Desert Lions
Demography |
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