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

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abundance and activity pattern of <strong>the</strong> rodent community in various habitats. Combined biomass of<br />

all diurnal rodents and hares in <strong>the</strong> Afroalpine grassland habitats was estimated at 24 kg/ha in Sanetti<br />

and 26 kg/ha in Web, with giant molerats c<strong>on</strong>tributing about <strong>on</strong>e third of this biomass (we assumed<br />

that an average molerat weighed 618 g (n = 11), and occurred at a biomass of 10-25 kg/ha, with<br />

patches of up to 55 kg/ha) (Sillero-Zubiri et al. 1995a, 1995b). Stark’s hares averaged 2,250 g (n =<br />

4), giving a projected biomass of 0.4-0.7 kg/ha. A more recent study by Tallents (2007) estimated<br />

lower prey biomass, with diurnal rodents represented by 9-12 kg/ha in <strong>the</strong> short pastures of <strong>the</strong> Web<br />

Valley (with a peak of 17.1 kg/ha), 4-7 kg/ha in <strong>the</strong> meadows of Sanetti and Morebawa, and <strong>the</strong><br />

uniform Helichrysum heaths of Tullu Deemtu harbouring ca. 1.5-2.5 kg/ha.<br />

Indices of giant molerat biomass for Helichrysum dwarf-scrub and Ericaceous belt were <strong>on</strong>ly<br />

1/5 and 1/150 respectively of those in Afroalpine grasslands (Sillero-Zubiri et al. 1995b). Positive<br />

correlati<strong>on</strong>s between wolf density and molerat abundance in four areas (Tullu Deemtu, Sanetti,<br />

Web and <strong>the</strong> Ericaceous belt) suggested that molerats were a vital determinant of wolf presence<br />

(Sillero-Zubiri et al. 1995b). Because <strong>the</strong>y are roughly six times <strong>the</strong> weight of any o<strong>the</strong>r rodent,<br />

hunting T. macrocephalus is likely to be c<strong>on</strong>siderably more efficient than hunting a smaller species.<br />

N<strong>on</strong>e<strong>the</strong>less, <strong>the</strong> positive correlati<strong>on</strong> between wolf abundance and an index of biomass of smaller<br />

rodents showed that <strong>the</strong> giant molerat was not <strong>the</strong> <strong>on</strong>ly determinant of wolf distributi<strong>on</strong>. The biomass<br />

index for grass rats (in kilograms per 100 transect snap-trap nights) was highest <strong>on</strong> Sanetti Plateau,<br />

followed, in order, by Web Valley, m<strong>on</strong>tane grasslands, <strong>the</strong> Ericaceous belt and Tullu Deemtu (Table<br />

1). A. blicki and L. melan<strong>on</strong>yx were <strong>the</strong> most numerous species in Afroalpine grasslands. Ethiopian<br />

wolf density, measured both from observati<strong>on</strong> and road counts, correlated positively with <strong>the</strong> total<br />

biomass index and <strong>the</strong> biomass index for diurnal species, but not for nocturnal species. Also a<br />

positive correlati<strong>on</strong> was detected between rodent burrows and wolf sign (droppings or diggings)<br />

al<strong>on</strong>g habitat assessment transects. A similar correlati<strong>on</strong> was found between wolf signs and <strong>the</strong><br />

average index of fresh giant molerat signs (Sillero-Zubiri et al. 1995a, 1995b).<br />

Large mammal densities in <strong>the</strong> Afroalpine grasslands are low and, in any case, <strong>the</strong>y might<br />

be largely unavailable to <strong>the</strong> wolves. Rodents were <strong>the</strong> most abundant, c<strong>on</strong>veniently-sized prey,<br />

and easiest to catch. Their availability was more predictable, insofar as <strong>the</strong>ir abundance was<br />

closely associated to different habitat types ((Sillero-Zubiri et al. 1995a, 1995b, Marino 2003b,<br />

Tallents 2007). The predictability of <strong>the</strong> rodent prey may be <strong>on</strong>e selective pressure favouring pack<br />

territoriality (Sillero-Zubiri 1994).<br />

<str<strong>on</strong>g>Walia</str<strong>on</strong>g>-<str<strong>on</strong>g>Special</str<strong>on</strong>g> <str<strong>on</strong>g>Editi<strong>on</strong></str<strong>on</strong>g> <strong>on</strong> <strong>the</strong> <strong>Bale</strong> <strong>Mountains</strong> 64

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