penetrate equatorial species, peripheral, transient and distant neritic 

 species. The expatriated species have considerable significance in the 

 structure of the communities. In terms of the number of species as a 

 whole for the euphausiids, chaetognaths and foramini fers , in the north 

 central community of the Pacific Ocean, their number is about as great 

 as the number of specific species, and in the equatorial community, they 

 are even 50% more numerous. This indicates the interdependence of 

 neighbouring tropical communities (Heinrich, 1975a). 



In tropical ocean communities, the greatest numbers are, as a rule, 

 achieved by the wide-spread tropical species and specific species. 

 Expatriated species are not numerous. 



Changes in the number of widespread species. Some questions 

 arise: Just what is the large-scale pattern of distribution of the 

 number of widespread tropical species? Is it similar in different 

 species? Is there similarity between the distribution of areas of 

 abundance of widespread tropical species and ranges of species with 

 relatively narrower areas of distribution, equatorial, central, and 

 distant neritic species? What are the small-scale changes in populations 

 of wide-spread tropical species, and what factors cause them? 



Work in the Pacific and Indian Oceans on the distribution of the 

 chaetognaths, euphausiids, copepods, Siphonofora, mollusks (Bieri, 1959; 

 Brinton, 1962; Heinrich, 1960, 1968; Vinogradov, Voronina, 1962, 1963; 

 Chiba, Hirakawa, 1972; Musaeva, 1973; Gueredrat, 1974; Sakthivel, 1973) 

 have shown that the abundance of the widespread tropical species changes 

 significantly from one region to another, and that their distribution 

 is different. If we analyze the large-scale patterns of distribution of 

 population, we can distinguish four main types of distribution: 1) maxi- 

 mum abundance in equatorial waters; 2) maximum abundance in central 

 waters; 3) difference between abundance in equatorial and central regions 

 slight or zero; 4) maximum abundance in one of the distant neritic regions 



Each type has variants, and there are transitions between types. 

 Each type of distribution includes species of all trophic levels. The 

 basic large-scale regularities of horizontal distribution of abundance 

 of animals are retained throughout all seasons, and from year to year 

 (Heinrich, 1968. 1973; Chiba, Hirakawa, 1972; Gueredrat, 1974). 



The large-scale pattern of distribution of species of various 

 types can be reduced to the statement that areas of great abundance of 

 some widespread tropical species are located approximately within the 

 regions inhabited by most of the central species, of others--where most 

 of the equatorial oceanic or distant neritic species live. In neighboring 

 regions, over great areas the abundance is small, though there are some 

 small, apparently unstable, spots of higher density. 



In the western Pacific, areas have been distinguished for copepoda 

 with each type of distribution, in which most of these species have 

 maximal abundance. These areas diverge spatially quite clearly for the 

 species with the maximum abundance in the equatorial and central regions, 



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