This is a delightful item in which another unexpected species
response successfully to a marginal existence by adapting to a new
food supply. I do not think that the geranium is native to England
at all. However a glance at Wikipedia determines that it is
widespread, but mostly dominant in the Eastern Mediterranean. That
still suggests no lack of native cultivators so this recent
adaptation appears a bit surprising.
However, it is also possible that the little Ice Age drove them into
their refugia and that it took a fair bit of time to relearn the full
extent of its natural range. This is worth keeping in mind when
noting other expansions.
No way to prove any of this except to note the rather restrictive
'homeland' in the first place.
ScienceDaily (May 24,
2012) — A new study led by scientists in the Department of
Biology at the University of York has shown how a butterfly has
changed its diet, and consequently has sped northwards in response to
climate change.
Their study is
published in the latest issue of Science.
The researchers found
that warmer summers have allowed the Brown Argus butterfly to
complete its life cycle by eating wild Geranium plants. Because the
Geraniums are widespread in the British countryside, this change in
diet has allowed the butterfly to expand its range in Britain at a
surprisingly rapid rate. Over the past 20 years, the Brown Argus has
spread northwards by around 79 kilometres and has become common in
the countryside in much of southern England.
Lead author PhD
student Rachel Pateman, of the University of York's Department of
Biology and the NERC Centre for Ecology & Hydrology, said: "Many
species are shifting their distributions northwards as the climate
warms, but this previously scarce species has surprised everyone by
moving its range at over twice the average rate."
Co-author Chris
Thomas, Professor of Conservation Biology at York, said: "Because
wild Geraniums are widespread in the landscape, the butterflies can
now move from one patch of host plants to next and hence move rapidly
through the landscape -- expanding their range generation after
generation."
Co-author David Roy,
from the NERC Centre for Ecology & Hydrology, said: "The
change in diet represents a change to the interactions between
species -- in this case between a butterfly and the plants that its
caterpillars eat -- caused by climate warming. Changes to the
interactions between species are often predicted to alter the rate at
which species shift their distribution in response to climate change;
and now we have demonstrated this in nature."
In the 1980s the
butterfly was considered scarce in Britain, with populations
undergoing continued decline but it has subsequently undergone a
dramatic reversal of fortune. The team put this down to the effect of
climate on the ability of the butterfly to use additional food plant
species.
In the 1980s, the
caterpillars were mainly confined to Rockrose plants growing on the
chalk hills of southern England, but the use of plant species in the
Geranium family has increased as summer temperatures have increased.
Wild Geraniums are suitable food plants for the caterpillars in warm
years, but not in colder summers. This seems to be because the plants
grow in different places, which provide different microclimates.
Common Rockrose is found mainly on hot south-facing slopes, where the
butterfly can complete its life cycle even in cool summers. This is
not the case for the Geraniums and so they only become suitable for
the butterfly when summers are warm.
Co-author Richard Fox,
from the charity Butterfly Conservation, said: "It is important
that we understand how and why species are responding to climate
change. Such research would not be possible without the thousands of
records of butterflies our dedicated volunteers have collected over
many decades, which have allowed us to detect these long term
changes."
Rachel Pateman said:
"This study has highlighted that species do not respond to
climate change in isolation, and that climate change affects how
species interact with one another. In the case of the Brown Argus
butterfly, changes in interactions with its food plants have helped
it to respond to climate change very rapidly. However, changes to
interactions may hinder other species, potentially putting them at
risk of extinction."
Co-author Professor
Jane Hill, of the Department of Biology at the University of York,
said: "There will be winners and losers from climate change. It
is important that we begin to understand how the complex interactions
between species affect their ability to adapt to climate change so we
can identify those that might be at risk and where to focus
conservation efforts."
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