Principios de Taxonomia

236j Scientific Terms
barriers prevent cross-mating between species and, hence, separate species. The
origination of prezygotic barriers between two species usually requires sympatric
coexistence of the two species.
Race Synonymous with subspecies. Races are groups of organisms at a geographic
distance from each other that have adapted to the peculiarities of their local habitats.
Different races of a species are cohesively connected to each other via gene flow in
clinal transitional zones, where they produce intermediate phenotypes. Therefore,
races exist only because they are isolated by distance. Races are distinguished from
morphs, which coexist in the same region and interbreed in an unrestricted fashion
but do not produce intermediates (see morph).
Reinforcement The origination of prezygotic mating barriers under selective
pressure between two species with a syntopic occurrence if crossings between
these species generate hybrids with reduced fertility or vitality. Reinforcement is
often observed in species that invade the territory of other species.
Relational grouping Grouping of organisms based on criteria of relational cohesion
among the organisms, for example, if the organisms are descendants of a common
ancestor or members of a sexual gene-flow community. Grouping of organisms by
relational cohesion is the opposite of class formation (Figure 2.5).
Reproductive community A species concept that implies that all organisms of a
species actually or potentially reproduce successfully with each other. In contrast, the
species concept of a gene-flow community means that all organisms that are
connected stepwise via sexual gene exchange belong to a species; geographically
distant organisms are not necessarily reproductively compatible with each other.
Allopatrically separated organisms may belong to the same reproductive community,
but never to the same gene-flow community. Organisms within a gene-flow
community that are isolated by distance belong to the same species according to
the concept of the gene-flow community, but may not necessarily belong to the same
reproductive community (see gene-flow community).
Ring species A special form of isolation by distance in which geographically
distant and genetically incompatible races of a species encounter each other after they
have spread around an inhospitable geographic region, such as a mountain range,
desert or polar region. The distribution area thus forms a ring (Figure 6.2). The
peculiarity of ring species is that the distant, incompatible races of a species meet
each other under natural conditions. In most cases of isolation by distance, the
situation is the same, but the distant races do not encounter each other.
Self-fertilization The production of offspring from a zygote that has been fertilized
by the sperm of the same parental individual that produced the egg.
Speciation, allopatric The origination of two new species under the condition that
the individuals cannot encounter each other during the process of speciation; in most
cases, this is because of geographic separation. The process of allopatric speciation is
entirely different from the process of sympatric speciation in several respects.