27 August 2009 - Greenlandic
polar bears became smaller over the last
century according to new research from Aarhus
University. A scientific article showing
that polar bears have shrunk, possibly due
to pollution and a reduction in sea ice,
has hit BBC, ABC News and a
range of other international media. The
discovery was made by scientists from the
National Environmental Research Institute
and Department of Biological Sciences, both
Aarhus University.
If any colleagues have
wondered about the numerous boxes around
senior scientist Christian Sonne's office
in NERI containing polar bear skulls, then
here is the explanation.
Christian Sonne together
with Rune Dietz and Niels Martin Schmidt,
all NERI, and Cino Pertoldi and Volker LOeschke,
Department of Biological Sciences, have
compared polar bear skulls from the beginning
of the 20th century with corresponding skulls
from the last half of the century. The study
in 'Journal of Zoology' describes changes
in size and form that could be linked to
increased levels of pollution and a reduction
in sea ice.
The researchers used
skulls as an indicator of body size. The
skulls from the later period were between
two and nine per cent smaller than in the
earlier period.
The story has been told
in media around the globe, such as BBC,
ABC, El Mundo and as far away from Greenland
as Hondoras and Nigeria.
Contact: Senior scientist Christian Sonne,
NERI
Professor Cino Pertoldi, Department of Biological
Sciences
Craniometric characteristics
of polar bear skulls from two periods with
contrasting levels of industrial pollution
and sea ice extent. Pertoldi, C., Sonne,
C., Dietz, R., Schmidt, N.M. & Loeschke,
V. Journal of Zoology. 2009. 1-8
+ More
Juvenile hares are not
surviving their first summer
26 August 2009 - Fewer
juvenile hares reach adulthood than before
and this represents the main reason for
the decline in the hare population experienced
in Denmark over the past 50 years. This
is one of the conclusions of a new PhD thesis
from Denmark’s National Environmental Research
Institute, Aarhus University. The thesis
also proposes a method with practical application
for monitoring hare populations.
A new PhD thesis by
Trine-Lee Wincentz Jensen brings the hare
population into focus. Trine shows that
hares do not produce fewer young than would
be expected in Denmark. On average, females
produce approx. ten young each year, a figure
that falls to eight when taking into consideration
that one in five adults does not breed.
If all juveniles survived there would be
plenty of hares for hunters in the autumn,
but this is not the case. Whereas back in
the 1950s – before the population began
to decline – the current year’s recruitment
comprised 54 per cent of hare in game bags,
this is now down to 39 per cent.
A simple population model
analysing the importance of juvenile survival
for population development indicates that
the decline in the number of juveniles surviving
to the autumn is likely to be a significant
factor in the decline in the hare population.
Trine-Lee Wincentz Jensen
concludes that the causes underlying the
poor survival rate of juveniles should be
further investigated to provide more detailed
explanation but also to gain an indication
of the measures that can curb the negative
trend.
New method for monitoring
hare populations
Today game bag statistics
are used as an indirect measure of the size
of the populations, but more direct recognition
of how many hares there are, is lacking,
especially in areas where for one reason
or another hares are not hunted.
Trine-Lee Wincentz Jensen,
in collaboration with her supervisors, has
therefore adapted a point count method for
use in the Danish landscape. She concludes
that point counts along transects have great
potential as a tool within a monitoring
programme for hare, and possibly other species
too. As the hare is easy to recognise –
in any case in areas without wild rabbits
– all else being equal the method would
be a straightforward one to apply.
Numerous small populations
The thesis also presents
the results of a genetic analysis that indicates
that the Danish hare population is divided
into a range of subpopulations. It is not
surprising that water is an effective barrier
against hare dispersal, but the thesis demonstrates
that there are populations on e.g. Zealand
in which there is little or no gene flow.
This is due likely due (in part) to hare
being highly stationary, but also indicates
that hares experience cultural landscape
structure as an effective barrier, which
in turn impedes dispersal. In the long term
this can give rise to problems if effective
populations become very small.
Identifying causes for
population decline of the brown hare (Lepus
europaeus) in agricultural landscapes in
Denmark. Wincentz, T. 2009. PhD thesis.
Dept. of Wildlife Ecology and Biodiversity,
NERI. National Environmental Research Institute,
Aarhus University , Denmark and Department
of Population Biology, University of Copenhagen.
194 pp. Sammenfatning | Summary | Full report
in pdf (3700 kB)
