Revue internationale d'écologie méditerranéenne International ...

254
◆ FAITS DE CONSERVATION EN MÉDITERRANÉE / MEDITERRANEAN CONSERVATION NEWS
The decline in rabbit numbers:
what if we change the timing of hunting?
Currently, wild rabbit populations in Spain are at their lowest
ever recorded levels. Over the last decade a number of populations
at the edge of the original distribution range have become
extinct. The main causes seem to be, firstly, changes in the landscape
in the last century and, secondly, the arrival of two diseases
(Myxomatosis in the 1950s and Rabbit Haemorrhagic Disease in
the 1990s). Subsequently, pressure from hunters and predators
have put a brake on the recovery of rabbit populations. Given
this situation of low rabbit abundance and the need to conserve
their populations, one wonders if it might not be better to hunt
rabbits at a different time of year.
We have tried to solve this question by means of a mathematical
model of rabbit population dynamics. The model is based
on data obtained from a rabbit population in southwest Spain.
We have simulated the effect of hunting at different times of year
and the effect of different degrees of hunting pressure. Mortality
rates of three age-classes (newly-born, juvenile and adult rabbits),
the proportion of reproductive females and their fecundity were
implemented with Stella software and run on a monthly time step.
Hunting is included as an additional cause of mortality and was
applied during three consecutive months of the year. We used
three juvenile survival rates (high, medium and low) to simulate
different levels of population abundance.
As expected, results from our model indicated that the current
timing of the hunting season (October to December) probably
contributes greatly to the decline in rabbit populations given that
this period happens to be the best time to control rabbit populations.
On the other hand, late spring hunting optimises hunting
success and leads to rabbit conservation. The number of rabbits
hunted is greatest when hunting is performed in late spring rather
than in autumn. In addition, since number of adults and juveniles
vary throughout the year, more adults are killed when controls
are carried out in autumn, whereas more young rabbits are killed
when controls are performed in late spring (fig. 1).
The benefits of hunting in late spring are more marked when the
population abundance is high. On the other hand, if populations are
low, hunting pressure affects rabbit populations more significantly
than the timing of the hunting period. Thus, in areas of low rabbit
abundance it is especially important for hunters to reduce hunting
pressure to encourage the recovery of rabbit populations.
Modelling leads to a simplification of real situations and thus the
results of such exercises should be analysed with care. Some important
assumptions were made to simplify the model. For example, we
assumed that hunters shoot rabbits of different ages according to the
proportion of each age group in the population, thereby ignoring a
variety of factors such as age-related differences in the detection of
rabbit by hunters and rabbit behavioural characteristics that influence
the selection of hunted animals. We are currently carrying out further
research into potential biases affecting the hunting of rabbits and their
effects on the timing of hunting.
Fore more information, read:
— ANGULO E., VILLAFUERTE R., 2003. Modelling hunting
strategies for the conservation of wild rabbit populations.
Biological Conservation, 115: 291–301.
ELENA ANGULO
UNIVERSITÉ PARIS-SUD XI
LAB. ECOLOGIE, SYSTÉM ATIQUE ET EVOLUTION (BAT-362)
F-91405 ORSAY CEDEX, FRANCE
E-MAIL ADDRESS: ELENA.ANGULO@ESE.U-PSUD.FR
GIS analyses guide the reintroduction strategy
for the Mallorcan midwife toad
In the late 1970s a small toad that was thought to be
extinct was found breeding in a remote torrent in the Serra de
Tramuntana mountains of Mallorca. Identified as the Mallorcan
midwife toad (Alytes muletensis) or ‘Ferreret’, this remarkable
discovery precipitated a wider survey and recovery programme
for the species. Toads were subsequently found to be breeding
in several limestone gorges within the mountains, but were
absent from lower-lying areas where fossil evidence suggested
they once occurred. Although loss of breeding habitat associated
with development across the island has undoubtedly contributed
to the toad’s current highly restricted distribution, introduced
predators and competitors have also impacted significantly on
toad populations. Notable among these are the amphibian-eating
viperine snake (Natrix maura) and the green frog (Rana perezi).
It appears that introduced snakes and frogs may have exterminated
the Mallorcan midwife toad from much of its former range.
Although these predators continue to impact on toad populations
in some upland areas, toads may now be confined to areas that
are sub-optimal for these aliens. A GIS analysis of the landscapes
in which toad populations occurred revealed that their breeding
pools were associated with steep surrounding slopes. Further analyses
showed that the presence of alien predators in these areas
was negatively related to altitude. Toads produced more tadpoles
in breeding pools at higher altitudes, and the productivity of the
toad populations was related to the number of breeding pools at
each site. The Mallorcan midwife toad is the subject of an ongoing
captive breeding and reintroduction programme, and these results
suggest that optimal sites for releasing toads should be high-altitude
torrent pools surrounded by steep slopes.
For more information, read:
— MOORE, R.D., GRIFFITHS, R.A. & ROMAN, A., 2004.
DISTRIB UTION OF THE MALLORCAN MIDWIFE TOAD (Alytes muletensis)
in relation to landscape topography and introduced predators.
Biological Conservation, 116: 327-332.
Richar d A. Gr if f it hs,
The Durrell, Institute for Conservation and Ecology,
University of Kent, Canterbury, Kent CT2 7NS, UK
R.A.Griffiths@kent.ac.uk
ecologia mediterranea, tome 29, fascicule 2, 2003