The North American latitudinal gradient in species richness and geographical range of freshwater crayfish and amphipods

Article Abstract:

An analysis of biogeographical and taxonomic data from previously published works on the geographical distribution of crayfish and amphipods in North America was conducted to prove Rapoport's rule that the distribution of organisms decreases as latitude increases. Results indicate that species richness declines progressively for the two freshwater species. For crayfish, the decline was observed from 30 degrees to 60 degrees North while for amphipods, the decline was observed from 35 degrees to 75 degrees North. Several factors such as climate, geology of the area and species interaction define the latitudinal gradients which in turn influence the geographic distribution of the study organisms.

Influence, Latitude, Crayfish, Crayfishes, Amphipoda, Amphipods

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Latitudinal ranges of teleost fish in the Atlantic and Indo-Pacific oceans

Article Abstract:

Rapoport's rule formulated by Stevens is proved to describe only a local phenomenon limited to northern land masses above 40 to 50 degrees north latitudes. The latitudinal range of non-migratory tropical teleost fish in Indo-Pacific and Atlantic are greater than fish from higher latitudes. This totally contradicts Rapoport's rule of decrease in latitudinal range of fish the nearer they approach the equator. The rule does not also apply to eastern pacific mollusks, Australian fresh water fishes and Australian mammals. The Rapoport effect may be a result of sampling bias.

Behavior, Osteichthyes, Animals, Animal dispersal, Tropical fish, Tropical fishes

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Rapoport's rule: a comparative analysis between South and North American columnar cacti

Article Abstract:

The validity of Rapoport's rule, which states the existence of a positive correlation between the latitudinal extent of the geographical range of organisms and the latitude wherein said organisms are found, is examined using a species of columnar cacti growing in North and South America. This is achieved using two databases containing a total of 3,250 records. Results show that Rapaport's rule is applicable in Mexico but not in Argentina. Moreover, cacti in the North and South American regions exhibit contrasting behavior.

South America, Cactus, Cacti, Phytogeography

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