Population dynamics of Walia ibex (Capra walie) at Simien Mountains National Park, Ethiopia Kefyalew Alemayehu1* , Tadelle Dessie2, Solomon Gizaw3, Aynalem Haile2 and Yoseph Mekasha1 1 School of Animal and Range Sciences, Haramaya University, PO Box 138, Dire Dawa, Ethiopia, 2International Livestock Research Institute (ILRI), PO Box 5689, Addis Ababa, Ethiopia and 3Ethiopian Institutes of Agricultural Research, Debre Birhan Research Center, PO Box 112, Debre Birhan, Ethiopia Abstract Intensive total direct counts of Walia ibex (Capra walie) population were performed at Simien Mountains National Park (SMNP) in 2009. Historical data were collected from SMNP and literature reviews. Different models were suited to determine population growth rates and intrinsic rate of increase. The population size estimated was 745 animals. The correlation between the two repeated counts was significant (r = 0.99 and P < 0.01). Mean instantaneous growth rate (r), growth rate per capita (k) and population annual growth rate (K) were 2.6 ± 2.6, 0.03 ± 0.18 and 19.5 ± 50.4, respectively. Instantaneous growth rate and growth rate per capita were positively correlated (r = 0.958, P < 0.01). Average growth rate (rK) and intrinsic rate of increase (rr) under ideal (r = 0.950, P < 0.01) and random environments (r = 0.810, P < 0.01) were positively correlated. The population grows by 2.5% under ideal environments with an intrinsic increase of 0.04 (0.006%) and by 0.13% under random environments with intrinsic rate of decrease of )0.184 or )0.025% per year, respectively. The mean rank of the flock structure of whole population was 3.13, 3.88, 2.00 and 1.00 for males, females, juveniles and unidentified, respectively. National des Simien Mountains (SMNP) en 2009. Les données antérieures ont été collectées au SMNP lui-même et dans la littérature. Différents modèles furent adaptés pour déterminer le taux de croissance de la population et le taux d’accroissement intrinsèque. La taille de la population fut estimée à 745 individus. La corrélation entre les deux comptages répétés fut significative (r = 0.99; P < 0.01). Le taux de croissance instantané moyen (r), le taux de croissance par tête (k) et le taux de croissance annuel de la population (K) étaient respectivement de 2.6 ± 2.6; 0.03 ± 0.18; et 19.5 ± 50.4. Le taux de croissance instantané et le taux de croissance par tête étaient positivement liés (r = 0.958, P < 0.01). Le taux de croissance moyen (rK) et le taux d’accroissement intrinsèque (rr) dans des environnements idéaux (rK = 0.950, P < 0.01) et pris au hasard (rr = 0.810, P < 0.01) étaient positivement liés. La population s’accroı̂t de 2.5% dans un environnement idéal avec un accroissement intrinsèque de 0.04 (0.006%), et de 0.13% dans des environnements au hasard, avec un taux de croissance intrinsèque de 0.184 ou 0.025% respectivement par an. Le rang moyen de la structure des sexes de toute la population était 3.13, 3.88, 2.00, 1.00 respectivement pour les mâles, les femelles, les juvéniles et les individus de sexe non identifié. Key words: age structure, growth rates, home ranges, sex structure Introduction Résumé Des comptages directs intensifs de la population de bouquetins d’Abyssinie Capra walie furent menés dans le Parc *Correspondence: E-mail: kefyale@gmail.com Present address: Department of Animal Production and Technology, Bahir Dar University, PO Box 21 45, Bahir Dar, Ethiopia. 292 Population growth rate is the central unifying concept of population dynamics (Sibly & Hone, 2002; Lewontin, 2003). It links together all aspects of density and resource dependence, inter- and intraspecific interactions like competition, predation, mutualism, cannibalism and cooperation (Sibly & Hone, 2002). The population dynamics of wild animals oscillate because of the fluctuation of growth  2011 Blackwell Publishing Ltd, Afr. J. Ecol., 49, 292–300 Population dynamics of Walia ibex rates. This is caused by habitat disturbance and fragmentation (Diamond, Bishop & Van Balen, 1987; Birhanu, 2005), variation in age distribution (Andrew et al., 2004), disease transmitted from livestock (Pe’rez et al., 2002) and variation in the environment, which causes the rates of birth and death in the population to vary from year to year (Giardina, Philippe & M¢ezard, 2002). Long-term studies of population dynamics are of great interest in population ecology, wildlife management and conservation biology (Tuljapurkar & Caswell, 1997; Gaillard, Marco & Nigel, 1998). The factors that explain fluctuations in population size or growth rates are central theme in ecology (Tuljapurkar & Caswell, 1997). The endangered Walia ibex (Capra walie) is the most distributed ungulates of the genus Capra found in the Simien Mountains National Park (SMNP). C. walie occupies a narrow habitat niche and is vulnerable to human disturbances such as habitat loss, illegal hunting, disease and competition from livestock (Nievergelt, 1981; Gebremedhin et al., 2009). Studies performed by Paetkau et al. (1998) on North American Brown Bears, Flagstad et al. (2000) on