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NUMBER 89 165
18.5 --
18 -
17.5
17
'i 16.5
16
15.5
15 •-
14.5
14
52
• A
A
5 5
A x
5 ° A A
° •
o o • •
A O • •
• % •
A X
A
a »A
° * A •
54 56 58 60 62
Greatest length
5x
£
• •
64 66 68
• L. lagopus scoticus - Derbyshire
• L. lagopus scoticus - Scotland
A L. lagopus lagopus -
Scandinavia
x L. lagopus lagopus - Russia
x L. lagopus brevirostris
o Lagopus mutus millaisi-
Scotland
o Lagopus mutus (Scotland?)
A Lagopus mutus islandorum -
Iceland
D L mutus mutus - Scandinavia
0 L. mutus mutus - Russia
A L. mutus helveticus - Alps
5 La Colombiere
1 Pin Hole Cave
FIGURE 5.—ScattergTam of humerus length of Lagopus lagopus and Lagopus mutus versus proximal width.
certain species. Studies such as that on the pygmy shrew Sorex
minutus Linnaeus in northern Europe have shown that where
two ecologically similar taxa occur in sympatry their sizes will
be more divergent than when in allopatry (Malmquist, 1985).
This does not appear to affect Lagopus today, and it could not
affect the change in size seen through time because these
changes are independent of sympatry or allopatry. Lagopus lagopus
and L. mutus are presumably not ecologically similar
enough for character displacement to take place.
The most often-quoted hypothesis to account for change in
body size during the Quaternary is that of climate and, in particular,
temperature, which is the mechanism often invoked to
account for Bergmann's Rule. Many Pleistocene mammals
from glacial episodes were larger than today, and certain authors
have suggested that thermoregulation is the causal mechanism
(Davis, 1981).
Other paleontologists and biologists, however, have agreed
that this mechanism has been applied where it may not be appropriate,
and that the subject is a much more complex one
(Lister, 1992). A counterargument proposed by Guthrie
(1984, 1990) and Geist (1986) is that it is not the climate that
directly affects an animal's size but the consequences of the
length and quality of the plant growing season, which in turn
are affected by climate. The vegetational environment, called
steppe-tundra or mammoth-steppe, has been described as very
productive on the basis of the large herbivores it supported
(Guthrie, 1990). The vegetation was a mosaic of high diversity,
although predominated by grassland. It should be noted,
however, that some palynologists have disagreed with the
concept of the mammoth-steppe. They believe the vegetation
was poor, a polar desert, based on the apparently low pollen
influx at the time. The idea that the vegetational environment
was a rich steppe-tundra has recently been expanded by Lister
and Sher (1995), who have suggested that the steppe-tundra
vegetation relied on a climatic regime that has vanished. They
pointed out that detailed climatic records, such as studies of
the Greenland ice cores, have shown that the Holocene is distinct
from the late Pleistocene in having unusually stable conditions.
Pleistocene climatic instability may have allowed the
mosaic vegetation of the steppe-tundra to persist. Once this
climatic regime ceased to exist, the megafauna, which relied
so heavily on the vegetation type the climate supported,
changed along with it. Some animals became extinct, like the
giant deer Megaloceros giganteus (Blumenbach) and the
woolly rhinoceros Coelodonta antiquitatis (Blumenbach), or
locally extinct, like the lion Panthera leo Linnaeus and spotted
hyena Crocuta crocuta Erxleben (Stuart, 1991). Others
underwent a reduction in body size, such as the fox Vulpes
vulpes Linnaeus and wild boar Sus scrofa Linnaeus (Davis,
1981). It is, therefore, an attractive hypothesis that certain