Browsing by Author "Skarpe, Christina"
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Item Activity patterns of African elephants in nutrient-rich and nutrient-poor savannas(Elsevier, 2019) Mramba, Rosemary Peter; Andreassen, Harry P.; Mlingi, Valeri; Skarpe, ChristinaThe Jarman-Bell principle states that small herbivores feed on the high quality forage in nutrient-rich, eutrophic savannas, whereas large herbivores tolerate the lower quality forage in nutrient poor, dystrophic, savannas. The African elephant, Loxodonta africana, is a large herbivore occurring in both savanna types, where it meets different quality and quantity of forage and different competition from small herbivores. Activities of elephants are comparatively well studied, but little emphasis has been on contrasting time allocation on different activities in eutrophic and in dystrophic savannas. We studied elephant activities in eutrophic Serengeti and dystrophic Mikumi, in Tanzania in order to explain differences between the savannas which differ in nutrient availability and herbivore densities. The two parks had similar, mean annual precipitation. We drove along all accessible roads in our study areas, and once an individual or a group of elephants was sighted the car was stopped for observation. We used group activity scan sampling methods to record number of individuals grazing, walking, resting, browsing, interacting with other group members or vigilant in a group. We also recorded group type, group size, and habitat. The study revealed that activity patterns of elephants differed between the eutrophic and the dystrophic savanna, between females and males, and between the wet and the dry season. Grazing was a dominant activity in both sites, particularly in the wet season, when nutritious grasses were available. There was more browsing in the eutrophic Serengeti compared to the dystrophic Mikumi and in bachelor compared to family groups, probably due to differences in availability of grass and browse, and in palatability of plant material between the sites. Resting was affected by interaction effect between site and season, where proportions of individuals resting in a group was higher in Mikumi in the dry season and in Serengeti in the wet. Walking was affected by group type, where bachelor groups walked more than family groups, probably searching for estrous females, and by interaction between season and site, where elephants walked more in Serengeti in the wet season and in Mikumi in the dry. The dry season has limited forage quantity and quality and shortage of water, thus animals face a tradeoff between resting to save energy and walking to search for water and food. We conclude that, the differences recorded between the sites might be attributed to differences in quality and quantity of grazing and browsing, as well as to differences in nutritional and reproductive demands between females and males.Item Browsing and plant traits in nutrient-rich and nutrient-poor savannas inTanzania(Cambridge University Press, 2017) Mramba, Rosemary P.; Andreassen, Harry P.; Skarpe, ChristinaEnvironmental productivityisimportantindeterminingdefensiveortolerancetraitsofplants,with nutrient-rich savannas showing tolerance and nutrient-poor showing defence traits. Animals are affected differently by such traits due to differences in size, and other characters. We studied differences in browsing as a response to plant traits by elephant, giraffe and impala in Mikumi, a nutrient-poor savanna, and Serengeti, a nutrient-rich savanna, both in Tanzania, for a total of 4 mo; 2 mo at each site. Browsing time on a plant, species and height browsed were recorded. Spinesence reduced biting rate by elephant in Serengeti to 3.8 bites min−1, compared with 4.7 without spines, but had no effect on impala or giraffe. Leaf size affected biting rate by giraffe, decreasing with size in Serengeti from 19.8 bitesmin−1to 17.4 bites min−1, increasing in Mikumi, from 17.7 to 19.5 bites min−1, but did not differ in elephant and impala. Biting rate by elephant in Serengeti decreased with browsing height from 0.6 m to 4.2 m and by impala in Mikumi decreased from 0.25 m to 1.5 m, while that of giraffe in Mikumi increased with browsing height, peaking at4.2 m. The effect was comparable for elephant and impalaItem Sexual segregation in foraging giraffe(Elsevier, 2017) Mramba, Rosemary Peter; Mahenya, Obeid; Siyaya, Annetjie; Mathisen, Karen Marie; Andreassen, Harry Peter; Skarpe, ChristinaSexual segregation in giraffe is known to vary between savannas. In this study, we compared sexual segregation in giraffe in one nutrient-rich savanna, the Serengeti National Park, one nutrient-poor, Mikumi National Park, and one medium rich savanna, Arusha National Park, (from here on referred to just by name) based on effects of sexual size dimorphism and related hypotheses. Data were collected in the wet and dry seasons, by driving road transects and making visual observations of browsing giraffe. Additional data were collected from literature (plant chemistry; mammal communities). There was a noticeable difference in browsing by females and males and in browsing between the three savannas. Females browsed a higher diversity of tree species in Serengeti whereas males browsed a higher diversity in Arusha, while the diversity of species browsed in Mikumi was high and about the same in both sexes. Females selected for high concentrations of nitrogen and low concentrations of tannins and phenolics compared to males in Serengeti but selection in Mikumi was more complex. Males browsed higher in the canopy than females in all sites, but the browsing height was generally higher in Serengeti than Mikumi and Arusha. Season had an effect on the browsing height independent of sex in Mikumi, where giraffes browsed higher in the dry season compared to the wet season. Males spent more time browsing per tree compared to females in all three sites; however, browsing time in Mikumi was also affected by season, where giraffes had longer browsing bouts in the wet season compared to the dry season. We suggest that sexual differences in forage requirement and in foraging interacts with differences in tree chemistry and in competing herbivore communities between nutrient rich and nutrient poor savanna in shaping the sexual segregation.