دانلود رایگان مقاله نتایج خشکسالی طولانی مدت در گرسنگی فیل آفریقایی

Abstract

Elephant inhabiting arid and semi-arid savannas often experience periods of drought, which, if prolonged, may cause mortality. During dry periods, elephant aggregate around water sources and deplete local forage availability. However, the relationships between adult elephant mortality and both high local elephant density and forage availability close to water during dry periods remain unexplored. We hypothesized that elephant mortality is higher: a) when dry periods are longer, b) closer to water points, and c) in areas with higher local elephant density. Using nine years of elephant carcass data from Tsavo Conservation Area in Kenya, we analysed the probability of adult elephant mortality using maximum entropy modelling (MaxEnt). We found that elephant carcasses were aggregated and elephant mortality was negatively correlated with four months cumulative precipitation prior to death (which contributed 41% to the model), Normalised Difference Vegetation Index (NDVI) (19%) and distance to water (6%), while local elephant density (19%) showed a positive correlation. Three seasons (long dry, short dry and short wet seasons) showed high probability of elephant mortality, whereas low probability was found during long wet seasons. Our results strongly suggest that elephants starve to death in prolonged drought. Artificial water holes may lead to lower mortality, but also to larger populations with subsequent high browsing pressure on the vegetation. Our results suggest that elephant populations in arid and semi-arid savannas appear to be regulated by drought-induced mortalities, which may be the best way of controlling elephant numbers without having to cull.

4. Discussion

Elephants are bulk feeders and require large amount of food to survive (Barnes, 1983; Jachmann and Bell, 1985; Jachmann, 1989; Osborn, 2004). They are also water dependent and must drink water frequently; mostly every two days (De Knegt et al., 2011; Skarpe et al., 2014). In arid and semi-arid savannas where both water and forage are deficient in the dry season, elephant are faced with two major challenges: starvation or dehydration. The results of this study show that elephant mortality was high during long drought periods, i.e., at least four consecutive months with low or no rainfall (b150 mm). Moreover, elephant carcasses were aggregated and elephant mortality was high in areas with high local elephant density, low NDVI and in close proximity to permanent rivers. With the predicted increasing frequency of droughts in (East) Africa (Collier et al., 2008; Yang et al., 2014), these findings are vital for effective conservation of the African elephant.