Ethiopian Swayne’s Hartebeest and Gebremedhin et al. (2009) on C. walie indicated that environmental changes, small population size and demographic stochasticity, risk of inbreeding and loss of genetic diversity are the main threats of endangered species. The population size of C. walie oscillates since 1968 where the census data started to be considered in this paper. Understanding of the population dynamics of C. walie would therefore help to know the average growth rates and intrinsic rates of increase under ideal and random environments, and the population structure, which help us to cram the status of the population. Therefore, the objectives of this paper are to determine the population dynamics and its related parameters of Walia ibex (C. walie). Materials and methods Study site The study was conducted at a wildlife conservation area, SMNP. The park harbours two of the world’s most threatened mammals: the Walia ibex (C. walie) and the Ethiopian wolf (Canis simensis). SMNP is located in the northern parts of Ethiopia, North Gondar Zone of the Amhara National Regional State (ANRS). The geographic location extends from 139¢57¢¢ to 1319¢58¢¢ north latitude and  2011 Blackwell Publishing Ltd, Afr. J. Ecol., 49, 292–300 293 from 3754¢48¢¢ to 3824¢43¢¢ east longitude. The park is situated within three districts of North Gondar Administrative Zone, namely Debark, Janamora and Adarkay. It is 120 km north-east of Gondar, which is about 741 km away from Addis Ababa. The park has altitudes ranging from 1900 to 4543 (m.a.s.l.). It covers an area of 179 km2 of the Simien Mountains watershed (Gebremedhin et al., 2009). Methods of data collection Population census Simultaneous and intensive direct total count was made in May and November 2009 to estimate the population size of C. walie as adopted by Sale & Berkmuller (1988); Caughley & Sinclair (1994); Sutherland (1996) and Wilson et al. (1996) for different animals elsewhere in the world. Direct total counts were employed by dividing the entire habitat of C. walie into eight main census areas. These census areas are naturally occurring home ranges of C. walie delineated by gorges and mountains, namely, Buait ras, Sankaber, Ginch, Chenek, Sebatminch, Adarmaz, Muchila and Dirni. Burnham, Anderson & Lake (1980) and Smart, Ward & White (2004) suggested total count method as the most direct way to estimate the abundance of biological population. The census was conducted when C. walie is active, 07.30 to 11.00 in the morning and 16.00 to 18.30 in late afternoon. The total counts were performed with the aid of binocular telescope and ⁄ or with unaided eyes while travelling on foot. The geographic locations of each C. walie population in each study sites were identified from the ground by the help of topographic maps. Repeated counting of the individuals was avoided by using easily recognizable features like body conditions, group composition and distinct individual features such as malformed horns of ibex individuals as used in the study by Yoaciel (1981) and Birhanu (2005). Historical data of C. walie were obtained from SMNP and literature reviews such as Shackleton (1997) and Gebremedhin (1997). Population size and structure estimation Population structures (age and sex structure) of C. walie were observed during counting. Each individual sex and age classes was identified and categorized following Hillman (1986); Dahiye (1999); Refera & Bekele (2004) and Birhanu (2005) for categorizing different animals. The 294 Kefyalew Alemayehu et al. classifications of C. walie on age and sex were also employed following the classification of Nievergelt (1981). For effective population size and its contribution in breeding, minimum prime-ages (2 years) were taken into account following Gaillard, Marco & Nigel (1998). Accordingly, male and female individuals of C. walie were categorized into the following age classes: males aged between 2 and 7 years in one class while males older than 7 years in another class. On the other hand, females aged between 2 and 7 years in one class while females older than 7 years in another class. Those individual C. walie that were below 2 years were categorized as juvenile, and those that were difficult to identify their sex were categorized as unknown. Models in estimating growth rates To suppress the effect of variable census errors on the count totals and the annual estimates of the population, the original count totals were transformed using a twopoint weighted interpolation (Norman, Darryl & Ogutu, 2005) as: N = 0Æ67Nt + 0Æ33Nt + 1, where N = adjusted population estimate and Nt = recorded population count, for year t. The annual instantaneous population growth rate (r) was estimated as r = ln (Nt + 1 ⁄ Nt) (Caughley, 1977). Growth rate per capita (k) and the intrinsic rate of natural increase (K) were estimated as k = dN ⁄ dt · (1 ⁄ N) and K = rN = dN ⁄ dt, respectively (Dennis, Munholland & Scott, 1991; Morris et al., 1999; Colin, Townsend & John, 2003; Andrew et al., 2004). Population growth rate (kr) related to generation