FORTY YEARS O F GENECOLOGY
185
three colonies were sampled, and the samples were compared in standard and varied environments. Substantial differences were observed in
morphological and physiological features under standard cultivation.
The differences are considered by Bradshaw to be adaptive, and he
concludes that it is “the environment, even its local variations, which
determines the pattern of differentiation. So where there are sharp
changes in environment, . . there are sharp correlated changes in the
populations. Where there are gradual changes in the environment. . .
the population changes are equally graded. Where in such gradients
there are sudden local variations. . . there are sudden population
changes”. Evidently A. tenuis shows a mixture of continuous and discontinuous variation on a very local scale, and Bradshaw declines to
identify any of the populations as ecotypes, or even to apply the concept
of clines.
The picture sketched by Gregor and Watson (1 954) for variation in
Lolium perenne in Britain shows some similarity with that described for
Agrostis tenuis by Bradshaw. In their later investigation of local genecological variation in Plantqo lanceolata (Gregor and Watson, 1961),
sample size was restricted in favour of number of populations sampled,
in sites scattered throughout a mosaic of different habitats mainly
within an area of 70 x 30 miles in southern Scotland. The sites were
grouped into three broad classes: A, species-rich pasture; B, speciespoor, lightly grazed vegetation, and C, ungrazed vegetation dominated
by Molinia caeruleu. In cultivation under standard conditions, the plantain samples showed average leaf lengths increasing progressively from
habitat type A to habitat type C, the differences between the groups
being statistically significant. There is thus a “dispersed” ecocline in the
characteristic, in so far as the three habitat types, A, B and C, can be
regarded“as forming an ecological gradient in this small geographical
area. This study also included an assessment of the role of developmental
plasticity in the adaptation of the plantains to minor variations between the habitats.
A study of small-scale genecological differentiation by Harberd
(196lb) is of particular interest since no fewer than thirteen taxa were
investigated simultaneously. The sampling was carried out within one
broadly defined type of community, Agrostis-Festuca grassland, and
within a comparatively small geographical area. A total of eighty sites
were selected in a series ranging from “flushed” to “leached”, and five
circular turves c. 7 ern in diameter were taken from each; the plants
were grown on from ramets present in the turves. One to ten characteristics were scored in the different species. Using the within-site variance as the error term, an analysis of variance showed that more than
70% of the characters scored differed significantly between the popula-
185
three colonies were sampled, and the samples were compared in standard and varied environments. Substantial differences were observed in
morphological and physiological features under standard cultivation.
The differences are considered by Bradshaw to be adaptive, and he
concludes that it is “the environment, even its local variations, which
determines the pattern of differentiation. So where there are sharp
changes in environment, . . there are sharp correlated changes in the
populations. Where there are gradual changes in the environment. . .
the population changes are equally graded. Where in such gradients
there are sudden local variations. . . there are sudden population
changes”. Evidently A. tenuis shows a mixture of continuous and discontinuous variation on a very local scale, and Bradshaw declines to
identify any of the populations as ecotypes, or even to apply the concept
of clines.
The picture sketched by Gregor and Watson (1 954) for variation in
Lolium perenne in Britain shows some similarity with that described for
Agrostis tenuis by Bradshaw. In their later investigation of local genecological variation in Plantqo lanceolata (Gregor and Watson, 1961),
sample size was restricted in favour of number of populations sampled,
in sites scattered throughout a mosaic of different habitats mainly
within an area of 70 x 30 miles in southern Scotland. The sites were
grouped into three broad classes: A, species-rich pasture; B, speciespoor, lightly grazed vegetation, and C, ungrazed vegetation dominated
by Molinia caeruleu. In cultivation under standard conditions, the plantain samples showed average leaf lengths increasing progressively from
habitat type A to habitat type C, the differences between the groups
being statistically significant. There is thus a “dispersed” ecocline in the
characteristic, in so far as the three habitat types, A, B and C, can be
regarded“as forming an ecological gradient in this small geographical
area. This study also included an assessment of the role of developmental
plasticity in the adaptation of the plantains to minor variations between the habitats.
A study of small-scale genecological differentiation by Harberd
(196lb) is of particular interest since no fewer than thirteen taxa were
investigated simultaneously. The sampling was carried out within one
broadly defined type of community, Agrostis-Festuca grassland, and
within a comparatively small geographical area. A total of eighty sites
were selected in a series ranging from “flushed” to “leached”, and five
circular turves c. 7 ern in diameter were taken from each; the plants
were grown on from ramets present in the turves. One to ten characteristics were scored in the different species. Using the within-site variance as the error term, an analysis of variance showed that more than
70% of the characters scored differed significantly between the popula-