The Oligocene to the Quaternary: climate and biology - Climate Change: Biological and Human Aspects - page 147

of British Celtic people spread from central Europe during the Iron Age sometime
around or after 1200 and were then later displaced by the Anglo-Saxons. Another

idea is that the Celts were descended from those who at the end of the last glacial
first colonised north-western Europe before 10 000 years ago. What Jeremy Searle
and colleagues did was to note that common shrews ( Sorex araneus ) and water voles
( Arvicola terrestris ) from specific mitochondrial DNA (mtDNA) lineages have peri-
pheral western/northern European distributions that are strikingly similar to that of
the Celtic people. They showed that the mtDNA lineages of three other small mammal
species (bank vole Myodes glareolus , field vole Microtus agrestis and pygmy shrew
Sorex minutus ) also form a 'Celtic fringe'. They looked at animals from northern and
western areas of Britain to find out whether they have different mtDNA from their
counterparts in other parts of the British Isles. They argue that these small mammals
most reasonably colonised Britain in a two-phase process following the LGM, with
climatically driven partial replacement of the first colonists by the second colonists,
leaving the first colonists with a peripheral (Celtic-fringe-like) geographical distribu-
tion. They suggest that these natural Celtic fringes provide insight into the same phe-
nomenon in humans and support its origin in processes following the end of the LGM.
What is happening is that only those individuals with the genetic propensity to
survive and migrate with climate change migrated laterally any great distance. They
took with them only their traits, leaving behind the genetic diversity of their species
community's ancestry. (Those that stayed perhaps migrated only a short distance
vertically or into tolerable ecological niches.) Consequently, range expansion by a
species in response to climate change reduces genetic variation at the margins of the
species range. This leads to an interesting speculation. Species range expansion might
well compromise the adaptive potential of its marginal populations. Remarkably, this
prediction had not been tested up to 2008. Then, in that year, Benoit Pujol and John
Pannell from the University of Oxford showed that populations of the plant annual
mercury ( Mercurialis annua ) responded to selection on a key life-history trait less
well than populations from the species' glacial refugium. This species expanded its
range into Spain and Portugal from North Africa following glacials, and then back
again in interglacials. Their results provided direct evidence of a decline in adaptive
potential across the geographic range of a species after a shift in its distribution. The
implications of this to ecological management with global warming is that predicting
evolutionary responses to environmental change will need to account for the genetic
variability of species and the spatial dynamics of their geographic distributions 6 .
The above examples of migration and refugia are all terrestrial but this could apply
to aquatic environments too. Furthermore, the above examples using genetic analysis
tend to suggest that refugia, where species ride out times of climatic change, often
only have a minimal changing effect on species populations within the refugia. Yet, as
with climate change per se, the comings and goings from refugia can result in signi-
ficant evolution. In 2005 results of genetic, morphological (shape) and geographical
analyses by a European and South African team of researchers showed how climate

bc

6

This may not seem important because species have survived past glacial-interglacial transitions and so
could survive future global warming. However, current and forthcoming climate change is taking place
faster than any previous glacial-interglacial changes, which means that ecosystem managers may want
to consider the (controversial) option of species translocation.