Cladistic species can be either related lines in populations located on a phylogenetic tree between two points of branching or all the terminal branches of a phylogenetic tree. In other words, according to the cladistic concept, a species is formed at the instant of speciation and disappears at the instant of the next speciation or at the instant of extinction (Ridley 1989). According to this concept, the existence of a species is completely independent of anagenetic processes – until speciation occurs in a particular related line, i.e. to branching off of a daughter species, it continues to be considered to be a single species, even though the phenotype of its members changes and develops over time. Amongst other things, cladists recognize only branching speciation – the formation of a new species by splitting of an older species into two or more daughter species – and do not recognize the existence of chronospecies and the possibility of the existence of phyletic (anagenetic) speciation – the formation of a new species through the action of anagenetic processes occurring within a single line (see XXI.1). On the other hand, as soon as a daughter species splits off from the original species, cladists consider it to be a different species from this moment, even if the phenotype does not in any way change.
- more or less1442
- not at all1146