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

Introduction
Worldwide, the expansion both in range and density of domestic livestock with their human owners,
along with habitat loss and modification, has multiple and complex consequences for infectious
disease transmission between wildlife and domestic hosts. From a wildlife perspective, disease
outbreaks in larger populations, or the implementation of disease control measures which alter
mortality rates in keystone species, can cause profound ecosystem perturbation. For example, the
control of rinderpest virus in its cattle reservoir around the Serengeti Ecosystem in Tanzania, and thus
removal of spillover infections in wildebeest and buffalo, has caused alterations in vegetation and
predator and prey dynamics, with substantial knock-on changes in prey and predator populations,
vegetation and fire (Mduma et al. 2001; Holdo et al. 2009)
In small or endangered populations, disease can be an important factor contributing to species
extinction and generalist pathogens with reservoirs in domestic hosts, which can infect a wide range
of species, pose the greatest threat to endangered species (Haydon et al. 2002). Examples from
Ethiopia include the multiple outbreaks and severe mortality due to rabies and canine distemper in
the endangered Ethiopian wolf in the Bale Mountains National Park (Gordon 2010, Randall et al.
2006). In the Mago National Park area, the generalist pathogen anthrax has been regularly reported,
causing mortality in at least 21 wildlife species, including more than 2000 lesser kudus (Shiferaw et
al. 2002), as well as mortality in Swayne’s hartebeest at Senkele sanctuary (Shiferaw unpub data).
Moreover, even when the effects of pathogens are sublethal or reduce reproductive rates, effects
that are common with helminth macroparasites, such effects at the individual level can interact with
other factors such as climate or food availability. Such effects may therefore still have an impact
on populations or ecosystem dynamics and thus implications for the conservation of endangered
species (McCallum et al. 1999).
The mountain nyala (Tragelaphus buxtoni) is endemic to Ethiopia and restricted to the Arsi
and Bale massifs to the east of the Rift Valley (Malcolm and Evangelista this edition). The species is
classified as endangered by IUCN, due to its small overall total population (Bale Mountains: around
3700 animals: 95% CI: 2506 – 7135, Atickem et al. 2011, with smaller populations elsewhere,
Malcolm and Evangelista this edition), combined with a decline in both range and population
size over recent decades. The Bale Mountains are the main stronghold for the species and six
subpopulations have been identified. Some 800-1500 animals primarily use the northern woodlands
and Gaysay grasslands of the National Park in grasslands whereas the other subpopulations occur
in forests also used by livestock grazing (Mamo et al. 2008, Mamo and Pinard this edition; BMNP
2010). Even in the BMNP, the mountain nyala is not free from human or livestock influence, as
encroachment into the park has regularly occurred and people, vehicles and livestock regularly
transit the Gaysay grasslands on their way to Dinsho town. Moreover, the small Gaysay grassland
(~ 40km2 ) and northern woodlands in this northern extension of the park have a ‘hard edge’ as they
are surrounded by human settlement on three sides.
Mountain nyala may thus be directly disturbed by humans and their activities and are also
at risk of disease transmission from generalist pathogens of livestock. This paper examines some
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 270