African wild ass (Equus africanus) key resources overlap with livestock and population viability in the Danakil Ecosystem (Eritrea)

Abstract

The African wild ass (Equus africanus) is the world’s most endangered equid and is classified as ‘Critically Endangered’ by the IUCN Red List. This species faces a high risk of extinction in the wild. They persist in the Danakil desert which is one of the harshest climates and terrains in the world, where they share and potentially compete with livestock and local people for water and forage. An important population exists on the Messir Plateau in the Danakil desert of Eritrea. Long-term data on reproduction and survival rate of the African wild ass are limited. The population's potential viability was estimated given assumptions on fecundity, survival rates and carrying capacity. The probability of persistence at the current capacity of 18 adult females was less than 50% in the worst-case scenario. A population with a potential carrying capacity of 37 females was projected to be almost 100% persistent under all scenarios. The model results indicated that the greatest threat to population viability may be livestock impacts on the vegetation resources that limit the African wild ass population size under anticipated climate change scenarios. During the rainfall months high numbers of livestock, particularly cattle, come from the highlands and utilize the Messir Plateau daily for three to four months, depending on green forage and seasonal water availability. This may limit forage availability for African wild ass. Density, location and faecal samples of African wild ass and livestock were collected to compare the spatial and diet overlaps between the sampled herbivore species in dry vs. rainfall months. During dry months, African wild ass spatially overlapped with resident camels, domestic donkeys, goats, and sheep. During the rainfall months, African wild ass were dispersed throughout the study area, while a high number of livestock, particularly cattle, were concentrated in the northern section nearer to temporary water sources and better vegetation. The diet of the African wild ass significantly overlapped with that of domestic donkey and cattle in both dry and wet months (p<0.0000). The African wild ass nutrient (N, P) levels in the rainfall months were significantly lower than that found in domestic donkey faecal samples (p<0.05) when cattle numbers increased on Messir Plateau and African wild ass were displaced. Access and travel distance to water is critical for lactating equid females due to energetic costs and which may affect their nutrition and the survival of their foals. Drinking behaviour (frequency, timing of visits and distance travelled to water sources) of the African wild ass on Messir Plateau was recorded and compared between lactating and non-lactating females in dry vs. rainfall months. During the dry months, female African wild ass with young foals visited permanent water once a day, travelled on average 9 km and drank only at night. Non-reproductive adult females and bachelor males travelled to water every 5-10 days. During the rainfall months, there were temporary water sources on the Messir Plateau and females with young foals drank twice a day and on average travelled 3 km to water but tended to disperse up to 7 km when livestock and people arrived on the plains area. This spatial exclusion from water sources due to livestock and people presence may reduce female African wild ass ability to provide sufficient milk to their foals. This research indicates that the lower nutrient (N, P) level of the African wild ass than domestic donkey and their threatened population viability is due to high numbers of cattle spatially displacing them from needed forage and water resources. Therefore, any conservation strategies for this rare and endangered species in the Danakil desert should consider the impact of domestic herbivores, particularly cattle on the African wild ass nutrition and the critical issue of water sources