Showing papers in "African Journal of Ecology in 1988"

Methods of estimating ungulate populations in tropical forests

Abstract: Summary Pellet group counts, drive counts and track counts were used to estimate population abundances of one small and four large species of duiker (Cephalophus sp.) in a moist evergreen forest in northeastern Zaire. Procedures to develop estimates based on line transect counts of pellet groups are described. The Fourier Series estimator proved to be useful for estimating densities of pellet groups. Comparisons were made between population abundance in heavily and lightly hunted areas, and between small and large species. The three census methods were consistent in showing no significant difference between animal abundance in the hunted populations or between abundances of the smaller species relative to the larger species. All methods showed potential as population indices for assessing trends of rare and elusive species in forest environments. Drive counts and pellet group counts may also be useful for estimating densities.

Seasonal migration by white‐eared kob in relation to resources

Abstract: Summary Previous studies suggest that ungulate migrations in savanna ecosystems follow seasonal changes in the distribution of food, water or both. These hypotheses were examined for a migratory population of over 800,000 white-eared kob in Boma National Park, S.E. Sudan. Movements into the dry season range in the northern part of the ecosystem were correlated with seasonally scarce supplies of both food and water. In the dry season range, kob concentrated at densities often exceeding 1000 km-2 in low-lying meadows adjacent to permanent water supplies that produced grass regrowth throughout the dry season, when other areas were unproductive. Grass growth during the dry season was dependent on residual soil moisture. Movements into the wet season range, however, were unrelated to the availability of either food or water. The low rainfall grasslands in the south may be preferred during the wet season because they are less prone to surface flooding than other areas, or because the short grasses in the south are more nutritious than the taller forms that predominate elsewhere. RESUMEE Des etudes anterieures suggerent que les migrations d'ongules dans les ecosystemes de savane suivent les changements saisonniers de la disponibilite en nourriture ou en eau ou les deux. Ces hypotheses ont ete examinees dans le cas d'une population migratrice de 800.000 cobes a oreilles blanches au P. N. Boma, au sud-est du Soudan. Les mouvements a l'interieur de l'habitat de saison seche dans la partie nord de l'ecosysteme ont ete mis en correlation avec le manque de disponibilites saisonnier de nourriture et d'eau. Dans l'habitat frequente en saison seche, les cobes etaient concentres a des densites depassant souvent 1000/km2, dans les prairies basses avoisinant un point d'eau permanent qui permettait que l'herbe repousse tout au long de la saison seche alors que les autres endroits restaient improductifs, la croissance de l'herbe durant la saison seche dependant de l'humidite residuelle dans le sol. Les mouvements a l'interieur de l'habitat de saison des pluies, d'autre part, ne sont pas relies a la disponibilite en nourriture ni en eau. Dans le sud, les prairies ou la pluviosite est faible peuvent ětre preferees durant la saison des pluies parce qu'elles risquent moins d'ětre inondees que les autres ou parce que les herbes courtes dans le sud sont plus nutritives que les especes plus hautes qui predominent ailleurs.

Wildebeest migration in the Kalahari

Abstract: Summary Between April 1981 and December 1984 aerial surveys were conducted in the northern Central Kalahari Game Reserve, the Lake Xau area and a larger area in southwestern Botswana. Range conditions were monitored in the northern Central Kalah, ri Game Reserve. The migration of wildebeest to surface water at Lake Xau was documented. Since the Kalahari wildebeest population has had severely restricted access to surface water for decades and this access is steadily diminishing, it is inferred that the existing population is smaller than it used to be and can be expected to decline further in the future.

Carbon isotopes as indicators of elephant diets and African environments

Abstract: Summary Stable carbon isotope ratios have been successfully used to assess modern animal diets and to reconstruct prehistoric diets of animals and humans (Vogel & van der Merwe, 1977; van der Merwe & Vogel, 1978; Burleigh & Brothwell, 1978; Vogel, 1978a; DeNiro & Epstein, 1978; Tieszen et al., 1979; Tieszen & Imbamba, 1980; Chisholm, Nelson & Schwarcz, 1982; Tauber, 1981). We have used 13C/12C ratio measurements of bone collagen to study the diets of African elephants in twelve wildlife refuges. These represent most of the habitats in which elephants live, including such diverse plant communities as primary rain forest, savanna woodland and desert. The δ13C values were found to have a simple linear relationship with tree density in most cases. When translated into relative amounts of dietary browse (C3 plants) and graze (C4 plants), the grass content is seen to be systematically under-represented, presumably due to inefficient metabolism. This does not affect the relationship between elephant diet and tree density, which has implications for the study of elephant-woodland interactions, and for reconstructions of past African environments.

