An ecological study of chimpanzees in a savanna woodland

From May, 1964, to September, 1965, the author made ecological and sociological studies of wild chimpanzees (Pan troglodytes) in Western Tanzania, East Africa. The vegetation of this area belongs to theBrachystegia andIsoberlinia savanna woodland. During the dry season, chimpanzees go out into the open forest and chiefly eat the hard seeds ofJulbernardia, Brachystegia, Isoberlinia, Pterocarpus, etc.The continuity of the group of chimpanzees is not stable but temporary, as has been reported byGoodall, etc. The author termed such a temporary group nomadic group. A big nomadic group, such as that consisting of 43 individuals at Filabanga, seems to be one unit of a chimpanzee's society.The nomadic range of the chimpanzees in the savanna woodland covers about 100 km² (201 km² in the Kasakati area). This is greater than that of the chimpanzees living in the forest, and such a large range has not been previously known among other non-human primates.This study was made possible by the Overseas Scientific Research Fund of the Ministry of Education.     

Tree growth in an African woodland savanna affected by disturbance

Questions: How does tree growth in a tropical woodland savanna vary as a function of size, and how is it affected by competition from neighbours, site attributes, and damage caused by disturbance? Location: western Zimbabwe. Methods: Trees of common species were tagged, mapped, and measured annually between 2001 and 2003 in a Kalahari sand woodland savanna. Diameter increments were analysed with mixed model regressions for the largest ramet in each genet. Stem diameter and damage, soil texture, and indices of competition at multiple spatial scales were used as covariates. Results: Stem diameter increased initially and then declined as a function of size in undamaged trees, which grew faster than damaged trees. Growth in damaged trees declined with size. No site differences were detected, and there was evidence for between‐tree competition on growth only in the fastest‐growing species, Brachystegia spiciformis. In several species the growth rate of the largest ramet increased as a function of the basal area of secondary ramets, contrary to expectations. For many species, the growth models showed poor explanatory power. Conclusions: Growth in Kalahari sand savanna trees varies as a function of size and changes in tree architecture caused by disturbance agents such as fire, frost, and elephant browsing. Disturbance may thus play an important role on vegetation dynamics through its effects on growth in the post‐disturbance phase. Growth is highly stochastic for some species in this system, and more deterministic in others. It is hypothesized that this dichotomy may be driven by differences in rooting depth among species.     

Sleeping site selection by savanna chimpanzees in Ugalla,Tanzania

We examined sleeping site selection by chimpanzees (Pan troglodytes) in the Ugalla savanna woodland area, western Tanzania, from 1994 to 2012. We established 488 km of line transects and recorded 379 chimpanzee beds within 30 m perpendicular to the transects. Comparisons between 60 × 60 m² quadrats containing new and recent beds and the remaining quadrats without beds along the transects indicated that evergreen forests accounted for disproportionately more area in quadrats with beds than in those without beds during both the dry and rainy seasons. In Ugalla, chimpanzees coexist with lions (Panthera leo) and leopards (Panthera pardus). They may sleep in forests to reduce predation risk by these carnivores, as trees are dense and the canopy is high and closed. The angle of slope was steeper in quadrats containing beds than in those without beds during the dry season, whereas the angle was less steep in quadrats with beds than in those without beds during the rainy season. Additionally, fewer beds were found further from forests. The distance between beds and forests during the dry season was shorter than that during the rainy season. Chimpanzees may sleep in or near forests and on slopes because of water pools in the valley forests along the slopes during the dry season. Quadrats with beds were at slightly higher altitude than those without beds during the rainy season; however, the difference was not significant during the dry season. The number of beds found in or close to feeding trees was not related to the fruiting period. Sleeping site selection by chimpanzees may be affected by predation pressure and water availability in the savanna woodland area.     

