Species, Parapatry, and the Morabine Grasshoppers

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Abstract
The diagnostic and other features of the grasshoppers of the subfamily Morabinae are described, with special reference to the characteristically parapatric distributions of congeneric species and races. The concepts of allopatry, sympatry, parapatry and geographical intergradation, and of species, race, subspecies, superspecies and semispecies, are critically examined. Two categories of parapatry, ecological and hybridization parapatry, are distinguished and defined; the occurrence of hybridization parapatry in morabine and other grasshoppers and in other groups of animal is indicated. Models of speciation are discussed, with special reference to those in which hybridization parapatry is implicated. The most generally applicable model may be the alloparapatric one of Endler; events in the parapatric tension zone are described. The meanings of reproductive isolation and isolating mechanism are discussed and their bearing on the taxonomist''s problem of finding a satisfactory criterion for distinguishing between the categories species and race. A definition of reproductive isolation is proposed. This should be tested on various groups of animals to ascertain the effect it would have on the ranking of taxa currently treated as species and as races, and hence on the stability of zoological nomenclature.