Maximum rate of increase in the African Elephant

Abstract: Summary The theoretical maximum rate of increase for the African elephant is calculated at 7%. This figure agrees closely with the rate of increase observed at Addo Elephant Park, the highest rate of increase reported for elephants living under natural conditions. An elephant population increasing at the maximum rate soon reaches a stable age distribution in which 48% of the animals are older than 11 years of age, (the age of first reproduction) and 6.7% are calves (less than one year old). Several papers have reported frequencies of calves in natural populations of up to twice this percentage. Calculations are presented to show that such high calf frequencies are both theoretically impossible on a sustained basis, and internally inconsistent with the population data presented in these papers.

Small mammals of the Bale Mountains, Ethiopia

Abstract: Summary A sample of 535 small mammals, caught over a range of altitudes from 1500 to 4000 m in the Bale Mountains, on various expeditions from December 1971 to August 1986, enables the altitudinal zonation of the species to be delimited. The most abundant species, Lophuromys flavopunctatus, ranged from near the lower tree line at 1550 m, right up through the forested zones and onto the Afro-alpine moorland at 3900 m. The endemic Praomys albipes also ranged through the forest from 1550 to 3200 m, but was replaced in open habitats between 2400 and 3900 m by Stenocephalemys griseicauda and between 3000 and 4000 m by S. albocaudata, which was relatively more abundant than its congener at higher altitudes. Other moorland species, including Crocidura fumosa, Otomys typus, Lophuromys melanonyx and Arvicanthis blicki were also commonest at 3800–4000 m, but, like the Stenocephalemys spp., penetrated to lower altitudes in open habitats. Mus mahomet was confined to lower altitudes (1510–3000 m) and open habitats, apparently replaced by Mus triton, not previously recorded from Ethiopia, in forested habitats at middle altitudes (1950–2400 m).

Seasonal changes in the nutrient content of East African grassland vegetation

Abstract: Summary Significant seasonal changes in the concentrations of N, P, K, and Ca were observed in the herb layer vegetation at Nairobi National Park and Masai Mara Game Reserve in Kenya. These changes were related to the alternation of wet and dry seasons. Live forbs typically had the highest concentrations of all nutrients, especially N and Ca, at both locations. Standing dead and litter compartments showed less seasonal variation and had the lowest concentrations of all nutrients except Ca when compared with those of other compartments. Standing stocks of all nutrients were higher at Nairobi National Park than at Masai Mara due to larger litter and standing dead compartments resulting from lower grazing inten­ Sity and a lower frequency of fire. Most of the aboveground nutrients at Nairobi National Park appeared to be recycled through the decomposer pathway, while a large proportion of the standing stock at Masai Mara appeared to be recycled through the excreta of large mammalian herbivores and through fires. The crude protein content of the live grass compartment fell below maintenance levels required for ruminants (5% crude protein) during September 1980 and February 1981 at Nairobi National Park and during June and July 1980 at Masai Mara Game Reserve. Thus, herbivore populations in these preserves may be limited by shortages of nutritionally adequate food during dry seasons, as previously reported for other regions in East Africa. Resume Des variations saisonnieres significatives des concentrations en N, P, K et Ca ont ete observees dans Ia couche de vegetation au P.N. de Nairobi eta Ia reserve de chasse de Masa'i Mara, au Kenya. Ces variations ont ete mises en correlation avec l'alternance de saisons seches et saisons des pluies. Les herbes vivantes contenaient typiquement les plus hautes concentrations en chaque element, surtout N et Ca, aux deux endroits. Les herbes seches et Ia litiere montraient moins de variations saisonnieres et renfermaient les plus basses concentrations de chaque element sauf le Ca, comparees a celles des autres echantillons. La quantite totale d'elements nutritifs etait plus elevee au P.N. de Nairobi qu'a Masai Mara, due a unelitiereplus epaisse et a des herbes seches plus abondantes en raison d'une moins grande

