographical distribution. For supporting of this hypothesis, Foissner’s theory used flagship species – morphologically clearly defined and practically unchangeable species with limited geographical distribution. Tyler (1996) discussed the endemicity of algae on the examples from an Australian algal flora. He shows several taxa noted as “flagship species” – organisms which are of such a distinctive appearance or novelty that, according to Tyler (1996), there is a little doubt about their endemicity and their existence increases the probability of less-distinguished species to be also endemic. In the case of a general validity of the ubiquitous distribution of microorganisms, these species would have to be found in required habitats across the globe and due to their morphological uniqueness, clear records would have to be published about them. The theory of moderate endemicity is based on the following assumptions: the absolute abundance of individuals within morphospecies is low in the majority (≥ 90 %) of species, high only in some euryoecious species, furthermore, rates of migrations are low for most of the rare species (high only for some euryoecious species) and high rates of non-allopatric speciation (Foissner, 2009). Probably the main problem of ubiquity theory is an undersampling in several groups of microorganisms across the world – this essential knowledge gap complicates the generalized application of Finlay's theory, who discussed this problem briefly in Finlay & Fenchel (2004) for some groups of protists. Foissner uses this gap for supporting his theory of moderate endemicity and supported it with several studies, especially the study about diversity of free-living ciliates (Foissner, 1999). Results of this study show two main problems in understanding diversity and the distribution of microorganisms: (1) Foissner found an average of one new species in almost every carefully analysed sample; (2) about one-half of ciliate species (cca 1000 species) were undescribed – new for science. Additionally, Foissner (1999) claims that there are protists with a restricted geographical distribution and only a tiny fraction of the potential habitats has ever been investigated for protists – all of these results show a huge gap in distributional knowledge about protists and the problematic application of ubiquitous theory due to this gap. Simultaneously, these gaps bring problems to the moderate endemicity model too.

There are several algal groups, e.g. diatoms, silica-scaled chrysophytes and desmids – with well-studied biogeography, e.g. comprehensive studies of (e.g. Kristiansen, 1996, Foissner & Hawksworth, 2009, Fontaneto, 2011). Concerning other algal groups, there are still present some gaps and their biogeography is still a challenging task. Similarly, this is the case of euglenoids too. The first attempt to affect biogeography of euglenoids was made by Hisoriev (2001) who tried to make a comparison of local floras and made some conclusion, including the presentation of the number of endemic species (see Figure 1), and, in addition, all phytogeographical regions show quite a high number of endemic species (in the sense that they are not listed in another way than the one from compared floras). Hisoriev’s results point out the one of biogeographical problems – endemism of the microscopic organisms. Data based on literature and the exhibited high portion of endemic species should be interpreted in the other way.