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Conservation and control strategies for the wolf (Canis lupus) in western Europe based on demographic models
Guillaume Chapron a,∗, Stéphane Legendre a, Régis Ferrière a,b, Jean Clobert c, Robert G. Haight da Laboratoire d’écologie, CNRS UMR 7625, École normale supérieure, 46, rue d’Ulm, 75230 Paris cedex 05, France
b Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA c Laboratoire d’écologie, CNRS UMR 7625, bât. A, 7e étage, université Pierre-et-Marie-Curie, case 237, 7, quai Saint-Bernard,
75252 Paris cedex 05, France d USDA Forest Service, North Central Research Station, 1992 Folwell Ave., St. Paul, MN 55108, USA
.....The unit of a wolf population is the pack, consisting
of a breeding pair and their offspring (from one
or more generations [25,26]). The dominant adult female
in each pack breeds every year, usually producing
a single litter. Subordinates rarely become dominant
in their natal pack [27]. Pups reach their adult
size by winter, and most of them disperse as yearlings
[28–30]. A dispersing wolf may colonize a vacant territory,
or it may join another pack and replace a missing
breeding member [29,31–33]. When both breeding
adults die, the pack usually disintegrates, leaving
the territory vacant and creating an opportunity
for recolonization [33].Wolves are not habitat-specific
and can live wherever they have sufficient food resources
and are tolerated by humans [7,34]. There is
no simple relationship between human density and
wolf persistence in a given area [35]. For example, in
the Abruzzi region, in Italy, wolves survive alongside
29 people/km2, whereas they have been exterminated
amongst 1.33 people/km2 in Sweden [36].
2.2. Life cycle modelling
Our models are based on the wolf life cycle described
in previous individual-based model papers
[37,38] and refined with the few available demographic
data on European wolves [12,39]. The population
is divided into several stages defined by age and
breeding status. The algorithms allow an individualbased
approach.Wolves present in packs are pups (0–
6 months), juveniles (6–18 months), subadults (18–
30 months), adults (> 30 months) and pack leaders that
are at least 18 months old. Wolves outside packs are
juveniles that have dispersed from their packs and stay
one year as lonely wolves since they are too young to
reproduce.
All our population projections involve the same
sequence of events. (i) Winter mortality affects the
whole population and accounts for annual mortality.
(ii) Dispersal of subordinates is conditional to the survival
of the breeding pair: if the breeding pair disappears
(both partners die), remaining pack members
disperse, but if at least one breeder survives, subordinates
disperse with some probability specific to their
class. (iii) Dispersing wolves search for a vacant territory
and a partner. We neglect the probability that a
dispersing wolf joins an extant pack where no breeder
is missing. (iv) Reproduction takes place in spring if
a breeding pair is present. Age at first reproduction is
always 22 months (dispersing juveniles must wait one
year before looking for a mate). Only one litter is produced
per year. (v) Pup mortality takes place in summer
and accounts for infectious diseases that are often
deadly for pups. In autumn, the distribution of wolves
in the population is censused and then updated according
to the following scheme (see also Fig. 1).
Fig. 1. Life cycle graph for a wolf stage-structured population.
P: Pups, J: Juveniles, S: Subadults, Di: Dispersers, A: Adults,
Do: Dominants. All stages are in packs except dispersers. See text
for arrow details.
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