time (g) and the concept of the intrinsic rate of increase (rr) under random environment was described by the model rr = g)1 = loge (Nt + T ⁄ Nt) = loge (k). Average growth rate between consecutive observations under random environments were obtained from the standard formulae (kr) = loge (Nt + T ⁄ Nt ⁄ T) and k = er (McCullagh & Nelder, 1989). Where Nt and Nt + T are consequent observations of a species in the dataset (but not necessarily, subsequent sampling dates) and T is the time lag in years between consequent observations ⁄ censuses and k is average growth rate, r is the instantaneous population growth rate. When value of k is >1, it indicates that the population increases in size, when k is lower than 1 the population declines, and when k = 1, the population is stable. Results Population size of C. walie The average total population size estimated from the two repeated total counts was 745. The correlation between the two repeated counts were significant (r = 0. 99 and P < 0.01). The population is distributed in eight home ranges, which are delineated, by gorges and mountains, namely, Buait ras, Sankaber, Ginch, Chenek, Sebatminch, Adarmaz, Muchila and Dirni. It was densely populated on Cheneck and Sebatminch home ranges. Growth rate estimates The mean instantaneous growth rate (r), growth rate per capita (k) and population annual growth rates (K) were 2.6 ± 2.6, 0.03 ± 0.18 and 19.5 ± 50.4, respectively. The minimum growth rates ()5, 0.67 and )155) in both conditions indicated above were observed in 1994. The maximums for instantaneous growth rate (4.4% or 0.59%), growth rate per capita (0.23% or 0.03%) and annual population growth rates (85% or 11.41%) were observed in year 2009 and in year 1996 (Table 2). Both instantaneous growth rate and growth rate per capita were positively correlated (r = 0.958, P < 0.01), respectively (Fig. 1 and Table 1). The average growth rates and intrinsic rate of increases in relation to generation time were also compared both under ideal and random environments. The average growth rate (kr) and the intrinsic rate of increase (rr) were Table 1 Correlation of average total growth rates with annual, instantaneous and growth rate per capita Parameters Correlation values with average growth rates Change statistics Growth rates R R2 Adjusted R2 SE R2 F Sig. F Av. annual (random) Av. annual (ideal) Instantaneous Per capita 0.810 0.950 0.892 0.958 0.656 0.902 0.795 0.918 0.641 0.898 0.784 0.913 0.288 14.30 1.194 0.053 0.656 0.906 0.795 0.918 45.672 220.409 69.788 201.508 0.000 0.000 0.000 0.000  2011 Blackwell Publishing Ltd, Afr. J. Ecol., 49, 292–300 Population dynamics of Walia ibex 295 6 2 –2 n ea M 08 20 06 04 20 20 20 02 00 20 96 19 19 94 83 19 76 19 74 0 19 Growth rate values 4 Instantaneous growth rate growth rate per capita –4 –6 Census years Fig 1 Mean instantaneous and per capita growth rates of Capra walie at Simien Mountains National Park Table 2 Maximum, minimum and average growth rate values of Capra walie from 1969 to 2009 Values Years with Parameters measured Minimum Maximum Mean Minimum growth rate Maximum growth rate Instantaneous growth rate Growth rate per capita Annual population growth rate Intrinsic rate of increase (ideal) Growth rate (ideal) Intrinsic rate of increase (random) Growth rate (random) )5.0 ()0.67) )0.67()0.09) )155 ()20.8) )0.674 ()0.09) )155 ()20.8) )2.22 ()0.3) 0.00 (0) 4.4 (0.59) 0.23 (0.03) 85 (11.41) 0.243 (0.033) 85 (11.41) 0.86 (0.12) 2.36 (0.32) 2.6 (0.35) 0.03 (0.004) 19.5 (2.62) 0.04 (0.006) 18.5 (2.5) )0.184 ()0.025) 0.935 (0.13) 1994 1994 1994 1994 1994 1994 1994 2009 1996 2009 2009 2009 2009 2009 The numbers in parenthesis show percentile value. positively correlated both under ideal (r = 0.950, P < 0.01) and random environments (r = 0.810, P < 0.01). Estimates of growth rates under ideal and random environments revealed that the population grows by 18.4% or 2.5% under ideal environments with an intrinsic increase of 0.04 (0.006%) per year. However, under random environments, the population grows by 0.935% or 0.13% with an intrinsic rate of decrease )0.184 ()0.025%) per year (Fig. 2 and Table 2). Population size and structure estimates per home range The results of the population size the analyses per home range indicated that most of the population was inhabited in places where disturbances are less frequent like Cheneck and Sebat Minch. Dirni and Gich home ranges were inhabited relatively with more population than Muchilla  2011 Blackwell Publishing Ltd, Afr. J. Ecol., 49, 292–300 and Adarmaz. On the other hand, Buait ras and Sankaber habitats were inhabited by the lowest population sizes (Fig. 3). The mean ranks of the flock structure were 3.13, 3.88, 2.00 and 1.00 for males, females, juveniles and unidentified, respectively. The age distribution per sex and per home range was proportional to the population size in each habitat except that a few females were found in home ranges with frequent disturbances (Fig. 4). From all population, 23% of the population accounted for males older than 7 years and 