Abundance of trees and grasses in a woodland savanna in relation to environmental factors

The relationships of plant species associations and underlying environmental factors in a woodland savanna in South Africa were investigated. 40 plots were included with 25 tree and 17 grass species dominating the arboreal and ground cover. Correspondence Analysis described the relationships between soil moisture retention, soil nutrients and the abundance of trees and grasses. Dry matter indices represented the accumulated effects of rainfall, fire and grazing of the herbaceous layer. Variations in the abundance of plants corresponded to well-defined gradients of soil nutrients. The distribution of grass and tree species along the ordination axes indicated that soils with high water retention capacity and high nutrient contents provided a suitable substrate for many of the tree species sampled. However, grass species abundance was high in plots with porous soils and poor nutrient availability.     

Plant-food and tool transfer among savanna chimpanzees at Fongoli, Senegal

Transferring food is considered a defining characteristic of humans, as such behavior is relatively uncommon in other animal species save for kin-based transfer. Chimpanzees (Pan troglodytes) are one exception, as they commonly transfer meat among nonrelatives but rarely transfer other resources. New observations at Fongoli, Senegal, show habitual transfer of wild-plant foods and other non-meat resources among community members beyond transfers from mother to offspring. We explore various explanations for these behaviors with a focus on age- and sex-class patterns in transfer events. In a total of 27 of 41 cases, male chimpanzees at Fongoli transferred wild-plant foods or tools to females. Most other cases involved transfer among males or males taking food from females. In light of male–female transfer patterns at Fongoli, we examine four hypotheses that have been applied to food transfer in apes: (1) testing for male-coercive tendency (van Noordwijk and van Schaik, Behav Ecol Sociobiol 63:883–890, 2009), (2) costly signaling (Hockings et al. PLoS ONE 2:e886, 2007), (3) food-for-sex (Gomes and Boesch, PLoS ONE 4:5116, 2009), and (4) sharing-under-pressure (Gilby, Anim Behav 71:953–963, 2006). We also consider hypotheses posed to explain transfer among callitrichids, where such behavior is more common (Ruiz-Miranda et al. Am J Primatol 48:305–320, 1999). Finally, we examine variables such as patch and food size and food transport. We discuss our findings relative to general patterns of non-meat transfer in Pan and examine them in the context of chimpanzee sociality in particular. We then contrast chimpanzee species and subspecies in terms of non-meat food and tool transfer and address the possibility that a savanna environment contributes to the unusual pattern observed at Fongoli.     

High prevalence of simian immunodeficiency virus infection in a community of savanna chimpanzees

Simian immunodeficiency virus of chimpanzees (SIVcpz) has a significant negative impact on the health, reproduction, and life span of chimpanzees, yet the prevalence and distribution of this virus in wild-living populations are still only poorly understood. Here, we show that savanna chimpanzees, who live in ecologically marginal habitats at 10- to 50-fold lower population densities than forest chimpanzees, can be infected with SIVcpz at high prevalence rates. Fecal samples were collected from nonhabituated eastern chimpanzees (Pan troglodytes schweinfurthii) in the Issa Valley (n = 375) and Shangwa River (n = 6) areas of the Masito-Ugalla region in western Tanzania, genotyped to determine the number of sampled individuals, and tested for SIVcpz-specific antibodies and nucleic acids. None of 5 Shangwa River apes tested positive for SIVcpz; however, 21 of 67 Issa Valley chimpanzees were SIVcpz infected, indicating a prevalence rate of 31% (95% confidence interval, 21% to 44%). Two individuals became infected during the 14-month observation period, documenting continuing virus spread in this community. To characterize the newly identified SIVcpz strains, partial and full-length viral sequences were amplified from fecal RNA of 10 infected chimpanzees. Phylogenetic analyses showed that the Ugalla viruses formed a monophyletic lineage most closely related to viruses endemic in Gombe National Park, also located in Tanzania, indicating a connection between these now separated communities at some time in the past. These findings document that SIVcpz is more widespread in Tanzania than previously thought and that even very low-density chimpanzee populations can be infected with SIVcpz at high prevalence rates. Determining whether savanna chimpanzees, who face much more extreme environmental conditions than forest chimpanzees, are more susceptible to SIVcpz-associated morbidity and mortality will have important scientific and conservation implications.     