Migration patterns of Thomson's gazelles and cheetahs on the Serengeti Plains

Abstract: Summary Monthly changes in abundance of Thomson's gazelles at 142 locations on the Serengeti Plains are presented over a 3½ year period. Numbers of gazelles on the eastern plains were strongly correlated with rainfall, whereas numbers in the central and western plains appeared to be related to other variables. Movements of female cheetahs and non-resident male cheetahs corresponded closely to the movements of Thomson's gazelles but those of resident male cheetahs remained relatively independent of the gazelle migration.

Biomass dynamics of grassland vegetation in Kenya

Abstract: Summary Seasonal changes in plant biomass in the herb layer were measured at Nairobi National Park and Masai Mara Game Reserve in Kenya from January 1980 to February 1981. Plant biomass fluctuated in response to seasonal rainfall, and live biomass was correlated with rainfall and soil moisture at both locations. Peak values for live biomass at Nairobi National Park occurred at the end of the long rains during the June 1980 sample and ranged from 138 to 197gm-2. Minimum values for live biomass at Nairobi occurred during a dry season in February 1981 and ranged from 8 to 39 g m-2. The standing dead and litter compartments were larger than the live compartment during every sample period at Nairobi National Park, and together often comprised more than 80% of the total above-ground biomass. Probably as a result of higher rainfall, peak values for live biomass at Masai Mara Game Reserve were higher than those at Nairobi. Again, peak biomass occurred during June following the long rains, and ranged from 218 to 294 gm-2. Minimum values for live biomass occurred during February 1981, and ranged from 10 to 48 g m-2. Standing dead and litter compartments were much smaller than at Nairobi National Park, reflecting more intense herbivore pressure and a greater frequency of fires at Masai Mara compared with that at Nairobi National Park.

Vital statistics of the baobab (Adansonia digitata)

Abstract: Summary Five populations of baobab trees in Zambia, Sudan, Mali, Kenya and Tanzania were measured to establish distribution of girth size classes. Absolute growth rates from rings or from empirical observations in each area were used to convert size into age classes. Baobab populations appear to be much younger than has generally been believed and only very few trees live to ages in excess of 400 years. Instantaneous mortality rates vary from 1 1 to 3–7% per year in the different areas. A lack of recruitment to the youngest age classes is caused by elephants in some areas but land-use changes due to increasing human populations and increased domestic animal numbers may also be responsible for low recruitment rates in other areas.

Fire behaviour and the invasion of Acacia sieberiana into savanna grassland openings

Abstract: Summary Following the recent decline in browsing and grazing pressures and changed fire regimes in Queen Elizabeth National Park, Uganda, Acacia thickets have encroached on grassland habitats important for grazing mammals. The objective of this research was to test experimentally the effects of fire behaviour, using simulated and natural fuel loading conditions, on A. sieberiana seedling and sapling regeneration. A high fire intensity (3200 kW m-1) in natural fuels stimulated high seedling emergence (172 seedlings m-2) compared to 6 seedlings m-2 without fire. Also a highly significant linear regression was established between percentage top-kill of seedlings and fire intensities. High fire intensities during late dry season fires were more effective in controlling sapling height growth than early dry season fires of low intensities. A conceptual diagram was developed to show the major factors and possible pathways leading to successful invasion by A. sieberiana into grassland openings of the savanna.

How much does a spotted hyaena eat? Perspective from the Namib Desert

Abstract: Summary The amount of food consumed by a clan of spotted hyaenas in the Namib desert was determined gravimetrically for 19 nights and the amount consumed by each individual was calculated according to its feeding time budget. At large, fleshy ungulate carcasses, each adult clan member ate about 8·7kg nightly, except for the bottom-ranking male, who obtained only half that amount per night. Skin and bone remains were consumed at a slower rate of Zkg/hyaena/night. Medium-sized ungulates were devoured rapidly so that each hyaena obtained more during such feeding nights than at large carcasses. Over a 29 day period, a hyaena clan con- sumed five cacasses at a rate of 4·0kg/hyaena/day, which compared well with previous estimates of average daily consumption in large social carnivores studied elsewhere. Annually, sixteen Namib hyaenas ate some 4·8% of the ungulate bio- mass, removing, in terms of numbers 14·3% of the gemsbok and 2·2% of the mountain zebra. This depletion did not appear to limit these populations.

