Has the Luangwa (Zambia) hippopotamus (<i>Hippopotamus amphibius</i>) population stabilized after reaching its asymptote? What are the management challenges?

Abstract

The population size of hippo (Hippopotamus amphibius Linnaeus 1758) in Luangwa valley, Zambia was earlier assessed for the period 1976-2008 and repeated 2009-2012 and found to have reached and maintained carrying capacity K of 6000 individuals over a 165 km river stretch. This study covered the period 2009-2012 and used river bank count method as in previous studies. The method involved counting individuals and taking GPS locations of hippo schools. During the period 2009-2012 the population had maintained irregular cycles oscillating above and below K of 6000 and was still within carrying capacity band of 2000 individuals. The highest population size was still 6832 hippos (rounded off to 7000) and density of 42/km reached in 1984, and the lowest was 4765 hippos (rounded off to 5000) and density of 29/km recorded in 1978. Between 1976-2008, and 2009-2012 the population still oscillated between 5000 -7000 individuals,which is symptomatic of a population that had reached its asymptote. Plot of population size for the period 1976-2012 assumed a population model which was a hybrid between less accurate regulation and stable limit cycle. The slowdown 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.

Population Structure of the Common Hippopotamus (Hippopotamus amphibius) in the Luangwa River, Zambia

“…At K recruitment rate declines and the composition of calves and sub adults in the population also declines. Similar results were obtained during the 1970-1972 culling programme where there was an under representation of younger age classes (Marshall and Sayer, 1976) which is a true reflection of the population structure, at K (Sensu Chomba et al 2013).…”

“…The hippopotamus population size in the Luangwa River was at ecological carrying capacity K of 6,000 individuals as recorded by Chomba et al (2013). At K recruitment rate declines and the composition of calves and sub adults in the population also declines.…”

Are hippos Africa's most influential megaherbivore? A review of ecosystem engineering by the semi‐aquatic common hippopotamus

“…Moreover, hippos often congregate in large numbers (Fig. 3A) (Chomba, Simpamba & Nyirenda, 2013;Dutton et al, 2018b;Fritsch, Plebani & Downs, 2022), extenuating and amplifying their individual engineering impacts. Lewison (2007) and Lewison & Pluh aček (2017).…”

“…The highest hippo population densities are known from the Luangwa River, Zambia, where up to 42 individuals per km of river have been documented (Tembo, 1987; Chomba et al ., 2013). High to moderate hippo densities have also been observed along the Great Ruaha River (26 animals km −1 ; Stears et al ., 2018), Mara River (27 animals km −1 ; Kanga et al ., 2011), Lake Edward (19 animals km −1 shoreline; Lock, 1972), and in Kruger National Park along the Sabie (18 animals km −1 ), Olifants (14 animals km −1 ), and Letaba rivers (13 animals km −1 ) (Smit et al ., 2020).…”

Does Mortality Impact Negatively on Hippopotamus (Hippopotamus amphibius) Population Size and Density in Luangwa River, Zambia? A Historic Perspective

“…The area currently holds the largest global hippopotamus population (Lewison, 2007;Chomba et al 2013) and was found suitable for this study. The study covered incidences of mortality on hippopotamus population along the 165 km stretch of the Luangwa River and the associated riverine habitat from the Chibembe pontoon (12 o 48' S, 32 o 03'E) to the Lusangazi -Luangwa confluence (13 o 24' S, 31 o 33' E).…”