Topo-edaphic, floristic and physiognomic gradients of woody plants in a semi-arid African savanna woodland

The variation in topo-edaphic conditions, woodland composition and physiognomic structure of a semi-arid savanna woodland, namely the 59 400 ha Klaserie Nature Reserve, was studied with multivariate techniques. Spatial variation in the texture and chemistry of both the A-and B-horizons was substantial. One gradient of the A-horizon was of increasing clay, silt, organic matter, pH and conductivity, while a second gradient was of increasing rockiness, slope and gravel content, associated in part with upper landscape positions. Physiognomic structure of the woodland also displayed substantial spatial variation. Variation in tree density had the greatest effect on total canopy volume, and the density of coppice and dead individuals were closely correlated. Topo-edaphic variation, after the effect of vegetation composition had been accounted for, had a direct effect on woodland structure, as clay content of soils or rockiness influenced shrub density, and catenal position together with silt-or gravel-content of soils influenced coppice density. Ordination analyses identified that the included topo-edaphic variables accounted for a significant amount of floristic variation, but also showed that important environmental variables were omitted. Floristic variation of woody elements was of the nature of a large number of relatively equivalent, independent gradients rather than of a few simple primary gradients. Ten woodland types were identified by TWINSPAN which differed in their topo-edaphic and physiognomic character. Distinctive woodland assemblages were found on rocky outcrops or alluvial areas, on deep, sandy soils or on clay-or silt-rich soils. Colophospermum mopane formed the densest woodlands. Characteristics of the B-horizon were often dissimilar to those of the A-horizon, and seemed important for woodland composition.     

The effects of foraging ants on arboreal insect herbivores in an undisturbed woodland savanna

ABSTRACT.

• 1 A comparison was made of the insect fauna on paired Terminalia sericea, Burkea africana and Ochna pulchra trees; one tree in each pair was treated with Formex® to exclude ants from the canopy, and the other was designated the control.
• 2 Treatment with Formex banding to exclude ants did not influence plant phenology.
• 3 Pyrethrum knockdown samples from control trees had generally more insect individuals and insect species than samples from trees where ants were excluded.
• 4 Formex-treated trees had significantly less homopterous individuals and species than the control trees.
• 5 With the exception of ants and Homoptera, there was no difference in the insect guild composition and dominance ranking of various insect taxa, sampled by pyrethrum knockdown, between the control and Formex-treated trees.
• 6 T.sericea had significantly greater populations of both sessile and mobile Homoptera on the control trees than on the Formex-treated trees. A similar trend could be seen on B.africana. There were significantly more sessile homopterans on the control trees of O.pulchra than on the Formex-treated trees. Low numbers of mobile Homoptera were recorded on both control and Formex-treated O.pulchra trees, and numbers on control trees were fewer in comparison to numbers of mobile Homoptera on control T.sericea and B.africana trees.
• 7 It is concluded that the ants have similar effects on the insect communities of trees in a natural, undisturbed savanna as has been demonstrated on trees in agro-ecosystems, and on plants that are structurally adapted for mutualistic associations with ants.
• 8 Although slight, leaf damage by some leaf-feeding insects was greater on trees where ants had been excluded than on control trees that supported foraging ant populations.

     

An ecological study of small rodents in the woodland savanna of Liwonde National Park, Malawi

A community of small rodents was studied in the woodland savanna of Liwonde National Park, Malawi from September 1984 to June 1985. Seven species were recorded on two 11 ha grids, using a capture-mark-release technique. Three species ( Aelhomys chrysophilus, Acomys spinosissimus and Tatera leucogasler ) comprised 78% of all trapped individuals. Average population numbers fluctuated from 3 to 17 individuals/ha. The grid with the densest vegetation supported the greatest number of individuals. Highest population numbers occurred in the mid-dry season (when the grids appeared to act as refugia) and in the early wet season (due to recruitment of young animals). Areas which had been burned during the dry season did not support as many individuals as unburnt areas. Population survival rates were low, with only about 50% of individuals surviving to the following month. The number of individuals/ha in Liwonde NP was lower than in similar habitats in other parts of eastern Africa, probably because of the shorter rainfall season and the consequent strong seasonal fluctuations in food resources, reduced opportunity for reproduction, and overall low productivity of the ecosystem.     