Home range and movement of the common eland (Taurotragus oryx Pallas 1766) in Kenya

Abstract: Summary Data were collected in Kenya on the movements of individually recognizable wild eland over a 30-month period. Further information on movement was obtained from monthly ground counts of Nairobi National Park, and two aerial censuses of the Park and Athi Kapiti plains. Results indicated that adult male eland had restricted home ranges, but that females and juveniles carried out extensive seasonal movements between open grassland and bushed habitats. The numbers of eland in the Park were found to be related to rainfall over the previous two months in the areas outside the Park. It was concluded that females and juveniles were taking advantage of seasonal food abundance in open grassland areas, where the formation of large groups gives protection to small-sized juveniles.

Patterns of depletion in a black rhinoceros population in Luangwa Valley, Zambia

Abstract: Summary Black rhinos in Luangwa Valley, Zambia have been subjected to heavy illegal hunting since the late 1970s. A study population monitored by individual recognition decreased at an instantaneous rate of - 0.29 yr-1 between 1981 and 1985. Two-thirds of skulls found throughout Luangwa Valley between 1979 and 1985 were axed, indicating death from poaching. All age- and sex-classes of rhino were equally susceptible to being shot, presumably due to the high market-price of rhino horn.

Stratal distribution and resource partitioning of birds in the Knysna Forest, South Africa

Abstract: Summary Habitat subdivision and resource partitioning of the birds of the evergreen high forest of the southern Cape are investigated. Most species utilize a wide stratal range with insectivores predominating in the lower strata and mixed-feeders and frugivores in the upper strata. Members of the respective foraging guilds used a different stratum or were separated by differences in morphology or mass, suggesting different sized prey and limited competition.

Distribution of small rodents and shrews in a lowland rain forest zone of Nigeria, with observations on their reproductive biology

Abstract: Summary This paper describes the habitat preferences of small rodents and shrews from April 1984 to March 1985 in four types of vegetation in a lowland rain forest zone of Nigeria. The vegetation types were high forest, scrub, farmlands and teak plantations in Ogba Forest Reserve, Nigeria. A collection of 359 small mammals, consisting of six species of small rodents and four species of shrews, was made in the study area. The small rodents and their percentage composition were Mus musculoides (26.2%), Praomys tullbergi (16.2%), Mastomys natalensis (7.0%), Lophuromys sikapusi (4.5%), Lemniscomys striatus (2.5%), and Arvicanthis niloticus (1.1%). The shrews were Crocidura nigeriae (19.5%), C. crossei (12.3%), C.grandiceps (7.8%) and C. ftavescens manni (3.1%). The vegetational distribution of the small rodents and shrews is discussed. In the high forest, seven species of small mammals were caught; these were Crocidura nigeriae, C. crossei, C.grandiceps, C.flavescens manni, Mus musculoides, Praomys tullbergi and Lophuromys sikapusi. Mus musculoides, Crocidura nigeriae and Praomys tullbergi were more abundant in the high forest. All the species of small mammals recorded in the study area, except Arvicanthis niloticus, were found in the scrub. In the farmlands, all ten species of small mammals were trapped. Mus musculoides was the commonest species in the farmlands. Three species of shrews, Crocidura crossei, C. grandiceps and C.flavescens manni, and also two species of small rodents, Mus musculoides and Mastomys natalensis were caught in the teak plantation. The reproductive data for Mus musculoides, Crocidura nigeriae and Praomys tullbergi show that breeding in these species occurs throughout most months of the year. Fecundity appears to be maximal in the wet season in Mus musculoides and Crocidura nigeriae and in the dry season in the case of Praomys tullbergi.

