Testate amoebae are amoeboid protists inhabiting a test (shell).

Aim  To review and critically assess the evidence that the testate amoeba species Nebela vas does not have a cosmopolitan distribution, in contradiction to the paradigm of microbial distribution that ‘everything is everywhere’. Location  Terrestrial and wetland habitats world‐wide. Methods  Relevant data were assembled on the morphology, ecology and global geographical distribution of N. vas from a comprehensive literature review of published original records. The data were collated, analysed and summarized. The roles of long‐term and short‐term agents of dispersal are discussed. Results  A clear and repeated pattern has been elucidated of a microbial species, with a distinctive and unmistakeable morphology, that inhabits acid, damp terrestrial and wetland habitats in the southern cool‐temperate and sub‐Antarctic zones – including similar high‐altitude habitats in the Tropics. It is almost entirely confined to the Gondwanaland continents and Southern Hemisphere islands. It is definitively absent from Holarctic regions. It is proposed that the continental distribution of N. vas is a consequence of continental drift following its original speciation in the Mesozoic or earlier, whereas its distribution on sub‐Antarctic islands (glaciated in the Pleistocene) has been effected by dispersal from South America by wind around the Southern Ocean. Main conclusion  Nebela vas is a proven instance of a microbial species that does not have a cosmopolitan distribution.

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Heterotrophic protozoa have a global distribution in terrestrial habitats. The functional groups significantly represented are zooflagellates, ciliates, gymnamoebae and testate amoebae. Their range extends into the Antarctic zone, but the species richness of the communities is rarely of the same order of magnitude as those in temperate latitudes. Species diversity is usually very low owing to dominance of the communities by single, or a few, species which are best adapted to the Antarctic terrestrial environment. This is characterized by seasonal, diurnal or unpredictable fluctuations in moisture, temperature and bacterial food supply of high amplitude. The fauna shows pauperization with latitude and climatic severity. Nearly all records of species distribution are consistent with the model that community composition is determined by local conditions. An important exception is the distribution of the testate amoeba genus Nebela whose species distribution is influenced by biogeographical factors. Successional changes in community composition in fellfield habitats are characterized by the sequence: pioneer microflagellate colonizers, larger flagellates and small ciliates, and finally testate amoebae. The succession is most closely correlated with the accumulation of organic matter. A model of the strategies of dominant microflagellate species can be constructed by ordinating them on a two-dimensional habitat template of A--r-K selection continuum. The globally ubiquitous microflagellate Heteromita globosa emerges as the most strongly A-selected and K-selected. The occurrence of terrestrial protozoa near their latitudinal limits of distribution can serve as sensitive indicators of the biological effects of climatic change. Having short generation times and effective means of cyst dispersal, changes in the gross distribution can provide rapid warning of critical changes in thermal regimes.

Testate amoebae are amoeboid protists inhabiting a test (shell).