NRU :: Browsing by Author "Lwanga, Jeremiah S."

Browsing by Author "Lwanga, Jeremiah S."

Now showing 1 - 15 of 15

Assessing Fern Diversity: relative species richness and its environmental correlates in Uganda
(Biodiversity & Conservation, 1998) Lwanga, Jeremiah S.; Balmford, Andrew; Badaza, Rose
Techniques for the rapid quantification of tropical biodiversity are of critical importance in deciding where to invest scarce conservation resources. Here we describe a simple survey method for assessing species-level richness of a poorly known plant group, the pteridophytes. We then illustrate the use of a powerful, rarefaction- based technique of controlling for inevitable differences in sampling effort to calculate the relative species richness of our study sites. Lastly, we explore how closely observed patterns of relative species richness of Ugandan forests are correlated with a suite of simple environmental variables. We find that fully 75% of the variance in our estimate of fern diversity can be predicted from just two measures: soil fertility (scored as C/N ratio, itself related to rainfall); and distance from the nearest putative Pleistocene refugium.
Changes in Elephant Abundance Affect Forest Composition or Regeneration?
(Biotropica, 2014) Omeja, Patrick A.; Jacob, Aerin L.; Lwanga, Jeremiah S.; Tumwesigye, Charles; Chapman, Colin A.
While overall numbers of African elephant have declined dramatically in recent times, some populations are now confined to protected areas and are locally overabundant—an undesirable situation for both biodiversity conservation and elephants. In forested protected areas, options to manage elephants are limited because it is difficult to safely approach animals, yet it is vital that these populations are managed because browsing by elephants can dramatically alter forest ecosystems. Using data collected over 50 yr in Kibale National Park, Uganda, we examine the prediction that increasing elephant numbers and associated changes in their foraging behavior have caused a shift in tree community composition. Although the relative abundance of elephants increased significantly between 1996 and 2010, the population structure of their preferred tree food species did not change, nor did tree community composition change in favor of species able to re-sprout after elephant damage. Furthermore, over the last 50 yr Kibale elephants have not become more selective foragers, as would be expected if more nutritious tree species were declining. However, elephants are more abundant in disturbed areas dominated by shrubs and grasses and appear to have arrested forest succession in these areas. At their current abundance, elephants have not selectively altered the composition of intact old growth forest, but they do inhibit the regeneration of disturbed areas.
Complementarity and the Use of Indicator Groups for Reserve Selection in Uganda
(Nature, 1998) Howard, Peter C.; Kigenyi, Fred W.; Baltzer, Michael; Lwanga, Jeremiah S.; Matthews, Roger A.; Balmford, Andrew
A major obstacle to conserving tropical biodiversity is the lack of information as to where efforts should be concentrated. One potential solution is to focus on readily assessed indicator groups, whose distribution predicts the overall importance of the biodiversity of candidate areas. Here we test this idea, using the most extensive data set on patterns of diversity assembled so far for any part of the tropics. As in studies of temperate regions we found little spatial congruence in the species richness of woody plants, large moths, butterflies, birds and small mammals across 50 Ugandan forests. Despite this lack of congruence, sets of priority forests selected using data on single taxa only often captured species richness in other groups with the same efficiency as using information on all taxa at once. This is because efficient conservation networks incorporate not only species-rich sites, but also those whose biotas best complement those of other areas. In Uganda, different taxa exhibit similar biogeography, so priority forests for one taxon collectively represent the important forest types for other taxa as well. Our results highlight the need, when evaluating potential indicators for reserve selection, to consider cross-taxon congruence in complementarity as well as species richness.
Elephants, Selective Logging and Forest Regeneration in the Kibale Forest, Uganda
(Journal of Tropical Ecology, 1996) Struhsaker, Thomas T.; Lwanga, Jeremiah S.; Kasenene, John M.