Reproductive biology of the East African lungfish (Protopterus aethiopicus) in Mwanza Gulf, Lake Victoria

Abstract: Summary The population of lungfish (Protopterus aethiopicus (Heckel)) was sampled by bottom trawling for 12 months from June 1984 to May 1985. A total of 576 lungfish were investigated. The sex ratio in the population was 1 male : 1 -98 females. Average size at maturity was found to be 960cm total length (TL) but the smallest matured male measured 72-9 cm and the female 840 cm TL. It was not possible to establish spawning times and reproductive activity trends either from the variation in relative condition factor ‘kn’ or from gonadosomatic index (GSI). Whereas male lungfish seem to show no further increase in GSI after gonadal maturity stage III, females exhibit GSI values that vary directly with oocyte maturation and ovarian weights. Fat deposited along the gonads was found to be a better basis for assessing maturation and spawning in lungfish. The potential spawning period was found to be from September to May. Absence of lungfish with spent gonads over the 12-month period and the presence of different egg sizes in ovaries, suggest that the fish is a multiple spawner. Fecundity was found to range from 705 eggs (in 84-cm TL fish) to 14,922 eggs (in 130-cm TL Fish).

Territoriality of Guenther's dikdik in the Omo National Park, Ethiopia

Abstract: Summary Interrelationships between individuals and patterns of habitat use were studied in Guenther's dikdik, Rhyncotragus guentheri (Thomas), in the Omo National Park, Ethiopia, from November to December 1978, and from November 1981 to February 1982. Biotelemetrical studies were made of three dikdik in 1978 and of five in 1981/82. Direct observation of day and night behaviour was also carried out in 1981/82. Home-range size was estimated as 4–6 ha in 1978 and as 8-5-13-8 ha in 1981/82. This difference is attributed to the different climatic conditions between the years. Low precipitation in 1981/82 forced the dikdik to expand their range into an area rich in grassland. The identification of dung piles and antorbital scent marks was analysed in relation to the territorial boundaries. It is concluded that dung pile distribution is related to the territorial boundaries but that scent marks are of significance in orienting the animal within its territory. The significance of habitat types in the home-range area was estimated by superimposing convex polygons of 90% radio-fix points on the habitat map. It is concluded that the extensive Combretum-Sehima bush and patchily distributed Acalypha-Sanseviera thickets are the most important habitat types for dikdik. The former provides food and the latter shelter. Intraspecific variation of habitat preference from, open to closed is discussed in relation to yearly difference in population dispersion and individual differences during 1981/82. RESUMEE On a etudie les relations entre les individus et le type d'occupation du territoire chez le dik-dik de Guenther, Rhyncotrugus guentheri (Thomas) au P.N. Omo, en Ethiopie, en novembre et decembre 1978 et de novembre 1981 a fevrier 1982. Les etudes biotelemetriques ont ete faites sur 3 dik-dik en 1978 et sur 5 en 19Slj82. Le comportement a pu aussi ětre observe directement de nuit et de jour en 1981/82. On a estime le territoire a 4 6 ha en 1978 et a 8,5 a 13,8 ha en 1981/82. Ces differences ont ete attribuees aux conditions climatiques differentes entre ces annees. Les faibles precipitations de 1981/82 ont oblige les dik-dik aetendre leur territoire vers une region riche en herbages. L'occurrence d'excrements et les marquages par la glande antorbitale furent analyses, en relation avec les limites du territoire. On est arrivea la conclusion que les amas d'excrements sont lies aux limites territoriales mais que les marquages glandulaires ont pour fonction d'orienter l'animal a l'interieur du territoire. L'importance des types d'habitat pour le choix du territoire vital a eteetudiee en superposant des polygones convexes, avec 90% de points radio fixes, a la carte de l'habitat. On peut en conclure que la brousse extensive aCombretum-Sehima et les ilots parsemes de Acalyphu-Sanseviera representent les types d'habitat les plus importants pour ledik-dik, la premiere procurant la nourriture et les seconds, un abri. La variation intraspecifique de la preference d'un habitat plus ou moins ferme est mise en relation avec une difference annuelle de la dispersion de la population et des differences individuelles en 1981/82.

