The Population Dynamics of the Luangwa (Zambia) Common Hippopotamus (Hippopotamus amphibius) during the Period 1952 – 2015

The population size of hippopotamus (Hippopotamus amphibius Linnaeus 1758) in Luangwa valley, Zambia was earlier assessed for the period 1976 -2008 and repeated 2009 -2015 and found to have reached and maintained carrying capacity K of 6000 individuals over a 165 km river stretch. This study covered the period 2009-2015 and used riverbank count method as in previous studies. In 1976, a stretch of 165 km was demarcated for intensive population monitoring using the same survey methods. Results of this monitoring showed that the population recorded high densities of up to 42 hippopotami/km during the period 1976 - 2008. The method involved counting individuals and taking GPS locations of hippopotamus schools. During the period 2009 -2015 the population had maintained irregular cycles oscillating above and below K of 6000 and was still within carrying capacity band of 3000 individuals. The highest population size was 7,862 hippopotami and density of 48/km reached in 2015, and the lowest was 4501 hippopotami and density of 27/km recorded in 1978. Between 1976-2008, and 2009-2015 the population still oscillated between 5000 - 8000 individuals, which is symptomatic of a population that had reached its asymptote. Plot of population size for the period 1976-2015 assumed a population model which was a hybrid between less accurate regulation and stable limit cycle. The slow-down in population growth at K and oscillations were attributed to environmental resistance. More studies are required to identify the impact of climate change on the population size and density fluctuations to determine whether K will rise or drop.