The Kibale Forest, western Uganda, is the only site where studies have compared the impact of elephants on rainforest regeneration in logged and unlogged control areas. Elephants used heavily logged areas more than lightly logged and unlogged areas. Forest gaps were used more by elephants than closed-canopy areas and large gaps more than small ones. Gaps were larger in logged than unlogged forest. There were lower densities of young trees (saplings and poles) and a higher incidence of elephant damage to them in heavily logged forest than in lightly logged and unlogged sites. Elephant use of an area and damage to young trees was inversely or unrelated to the density of young trees and directly related to the density of herbaceous tangle. Heavy logging resulted in large areas of herbaceous tangle, which attracted elephants who suppressed forest regeneration by damaging young trees and perpetuating the herbaceous tangle. The tangle directly competed with regeneration of young trees while also attracting elephants and rodents (seed and seedling predators) and facilitating increased windthrow of trees. Selective browsing of young trees by elephants affected rates of regeneration, growth form and species composition. Rather than remove elephants, a more effective and humane approach to long-term management of logging is to reduce logging offtake and incidental damage caused by timber extraction.
Floristic heterogeneity between forested sites in Kibale National Park, Uganda: insights into the fine-scale determinants of density in a large-bodied frugivorous primate
(Journal of animal ecology, 2009) Potts, Kevin B.; Chapman, Colin A.; Lwanga, Jeremiah S.
Factors regulating the density of consumer populations include both top-down (predation effects and disease) and bottom-up (resource availability and quality) components. Although the relative influence of each component is widely debated (e.g. Polis & Strong 1996; Schmitz, Hambäck & Beckerman 2000; Terborgh et al. 2001), it is likely that top-down and bottom-up processes play synergistic roles in limiting consumers (Krebs et al. 1995). Disentangling the relative effects of predators vs. resources ultimately requires either eliminating or controlling for one of these variables, thereby assessing the impact of the other (Moen & Oksanen 1998). Similarly, bottom-up and top-down regulatory factors may exert both spatial and temporal influences on consumers, and a complete understanding of how the environment limits populations requires examination of both factors. For example, Brown, Mehlman & Stevens (1995) found that the spatial distribution of abundance within North American bird species was well explained by concomitant spatial environmental variability that was relatively fixed over time. However, Ives & Klopfer (1997), building on Brown et al.’s (1995) work, suggested that similar spatial patterning could be created from temporal environmental variation without a fixed spatial component. Tropical forests are ideal sites in which to simultaneously incorporate both spatial and temporal components in understanding the determinants of density in vertebrates, particularly frugivorous species, as such ecosystems generally exhibit considerable spatiotemporal variability in fruiting phenology (van Schaik, Terborgh & Wright 1993; Condit et al. 2002; Cannon et al. 2007). Furthermore, the great apes (family Hominidae), the vast majority of which inhabit tropical forests (Campbell et al. 2007), represent a model taxon in which to address the role of bottom-up processes in regulating vertebrate frugivores. With some exceptions, most great apes are not subject to notable mortality risk from natural predators (Miller & Treves 2007), thus removing (or at least diminishing) the effect of top-down processes. We assessed which fine-scale ecological characteristics are potentially limiting the density of chimpanzees (Pan troglodytes Blumenbach, 1799) by comparing the spatiotemporal availability of resources between the home ranges of two communities of known size inhabiting Kibale National Park (KNP), Uganda. Chimpanzees are large-bodied, wide-ranging frugivorous apes with home ranges of c. 8–40 km2. The two communities included in this study are separated by only 12 km (or approximately one to three home ranges), and that at Ngogo (hereafter referred to as the ‘high-chimpanzee-density’ site) is the largest and most densely populated chimpanzee community currently known, with over 155 members (5·1 individuals km−2; Mitani & Watts 2005; Potts 2008), compared to c. 50 chimpanzees (1·5 individuals km−2) at Kanyawara (hereafter referred to as the ‘low-chimpanzee-density’ site; Muller & Wrangham 2004). Detailed long-term observations from this population suggest that other extrinsic variables (both top-down and bottom-up factors) not explicitly dealt with here, including disease, inter-specific niche overlap, predation, and/or non-fruit resource availability have played relatively limited roles in influencing spatial variations in chimpanzee density in KNP (Potts 2008). This population therefore presents an ideal model for isolating the effects of fruit resource availability in both space and time on the population ecology of large-bodied tropical frugivores.
Foci of Endemic Simian Immunodeficiency Virus Infection in Wild-Living Eastern Chimpanzees (Pan troglodytes schweinfurthii)
(Journal of virology, 2003) Santiago, Mario L.; Lukasik, Magdalena; Kamenya, Shadrack; Lwanga, Jeremiah S.; Hahn, Beatrice H.
