ИСТИНА

Some theoretical models (e.g., Finlay 2002) postulate the two different types of large-scale distribution depending on organisms’ size: unicellular taxa are not limited in their dispersal, have purely environmentally-driven distribution, low endemicity and mainly ubiquitous; while larger-sized macro-organisms are more likely to be geographically restricted and thus have “classic” biogeographies, i.e. spatially-structured distribution patterns with high levels of endemicity. The ubiquity-biogeography transition is believed to be located in the species size range 1 to 2 mm, that is the typical size of micrometazoa, including meiofauna. The “borderline state” of meiofauna is seemingly corroborated by existence of many widespread or even cosmopolitan species (“meiofauna paradox”, Giere 2009). However, geographical patterns of their diversity and composition are unclear, and the relative role of various factors in structuring these patterns is poorly known due to lack of empirical data. We studied the world-wide distribution patterns of the harpacticoid copepods, the key group of marine meiobenthos, basing on the comprehensive database (3350 species × 21 region) compiled from many sources. About 55% of harpacticoid species are regional endemics, which is comparable with endemicity level for macro-organisms. They also demonstrate rather predictable pattern in distribution, with 40% of compositional variations explained by geography (spatial distance and geographical isolation), indicating the considerable role of dispersal limitation, while only 6% - by environment (average sea surface temperature, its annual variation and salinity), and 5% - by spatially structured environmental variations. This pattern is typical for “classical biogeography” of other metazoan taxa.