Species

Phylogenetic Species Concepts 245

The sort of vicariance he has in mind includes trophic replaceability,^18 but also other
ecological dimensions, including temperature races.
However, the most significant aspect of Hennig’s definition of species lies in the
temporal dimension,^19 where he notes that species are to be delimited by events of
speciation:

The limits of the species in the longitudinal section through time would consequently

be determined by two processes of speciation: the one through which it arose as an

independent reproductive community, and the other through which the descendants of

this initial population ceased to exist as a homogenous reproductive community.

Transformations of the species morphology and genetic composition within these

two events do not affect the identity of the species, because the species is defined

here as a homogenous reproductive community. In effect, Hennig is taking the bio-

species isolationist concept to its limits.^20 Species are extinguished at the next spe-

ciation event. In his earlier work in German, he was even more concise:

(^18) Op. cit., 49–50.
(^19) Op. cit., 58–60.
(^20) Hennig himself said, “the biological species concept, used by me since 1950, does not essentially
differ from that of Mayr” [Hennig 1975, 255].
Species differences
Species
Species
Phylogenetic
relationships
Individual
Individual
Individual
Tokogenetic
relationships
Sexual dimorphismPolymorphism
Cy
clomo
rphism
Semaphoront
Semaphoront
Semaphoront
ontogenetic
relationships
Me
tamorp
hosi
s

Figure 9.2 Hennig’s view of systematic relationships.

netic” relationships that represent species. (Redrawn from Hennig 1966: 31, figure 6.)