Browsing by Author "Mariotti, Elena"

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Home range establishment of translocated African elephants (Loxodonta africana) in a savanna environment
(University of the Witwatersrand, Johannesburg, 2023-09) Ngorima, Patmore; Parrini, Francesca; Boyers, Melinda; Mariotti, Elena
Data from nine female African elephants translocated to Hurungwe Safari Area that had been collared was used to estimate home range patterns. Monthly home ranges for each elephant were estimated using the 50% and 95% Kernel Density Estimates (KDEs) method for a period of 20 months following translocation. At the population level, a linear regression model was used to test for the effect of months from release on the home range patterns. The findings revealed that the 95% home range of the elephants increased over time, while the 50% home range decreased since their initial release. I went further to compare the individual differences using the generalised additive model. The results showed some individual differences in patterns of exploration, with some displaying more linear home range patterns than others. Over and above, a considerably positive and relevant relationship between time and variation in the extent of the home range was observed.
Quantity Discriminatory Capacity and Choice Preference Between Binary Rewards in African Elephants
(University of the Witwatersrand, Johannesburg, 2024) Mariotti, Elena; Parrini, Francesca; Ross, Don
The ability to quantitatively discriminate between different numbers of the same items is shared by most animals and pre-verbal humans, and it is a requirement for being able to do simple arithmetic operations. This thesis investigated African elephants’ (Loxodonta africana) ability to do simple arithmetic by testing their quantity discrimination ability, potential drivers of it, and their learning ability, with a special focus on individual differences. The results from this thesis provide informative priors representing a necessary foundation to quantitatively estimate the risk preferences of elephants in further choice tasks, which is the aim of the larger project this thesis is part of. Individual elephants were presented with binary choices over different quantities of the same food. All data analysis used a Bayesian framework, to allow informed inferences about individual elephants. First, the preference of the elephants for different fruits was measured. Subsequently, using game pellets and the preferred fruits, quantity discrimination choices were observed using olfactory-only or olfactory-and-sound as cues. Elephants were successful in discriminating between different quantities based on olfactory cues only, but only when they could smell directly on the top of the perforated buckets containing the rewards. A combination of olfactory information and sound reduced their discrimination ability. The absolute difference between the alternatives had a stronger effect on the choices made by the elephants when the difference between the alternatives was larger, while the ratio of the alternatives affected the choices mostly when the two alternatives were similar in size, regardless of the food used. This finding suggests that elephant olfactory quantity discrimination was driven mainly by the numerosity of the rewards rather than by the idiosyncratic characteristics of the food. Grouping the quantity discrimination evidence over each reward together, I was able to show that elephants can perform simple arithmetic operations, being more precise when the alternatives differ by at least two units. The learning ability of the elephants was affected by the order and difficulty of the tasks, with initial tasks, when elephants were not accustomed to the experimental set-up yet, showing clear indication of learning. The fact that the elephants in this study were able to successfully discriminate between different quantities of different fruits, that they were relatively precise when the difference between the alternatives was at least 2 units, and that they showed signs of learning over the course of novel tasks, allows one to infer that eliciting the risk preferences of elephants might be possible. In addition to representing the first step to a quantitative elicitation of the risk preferences of elephants, this thesis proves for the first time that African elephants can do simple arithmetic and also provides vital information to increase our understanding of how elephants make decisions in the wild.
Spatial and temporal variation in Ungulate landscape use in relation to resources and constraints
(2019) Mariotti, Elena
Ungulate resource use and distribution are shaped by resources and constraints present in the environment, which are in turn modified by herbivory. Knowing the relationships between ungulates and their environment is particularly critical when managing enclosed areas, which can contain only a limited amount and variety of resources. When resources are limited and used by many species, competition can arise with the result that some species decline in number and may eventually disappear. To investigate how ungulate landscape use varies in relation to resources and constraints in an enclosed area, four ungulate species, one generalist, plains zebra, and three specialists, black and blue wildebeest, and red hartebeest, were observed foraging over one year at Telperion and Ezemvelo nature reserves, a grassland-savanna transition zone in the eastern Highveld of South Africa. Distance between the species, elevation and forage characteristics such as grass greenness, biomass, height and distribution were compared at used and available locations at feeding patch and landscape scale across the East and West sections of the reserves. Red hartebeest and black wildebeest were mainly limited to the West section of the reserves, while blue wildebeest and zebra selected areas on both sections. Large burnt areas were selected by both wildebeest species at landscape scale while being avoided at feeding patch scale, confirming the importance of investigating different spatial scales. Changes in season triggered changes in grass selection in all species. In the dry season, red hartebeest and black wildebeest switched to feeding patches offering more biomass, blue wildebeest accepted taller grass and zebra used less green feeding patches than in other seasons. In addition, results suggest the presence of interspecific competition between black and blue wildebeest at both spatial scales, and an inability for both red hartebeest and black wildebeest to use the eastern half of the study area, probably due to lack of grass of adequate quality. Therefore, this study shows how resources and constraints interact to shaping ungulate distribution and resource use, underlining the importance of considering different spatial scales, and giving important insight for management.