The influence of cattle grazing on tree mortality after drought in savanna woodland in north Queensland

Abstract Live and dead trees were measured in macropod-grazed and cattle-grazed Eucalyptus woodland in north Queensland following a severe drought between 1992 and 1994. ANCOVA revealed no effect of grazing treatment on the proportion of drought death. Twenty-seven per cent of all tree species were killed by the drought and the value ranged from about 4% for Corymbia dallachiana (Benth.), K. D. Hlll & L. A. S. Johnson to 29% for the dominant species Eucalyptus xanthoclada Brooker and A.R.Bean, although differences were non-significant. There was also no significant difference in mortality between poles (< 10 cm d.b.h.) and trees (> 10 cm d.b.h.). The study highlights a natural (as in pre-European), catastrophic structural collapse of tropical eucalypt woodland. Presumably the dramatic declines in basal area as a result of drought are recovered during successive relatively wet years by thickening events, although clearly this severe drought and its after-effects warrant further study.     

Forest reserves and woodland savanna regeneration on the Sub-Saharan Massif of Jebel Marra,Democratic Republic of the Sudan

The effect of a forest reserve establishment on the natural forest ecosystem recovery and on the protection of valuable indigenous woody species in Jebel Marra, the Democratic Republic of the Sudan, is described. The following hypothesis is formulated: The vegetation of the southwestern slopes of Jebel Marra, when protected from periodic disturbance, may recover to almost fully regenerated hill woodland. Empirical stratified transect sampling methods were applied to both natural forest ecosystems within the reserve and the surrounding artificial systems. Frequencies, densities and diversities for all woody species were estimated by standard ecological indices. It was found that the establishment of the forest reserve has dramatically reshaped the distribution of woody species and a slow process of regeneration to Anogeissus hill woodland is taking place.     

Woody plant seed dispersal and gap formation in a North American subtropical savanna woodland: the role of domestic herbivores

The relationship between domestic cattle and vegetation change in a savanna woodland was evaluated with respect to dung deposition and the dispersal and establishment of mesquite (Prosopis glandulosa var. glandulosa, Mimosaceae), a cosmopolitan woody invader of grasslands in the southwestern USA. Dung deposited in autumn disintegrated rapidly, leaving patches of bare ground ranging from 50 to 900 cm². Herbaceous cover on gaps created by dung deposition recovered to levels comparable to neighboring vegetation by the end of the following growing season. Vegetation colonizing gaps consisted primarily of grasses not found in the surrounding vegetation. Dung deposition increased species diversity and spatial heterogeneity of the herbaceous vegetation and contributed to the development of a fine-grain mosaic of small patches of varying successional age-states.The role of cattle in facilitating the ingress and establishment of mesquite has broader implications with regard to the conversion of grasslands to woodlands. On the site with cattle, mesquite seedlings were found in 75% of dung pats surveyed in September (mean =4.2 seedlings per pat; maximum =50). Although seedling survival in dung (79%) was only 16% greater than that of mesquite emerging from seeds experimentally sown away from dung, no seedlings were found on areas without cattle. Mean (± SE) density of mesquite seedlings ranged from 12±2 to 15±2 m^-2 on the site with cattle. Seed densities away from parent plants averaged 10.7 m^-2 and 0.0 m^-2 on areas with and without cattle, respectively. Seed densities beneath adult plants were comparable between sites.The high density of seedlings on areas with cattle, in contrast to absence of seedlings on the area without cattle, suggests rates of invasion of grasslands by mesquite would have increased substantially in North America following the settlement and introduction of domestic ungulates. Prior to the introduction of livestock, poor seed dissemination and germination may have limited its Holocene spread.     

Artificial feeding of chimpanzees and baboons in their natural habitat

Chimpanzees in Gombe National Park, Tanzania have been given bananas since 1962. Attendance rates at the feeding area, aggregation sizes and the frequency of aggresson of chimpanzees and baboons were closely affected by the manner of feeding. Reduced access to food appeared most responsible for the increase in aggression. The advantages and disadvantages of artificial feeding are discussed.