Desert Lions

History

Demography

Habitat

Socio-ecology

Behaviour

Dispersal

Demography & population dynamics

Lion density & population size
Population growth
Age and sex structure
Fecundity and mortality

Lion &population size
Since November 1999 a total of 40 lions were radio collared and 86 lions were marked or were individually identifiable (Table 2). Population density was calculated in two intensive study areas where all lions were marked or individually known (see Stander 2004, 2006). Using the Kunene Sampling Method (Loveridge et al. 2001) lion densities were calculated at 0.05 – 0.1 lion/100 sqr km for the low-density area and 0.38 - 0.62 lion/100 sqr km for the high-density area. The density estimates were then extrapolated to the current calculated areas of low and high density (Figure 10). The population estimates of 9 – 19 lions for the low density area, and 87 – 135 lions in the high density area, coincides with the records of known individual lions, and provides confidence to the total estimate of 96 - 154 lions in the Kunene Region.

Table 2. Density & population estimates of the Kunene lions.

Figure 10. The density distribution of lions in the Kunene Region - 2007

Population growth
In 1999/2000, when the Kunene lions were restricted in their distribution to the central Palmwag Concession area, a core group of 13 lions were marked with radio collars. The life history of these individual lions has subsequently been documented, and forms the bases of assessing population growth and expansion. The population has shown a positive growth rate between 1999 and 2006 (Figure 11). The Log exponential rate of annual growth was high initially (1999 – 2002), but leveled off somewhat thereafter. During the first two years (1999 & 2000) the population increased at a phenomenal rate 22% and 23% per year respectively, expressed by a logarithmic rate of increase (Figure 12). Between 2001 and 2004 the rate of increase remained high (15% p.a.), but dropped to below 5% p.a. in 2005, and increased again to almost 15 % by the end of 2006.

Figure 11. Growth rate of the Kunene lion population between 1999 and 2006


Figure 12. Exponential annual rate of increase of the Kunene lion population between 1999 and 2006

Age and sex structure
Despite high fecundity and growth there were discrepancies in the age structure of the population during some years (e.g. 2004 - a preponderance of sub-adult and adult lions). However, the composition of age classes is expected to vary, and the annual data, between 2000 and 2006, clearly show this fluctuation (Figure 13). These results may demonstrate the population’s ability to self-regulate, but notwithstanding, depicts the characteristics of a healthy and stable population.

Figure 13. Distribution of age classes if the Kunene lion population between 2000 and 2006.
(Small cub <1 yr; Large cub 1-2 yrs; Sub-adults 2-4 yrs; Adult 4-10 yrs; Past prime >10 yrs).


Fecundity and mortality
Mortality in the lion population was recorded in all three age-classes (N = 40; Figure 14). Human Lion Conflict was the main cause of mortality (53 %) as adult and sub-adult lions (mainly males) were either shot by local people, or trophy hunted. Cubs died mainly from starvation. Life tables of individual lions were used to calculate mortality rates (Figure 15) and survivorship (Figure 16) at different ages. The probability of survivorship (Figure 16) is highest at birth (P = 1), and then drops progressively over time, so that the older a lion becomes the lower its probability of survivorship. Mortality rate (Figure 15) is a measure of the probability of a lion dying at any specific age. Low cub mortality in the Kunene resulted in a slight reduction of survivorship in the fist year. Interestingly, survival of Kunene lions between 1 and 4 years is high. Elsewhere in Africa, lions at that age are at risk and mortalities are high. For a Kunene lion the risk of dying is highest at three to four years (Figure 15), and as a result, the probability of survivorship is reduced sharply to approximately 50%. These mortalities are all related to Human Lion Conflict. Once lions overcame the critical period, between 3 and 6 years, when they may have acquired the skills to avoid conflict with humans, mortality rates drop to P < 0.1. The probability of survivorship then remains stable up to the age of sixteen years, when the mortality rate soars. The low sample size at this age may introduce bias.

Figure 14. Causes of mortality in each age class of the Kunene lion population, between 2000 and 2006.


Figure 15. Age-specific probability of mortality rates in the Kunene population (2007).

Figure 16. Age-specific probability of survivorship in the Kunene population (2007).

Last data analysis & update - March 2007