2.3% for juveniles <2 years old. Discussion Gaillard et al. (2000) and Gordon et al. (2004) disclosed that long-term ecological studies of population dynamics in herbivores provide a detailed understanding of the effects 296 Kefyalew Alemayehu et al. Intrinsic rate of increase (rr) Average growth rates (ra) 2.0 1.0 06 08 20 04 20 00 02 20 20 96 19 20 94 19 19 83 76 19 74 19 69 72 19 19 64 0.0 19 Intrinsic rate of increase (rr) and average growth rate (ra) values 3.0 –1.0 –2.0 –3.0 Census years Population size value per year Fig 2 Mean of intrinsic rate of increase (rr) and average population growth rate (kr) of Capra walie population under random environments 250 2004 2007 200 2005 2008 2006 2009 150 100 50 0 Buait ras Sankaber Gich Cheneck Sebat Minich Dirni Muchila Adarmaz Home ranges Fig 3 Population size trends of Capra walie at each home range 450 Male Female Juveniles Unidentified Population size per sex 400 350 300 250 200 150 100 50 0 2004 2005 2006 2007 2008 2009 Census years Fig 4 Flock structure of Capra walie at Smien Mountains National Park  2011 Blackwell Publishing Ltd, Afr. J. Ecol., 49, 292–300 Population dynamics of Walia ibex of intrinsic and extrinsic factors for determining population size, growth and composition. It was also reported that the population growth rate is the central unifying concept of population dynamics (Sibly & Hone, 2002; Lewontin, 2003). Population growth rates can be accurately predicted from the fecundity and survival estimates. However, ecological and ⁄ or genetic factors were responsible for variation among populations in the fecundity and survival rates as well as to variation in the overall population growth rate (Reed, Nicholas & Stratton, 2007). The overall result of our study shown that the population growth rates of C. walie increased per year with great fluctuations. The population had negative growth rates (k < 1) in years 1976 and 1994 for both conditions. The main reasons for these negative growth rates were political instabilities of the years in the area, which then became proxy for habitat loss and fragmentation, livestock grazing, introduction of exotic species, agricultural expansion and overexploitation. It was also reported that habitat destruction and degradation, pollution, introduction of exotic species and over-exploitation were the causes for fluctuation of the growth rates (Frankham, 1994; Frankham, Ballou & Briscoe, 2004). Population pressure and competition for natural resources have been increased for several decades. These threatened both the livelihoods of local smallholders and the diverse fauna and flora of the SMNP (Grünenfelder, 2006). The overall fluctuations of the growth rates in particular and the fluctuation of the population dynamics of a species in general could also be caused by variation in the environment that causes the rates of birth and death in the population to vary from year to year (Giardina, Philippe & M¢ezard, 2002). It has been reported that the fragmentations of habitats have resulted in reduced, disparate populations that are prone to the effects of genetic bottlenecks resulting in a loss of genetic diversity (Mitrovski et al., 2007). Population fragmentation because of natural or human-induced activities is a widely recognized threat for endangered species in the wild (Frankham, Ballou & Broscoe, 2002). The negative effect of fragmentation is that each subpopulation will necessarily have a relatively low effective population size and therefore higher levels of inbreeding (Ferna¢ndez, Toro & Caballero, 2008). Inbreeding can potentially reduce population growth rates and increase extinction (Newman & Pilson, 1997). Recent study demonstrated that restored immigration rapidly reverses negative population growth rates of inbred populations (Hogg et al., 2006), because inbreeding  2011 Blackwell Publishing Ltd, Afr. J. Ecol., 49, 292–300 297 significantly reduces the growth and viability of juvenile and fitness related traits (Gallardo & Neira, 2005). The intrinsic rates of increases of C. walie under ideal conditions were positively correlated with the annual population growth rate but negative under random environments. This is because the maximum value of intrinsic rate of increase for a population is influenced by life history features, such as age at the beginning of reproduction, the number of young produced, and how well the young survive, all could be affected by environmental factors (Gaillard, Marco & Nigel, 1998). The negative intrinsic rate of increase can be attributed to the low variation in polymorphism at microsatellite loci that are usually highly variable in ungulates, suggesting a severe loss of genetic diversity in C. walie (Gebremedhin et al., 2009). This indicates that the genetic diversity of the species is decreasing and those with a higher intrinsic rate of increase will grow faster than one with a lower rate of increase (Gaillard, Marco & Nigel, 1998). Therefore, random environment with deterministic and stochastic factors affected negatively the growth rates of C. walie