The African elephant (Loxodonta africana) is an iconic species that is globally threatened. Of the total continental population, 37% is found in Botswana, the highest number and density of elephants in Africa. Elephant management in this country remains challenging and complex as the population estimates and trends calculated by government and independent researchers (from aerial survey data) differ and continue to be highly debated, both locally and internationally. To add more clarity and potentially resolve this ongoing debate, this study evaluates aerial survey data collected by the Botswana government from 1990 to 2012 and compares it with population demographic field data collected in 2019-2020 to assess Botswana's elephant population trend in a multimodal fashion.
I used two different methods to evaluate aerial survey count data, the log-linear regression model and the Exponential Growth Space State (EGSS) model. In addition, I used the population demographic field data to estimate the growth rate. From the results, the average annual growth rate from the linear regression and the EGSS were both 6.17%. The growth rate estimated from the population demographics field data was estimated to be 5.17%. The age structure was comprised of the six age classes with a general increase from one age structure to the next as expected with a non significant decline in age class 3 (5-10 years) likely associated with the difficulty in differentiating this age class from the bounding age classes. There were no significant differences in the sex ratio (0.49Males:0.51Females). The age structure remained the same from 2019 to 2020, suggesting no evidence that overharvesting impacted the elephant population age structure in northern Botswana. Range expansion has also been identified with the movement of the elephant population into the southern part of the country by 2012.
Analysis of count and demographic data as well as the identification of range expansion suggest that the elephant population is growing at rate close to the maximum growth rate previously identified for this species. Data do not support assertions that the population is negatively impacted through illegal offtake. Independent studies that identify Botswana's elephant population as declining have relied on comparisons that are made between data sets obtained from divergent aerial survey methodology and survey area, elements that confound such conclusions. Estimating population trends and the growth rate of an open population is complex, never-the-less, with population growth potientially derived from both birth and/or external immigation. However, demographic data collected in during this study indicate that the fucundity rate is substantial and likely a dominating driver of the positive population growth trend. Multiple measures of population growth (aerial survey and demographic assessments) also provide the opportunity for cross-validation of derived population trends. Therefore, this study recommends that the Botswana government incorporate population demographic data (i.e., age classes) into their existing monitoring protocols. Longitudinal data collection provides a critical mechanism for understanding population trends over changing environmental dynamics and should be continued. Efforts to modify or change these approaches must employ mechanisms that will account for and standardize for differences in methodology. / Master of Science / Botswana, a semi-arid country with limited surface water sources, has the highest number of African elephants (Loxodonta africana) on the African continent. This iconic species is globally threatened, and its conservation status is highly debated, making its management complex for Botswana. The population trends for the Botswana population, from the aerial surveys, are highly debated locally and internationally. Therefore, this study re-evaluated the aerial survey data from the Botswana government (1990-2012) and estimated the population growth rate, then compared the growth rate from the aerial survey trends analysis to the growth rate from the elephant population demographics data (collected in 2019 and 2020). The results from the aerial survey data from 2012 estimated a total population of 207,545 (CI = 185,774 - 229,316) with an annual average population growth rate of 6.17%, similar to the growth rate 5% estimated from population demographic field data. Range expansion of the elephant population has also been detected since 2009, with elephants now found in previously unoccupied regions of the Central Kalahari Game Reserve and associated regions in Southern Botswana. These results suggest the elephant population in Botswana is growing at a rate close to the maximum growth rate identified for this species. There is no evidence for a declining or stable population trend or indicators suggesting harvesting pressures (poaching) are suppressing elephant numbers. The study shows the utility of incorporating various population sampling methodologies into species management in Botswana.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/113340 |
| Date | 29 July 2021 |
| Creators | Barungwi, Amo Obusitswe |
| Contributors | Fish and Wildlife Conservation, Alexander, Kathleen A., Kelly, Marcella J., Frimpong, Emmanuel A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Coverage | Botswana |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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