Age determination of the West African buffalo Syncerus caffer brachyceros and the constancy of tooth wear

Abstract: Summary Maxillae of 34 West African buffalo Syncerus caffer brachyceros were collected from three sites in Burkina Faso, West Africa, and age determined from tooth appearance and the enamel height of M1 according to the criteria of Grimsdell (1973) for Ugandan buffalo Syncerus caffer caffer. Good agreement between the two methods was found. Ground and decalcified sections were prepared from M1 and the interradicular cementum lines counted. Although this gave inconsistent results in terms of assumed age compared with the other two methods, it is concluded that agreement was sufficiently close to suggest that the rate of attrition with age was similar in both populations.

The feeding ecology of the African lily trotter Actophilornis africanus (Gmelin) at Lake Naivasha, Kenya

Abstract: Summary The only feeding habitats available to African lily trotters, Actophilornis africanus (Gmelin), at Lake Naivasha are mats of the alien water fern, Salvinia molesta Mitch. This has replaced the native floating leaved water lily beds. Lily trotters were able to use these mats, taking invertebrate food items from the surface or turning plants over and pecking at the rootlets. Pecking rates and turning rates responded to the nature of the available food, with pecking rates high and turning rates low when terrestrial arthropods were found on the mat surface. Both pecking rates and turning rates were low when large aquatic food items, such as the swamp worm (Alma emeni Michaelsen), were available. Pecking rates and turning rates were both high when the predominant food items were aquatic insect larvae. The largest of these (hydrophilid larvae) were taken in preference to the smaller but commoner chironomid larvae. Colonization of the mats of S. molesta by invertebrates was low if the mats were affected by wind action but higher if they were constrained by enclosure or stranding; mats with higher invertebrate densities supported more feeding lily trotters.

Age determination of the African buffalo, Syncerus coffer (Sparrman) in Zimbabwe

Abstract: Summary Age determination methods using teeth are described for African buffalo in Matusadona National Park, Kariba, Zimbabwe. Tooth eruption stages and age classes for sub-adult animals were established by reference to a seasonal breeding peak and known dates of death. Teeth in adult animals were allocated age classes based on wear using measurements of crown height and by reference to previously published material. Layering in the dental cement indicated the deposition of one cementum line per annum and line counts were used to assign chronological ages to individual animals. Regressions of wear on age were confirmed by independent counts of cementum lines using a predictive wear model.

Successional patterns of aquatic macrophytes in Jebba Lake, Nigeria

Abstract: Summary Macrophyte succession in Jebba Lake, Nigeria, was observed through the first four years after impoundment. Two distinct serai phases, a floating fern phase and a draw-down flora phase could be recognized. The floristic composition of the macrophyte vegetation was also investigated to check earlier predictions (Obot & Mbagwu, 1986) on the probable structure of the macrophyte flora. The failure of obligate floating macrophytes such as Pistia, Azolla and Salvinia to establish in the lake as predicted is discussed. However, rooted emergent macrophytes were observed to be more successful than would be expected from the predictions.

First steps in the ecology of the Bamingui‐Bangoran National Park, Central African Republic

Abstract: Summary A description is given of the 11,560 km2 Bamingui-Bangoran National Park situated in the mid-Sudanian phytogeographic domain of the Central African Republic. Attention is drawn to the interest of the ecology of this little-known zone, which lies between north-south and east-west ecotones, of the sahel-tropical forest and oriental region west Africa, respectively. Preliminary collections of plants and small mammals were made. An analysis of the flora and the large mammals observed suggests a predominantly West African affinity. The sub-specific endemism shown by the large mammals appears more probably linked to Pleistocene isolation by the Chari-Logone river system, than to a mega Lake Chad as has been postulated elsewhere.

Mima mounds in Kenya–a case of mistaken identity

Abstract: Summary Earth mounds at seven sites in upland areas of Kenya were examined. Termite activity was recorded from 91% of mounds and the major termite genus present was Odontotermes. Generally, signs of the mole rat, Tachyoryctes splendens were few and were present on only 18% mounds. All termite activity was mound-centred but only at Kiserian were mounds obvious centres for mole rat activity. At Molo, where Tachyoryctes were abundant, neither mounds nor much sign of termite activity were observed. The data are discussed in relation to the work of Cox and Gakahu. No convincing evidence was found to support the conclusion made by these workers for a mole rat origin of large earth mounds. The weight of the data suggests that a termite origin for these mounds is more likely.