population. Our results also disclosed that C. walie populations are strongly age-structured with different age classes. Male C. walie older than 7 years tend to form larger groups and commonly seen in the borders of the park. However, females together with males aged between 2 and 7 years and with their kids inhabit in gorges and less disturbed habitats. It was also reported that females are more solitary than males outside of the breeding season. Instead, males form small groups with other males of similar age or size (Dunbar & Dunbar, 1981). Females form nursery groups during the birth season, rather than becoming solitary, as do many ungulates. This is owing to the risk of attack from large birds of prey (like eagles and vultures) (Dunbar, 1978).This pattern of association is reversed during the rut season, with females forming nursery groups and males isolating themselves from one another in competition (Dunbar, 1978). Age structures of the populations were characterized by a high proportion of old animals and exhibit more adult survival than juveniles’ exhibit. The average survivals of the juveniles (2.3%) were lower than the prime-aged males (2–7 years) (11.7%) of the total population. However, over 23% of the proportion accounts for males older than 7 years. This is because juvenile survivals and to a lesser extent fecundity, especially of young females, can vary considerably from year to year (Saether, 1997; Gaillard et al., 2000; Andrew et al., 2004). The high yearly 298 Kefyalew Alemayehu et al. variation in juvenile survival probably has multiple causes. Predation, low birth weight, early growth rates and late parturition (Singer et al., 1997) as well as genetic factors (Frankham, Ballou & Briscoe, 2004) have been reported to decrease juvenile survival in ungulates. Therefore, the population of C. walie exhibits the typical survival pattern of large vertebrates with a very high adult survival as in other ibex population reported in Gaillard et al. (2000). The survival of the juveniles (C. walie) was also affected by predators like leopards and vultures than the adults. It was also possible to see that the population size was concentrated in home ranges with low human and predator disturbances. From three districts found adjacent to the park, Debark district has five peasant associations residing inside the park and had more disturbances to the wildlife population in general and to C. walie in particular. On the other hand, Adiarkay and Janamora districts have one and zero peasant associations residing inside the park, respectively, and hence less disturbances as compared to Debark. In this population, although the trends of females and juveniles populations are increasing, there were variations in population size on year bases. The reasons for these variations were related to food resources, habitat quality, weather, diseases, interspecific competition, predation, human activities and population density account for the demographic variation observed among years within a population or among populations within a species (Gaillard, Marco & Nigel, 1998; Gebremedhin et al., 2009). Studies on other ungulates have disclosed that an interaction of year-to-year changes in weather for survival and reproduction may explain changes in population density in environments where large predators are very rare or absent (Saether, 1997; Post & Stenseth, 1999; Andrew et al., 2004). Therefore, age distribution and structure of wildlife affect the population dynamics of the species (Andrew et al., 2004) and hence C. walie. Conclusion Because of the effects of intrinsic and extrinsic factors, which determined the population size, growth and composition of species, the population dynamics of C. walie varied from year to year. Because of low the intrinsic rate of increase, the population tends to have low population growth rates per year. The low and declining intrinsic rate of increase implies that the genetic diversity of the species is decreasing, which will make the species unable to adapt the harsh climatic conditions and may lead to sudden extinction. The population had shown more adult survival than the prime-aged individuals had. The survival of the juveniles per home range was less than the adults’ survival. This was attributed to variations in food resources, climate variabilities, interspecific competition, predation and disturbances from human activities. Therefore, the population dynamics of C. walie was fluctuating because of fluctuations of the population growth rates and this intern affected by low intrinsic rate of increases. The overall effects became causes to variation in age and sex ratio, low effective population size, inbreeding and loss of genetic diversity. Habitat protection from human disturbances by stopping deforestation, agriculture, livestock grazing and translocation of some of the population to the adjacent home ranges will allow interbreeding among isolated population and increase genetic diversity of the species. 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