BORTY YEARS O F GENECOLOGY
167
usages of his own genecological units, some of which arose undoubtedly
from linguistic difficulties. Turrill (1946) observes that in aiming at “an
understanding of the Linnaean species from an ecological point of view”,
Turesson (1922b) was justified in his use of the term ecospecies, since
species “as they are realized in nature” are ecologically dFlimited. The
whole impression gained from reading Turesson’s early writings is that
he was looking upon ecospecies synthetically: as being composed of
ecologically differentiated populations, the ecotypes, forming a mosaic
throughout the distributional area. The second criterion of the biological
species of Mayr, reproductive isolation, did not become part of the
dehition of the ecospecies until 1929, when Turesson referred to the
ecospecies as “an amphimict population, the constituents of which in
nature produce vital and fertile descendants with each other giving rise
to less vital or more or less sterile descendants in nature, however, when
crossed with constituents of any other population.”
Baker (1952) has argued that whatever interpretation may be placed
upon this definition, the most appropriate application for the term
ecospecies is in reference to population systems that are isolated from
each other by both ecological and genetical barriers. Ecotypes of the
same ecospecies are, in contrast, assumed to be inter-fertile when brought
into reproductive contact by the elimination of the eco-geographical
isolation holding them apart in nature.
Leaning as it does upon a genetical criterion, this conception of the
ecospecies would at Grst sight appear to be more useful from a genecological standpoint than the seemingly more arbitrary species concept
of nomenclatural taxonomy based as it is largely upon comparative
morphology. The genetical criterion cannot, however, be readily turned
into a definitive test, since no general principles can be enunciated for
recognizing barriers to crossing : all integrades exist between failure to
interbreed due to ecological isolation and total intersterility (HeslopHarrison, 1955). This limits the usefulness of the ecospecies concept in
comparative genecology, since it cannot be assumed that the term will
always connote the same thing. Situations in different genera can only
be assessed one against the other when all the associated circumstances
- breeding systems, nature and effectiveness of isolating mechanisms
and the like - can be compared.
In the ensuing pages, the word species is used in the usual biological
manner, permitting it to take up a meaning largely from the context
(Heslop-Harrison, 1963). In general the meaning is that of “ecospecies”
in a broadly Turessonian sense; in some instances this involves a direct
conflict with nomenclatural taxonomic usage - as in the examples of
“species pairs” like Silene maritima and S. vulgaris which stand in
relation to each other much as ecotypes of one ecospecies.
167
usages of his own genecological units, some of which arose undoubtedly
from linguistic difficulties. Turrill (1946) observes that in aiming at “an
understanding of the Linnaean species from an ecological point of view”,
Turesson (1922b) was justified in his use of the term ecospecies, since
species “as they are realized in nature” are ecologically dFlimited. The
whole impression gained from reading Turesson’s early writings is that
he was looking upon ecospecies synthetically: as being composed of
ecologically differentiated populations, the ecotypes, forming a mosaic
throughout the distributional area. The second criterion of the biological
species of Mayr, reproductive isolation, did not become part of the
dehition of the ecospecies until 1929, when Turesson referred to the
ecospecies as “an amphimict population, the constituents of which in
nature produce vital and fertile descendants with each other giving rise
to less vital or more or less sterile descendants in nature, however, when
crossed with constituents of any other population.”
Baker (1952) has argued that whatever interpretation may be placed
upon this definition, the most appropriate application for the term
ecospecies is in reference to population systems that are isolated from
each other by both ecological and genetical barriers. Ecotypes of the
same ecospecies are, in contrast, assumed to be inter-fertile when brought
into reproductive contact by the elimination of the eco-geographical
isolation holding them apart in nature.
Leaning as it does upon a genetical criterion, this conception of the
ecospecies would at Grst sight appear to be more useful from a genecological standpoint than the seemingly more arbitrary species concept
of nomenclatural taxonomy based as it is largely upon comparative
morphology. The genetical criterion cannot, however, be readily turned
into a definitive test, since no general principles can be enunciated for
recognizing barriers to crossing : all integrades exist between failure to
interbreed due to ecological isolation and total intersterility (HeslopHarrison, 1955). This limits the usefulness of the ecospecies concept in
comparative genecology, since it cannot be assumed that the term will
always connote the same thing. Situations in different genera can only
be assessed one against the other when all the associated circumstances
- breeding systems, nature and effectiveness of isolating mechanisms
and the like - can be compared.
In the ensuing pages, the word species is used in the usual biological
manner, permitting it to take up a meaning largely from the context
(Heslop-Harrison, 1963). In general the meaning is that of “ecospecies”
in a broadly Turessonian sense; in some instances this involves a direct
conflict with nomenclatural taxonomic usage - as in the examples of
“species pairs” like Silene maritima and S. vulgaris which stand in
relation to each other much as ecotypes of one ecospecies.