Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

No new packs were formed between 1998 and 1992 (Sillero-Zubiri and Gottelli 1995b)
but an apparent attempt by a subordinate female to split a pack suggested that fission could be a
mechanism for pack formation (this ended when the subordinate’s litter succumbed, probably killed
by the dominant female) (Sillero-Zubiri et al. 1996a). During this period female ascendancy to
breeding status, either by immigration or inheritance, only occurred after the death of a dominant
and so the chances of a female ever securing a breeding position were low. Five out of 10 dominant
females retained their breeding position throughout four years of observation, whereas the remainder
maintained that role until they died. Breeding openings occurred at an average of 0.12 ± 0.09
opportunities for a subordinate female per year per pack. During contests for a breeding position,
resident females appeared to have an advantage over floaters (three breeding females were replaced
by their daughters after their deaths).
In late 1991 a rabies epidemic decimated the population in Bale and resulted in the
disintegration of three out of five packs in Web, causing the sudden opening of potential breeding
opportunities (Sillero-Zubiri et al. 1996b; similar epidemics took place in 2003 and 2008, see
Randall et al. 2004 and Johnson et al. 2009). Rather than forming smaller, new breeding units,
the surviving packs maintained their social cohesion and readjusted their territorial boundaries to
occupy the habitat available (Marino 2003b). After a new epidemic in 2003, seven out of nine packs
survived, and again packs remained cohesive and territory boundaries shifted (Tallents 2007). It
took five years after the first die-off for new packs to start forming, in one case by the fission of a
large pack, and twice by the grouping of dispersing individuals, mostly from neighbouring packs.
This suggested that the establishment of a new group depends not only on the availability of highquality
habitat but also on the presence of sufficient number of helpers to defence the new territory
from the ‘expansionist’ packs that survived (Marino 2003b). The population reduction also opened
breeding vacancies to subordinate females, but social factors delaying formation of new breeding
units maintained population growth low at low densities (Marino 2003b; Marino et al. 2006).
Among Ethiopian wolves, inbreeding avoidance may be an additional adaptive advantage
of female-biased dispersal and may underlie the observed mating behaviour. Male philopatry and
the long tenure of breeding females increase the potential for incest within groups, which may be
countered in part by female dispersal (Sillero-Zubiri et al. 2004). A detailed genetic study of Ethiopian
wolves also found that although mean pairwise relatedness within packs (R = 0.39) was significantly
greater than that estimated from random assignment of individuals to packs, breeding pairs were
most often unrelated (Randall et al. 2007). This strongly suggests that female-biased dispersal also
reduces the number of incestuous matings in the population. However inbreeding is not entirely
absent in the population. Kinship analysis showed that 11 of 15 (73%) of successful matings were
between unrelated individuals (R = -0.26 to 0.22, P < 0.05). Four apparently incestuous matings
resulted in 9 of 47 (19%) pups being potentially inbred (Randall et al. 2007). Given the potential
negative consequences of inbreeding for the long-term genetic and demographic viability of the
population, inbreeding should be monitored in this population, particularly in the face of further
habitat loss and/or disease outbreaks.
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 69