LINEAGE-BASED SPECIES CONCEPTS To understand lineage-based
species concepts, the terms “lineage” and “population” have to
be defined at first. A lineage is defined as “an
ancestral–descendant sequence of populations” (Simpson 1961).
The term population is usually defined as a group of conspecific
organisms that occupy a more or less well-defined geographical
region and exhibit reproductive continuity from generation to
generation (Futuyma 1998). There are several variations of this
definition (Waples and Gaggiotti 2006). In any case it has to be
specified which of the individuals that co-occur in an area form
a population. In some definitions of “population” the more usual
phrases “conspecific organisms” or “individuals of the same
species” are replaced by “interbreeding individuals” (e.g., Mayr
1942, 1963; de Queiroz and Donoghue 1988). However, such a
definition of population introduces the biological species
concept through the back-door by including it into the
definition of population. This definition wa