Biology Reference
In-Depth Information
Table 12.5: Some Species Concepts or Deinitions.
a
Biological
Members of populations that actually or potentially interbreed in nature, not
according to similarity of appearance. Appearance may be helpful in identifying
species, but it does not define them.
Chromosomal
Chromosomal rearrangements result in infertile hybrids, resulting in speciation.
Chrono species
Species at different stages in the same evolving lineage that existed at different
points in time.
Ecological
Populations have distinct ecological roles but may still exchange genes.
Evolutionary
Symbionts or behavioral imprinting render populations reproductively isolated
without ecological divergence.
Incipient
Populations that are in the process of becoming a species.
Phenetic
A set of organisms that are phenotypically similar and that look different from other
sets of organisms.
Phylogenetic
The smallest set of organisms that share an ancestor and can be distinguished
from other such sets. Under this definition, a ring species is a single species that
encompasses a lot of phenotypic variation.
Recognition species
A species is a set of organisms that can recognize each other as potential mates.
Ring species
A species with a geographic distribution that forms a ring and overlaps at the ends.
Derived in part from the University of California Museum of Paleontology web page on Evolution 101 (2011).
a
Additional definitions have been proposed.
inviability could be due to the development of divergent developmental sys-
tems. Reproductive isolation may be increased if incompletely isolated popu-
lations become
sympatric
(live together in the same area) so that selection
would fix the alleles that reduce interspecific mating. The process of increasing
isolation is called reinforcement, but how often this process occurs is debated.
Likewise, the extent of
sympatric speciation
, in which reproductive isolation
occurs without geographic isolation, remains controversial, although the sym-
patric host races of the tephritid
Rhagoletis pomonella
represent a well-docu-
mented example (
Feder et al. 1988, 1997
). The biological species concept, in the
view of some, overemphasizes reproductive isolation between populations.
The
evolutionary species concept
emphasizes the continuity of popula-
tions through time. An “evolutionary species is a lineage (ancestral-descendant
sequence of populations) evolving separately from others with its own unitary
evolutionary role and tendencies” (
Simpson 1961
). This definition focuses more
on time than the biological species concept and has been criticized as being
vague and not subject to observational test (
O'Hara 1994
).
The
phylogenetic species
is, “
…
the smallest diagnosable cluster of individ-
ual organisms within which there is a parental pattern of ancestry and descent”
(
Cracraft 1983
). Critics of this concept note that the definition of diagnosabil-
ity is vague; if examined carefully, characters can be found to diagnose virtually