Simian immunodeficiency virus of chimpanzees (SIVcpz) is the immediate precursor to human immunodeficiency virus type 1 (HIV-1), yet remarkably, the distribution and prevalence of SIVcpz in wild ape populations are unknown. Studies of SIVcpz infection rates in wild chimpanzees are complicated by the species' endangered status and by its geographic location in remote areas of sub-Saharan Africa. We have developed sensitive and specific urine and fecal tests for SIVcpz antibody and virion RNA (vRNA) detection and describe herein the first comprehensive prevalence study of SIVcpz infection in five wild Pan troglodytes schweinfurthii communities in east Africa. In Kibale National Park in Uganda, 31 (of 52) members of the Kanyawara community and 39 (of ∼145) members of the Ngogo community were studied; none were found to be positive for SIVcpz infection. In Gombe National Park in Tanzania, 15 (of 20) members of the Mitumba community, 51 (of 55) members of the Kasekela community, and at least 10 (of ∼20) members of the Kalande community were studied. Seven individuals were SIVcpz antibody and/or vRNA positive, and two others had indeterminate antibody results. Based on assay sensitivities and the numbers and types of specimens analyzed, we estimated the prevalence of SIVcpz infection to be 17% in Mitumba (95% confidence interval, 10 to 40%), 5% in Kasekela (95% confidence interval, 4 to 7%), and 30% in Kalande (95% confidence interval, 15 to 60%). For Gombe as a whole, the SIVcpz prevalence was estimated to be 13% (95% confidence interval, 7 to 25%). SIVcpz infection was confirmed in five chimpanzees by PCR amplification of partial pol and gp41/nef sequences which revealed a diverse group of viruses that formed a monophyletic lineage within the SIVcpzPts radiation. Although none of the 70 Kibale chimpanzees tested SIVcpz positive, we estimated the likelihood that a 10% or higher prevalence existed but went undetected because of sampling and assay limitations; this possibility was ruled out with 95% certainty. These results indicate that SIVcpz is unevenly distributed among P. t. schweinfurthii in east Africa, with foci or “hot spots” of SIVcpz endemicity in some communities and rare or absent infection in others. This situation contrasts with that for smaller monkey species, in which infection rates by related SIVs are generally much higher and more uniform among different groups and populations. The basis for the wide variability in SIVcpz infection rates in east African apes and the important question of SIVcpz prevalence in west central African chimpanzees (Pan troglodytes troglodytes) remain to be elucidated.
Forest succession in Kibale National Park, Uganda: implications for forest restoration and management
(African Journal of Ecology, 2003) Lwanga, Jeremiah S.
Forest succession was studied in four plots in former grasslands at the Ngogo study area in Kibale National Park, Uganda. The plots were located in areas that had been protected from fire for 0.58, 25, 9 and ≈30 years for plots 1, 2, 3 and 4, respectively. Species richness reflected the length of time that the plot had been protected from fire; it was highest in plot 4 and lowest in plot 1. Species density, stem density and basal area were all highest in plot 4 and lowest in plot 1. The species densities of plots 2 and 3 were not different. Similarly, plots 2 and 4 did not differ with regard to stem density or basal area. Animal seed dispersers played a vital role in the colonization of grasslands by forest tree species.
The influence of forest variation and possible effects of poaching on duiker abundance at Ngogo, Kibale National Park, Uganda
(African Journal of Ecology, 2006) Lwanga, Jeremiah S.
Duikers were censused at the Ngogo study area, Kibale National Park, Uganda, between July 2002 and August 2004. Censuses were conducted along three transects, of which, two (colonizing forests 1 and 2) were located in colonizing forests naturally replacing anthropogenic grasslands and one in old growth forest. Colonizing forest 1 was more prone to poaching than both colonizing forest 2 and the old growth forest that were closest to the research camp. Duikers that were actually sighted were identified to species, red or blue. However, on some occasions, duikers were detected by alarm calls and/or movements as they fled; these were simply recorded as duikers. Duiker abundance, regardless of species or mode of detection, was higher in colonizing forest 2 than colonizing forest 1 and the old growth forest. However, when the analysis was restricted only to duikers that were sighted, and hence identified to species, red duiker abundance was highest in colonizing forest 2 followed by the old growth forest and was lowest in colonizing forest 1; all these differences were significant. Blue duiker abundance was lowest in the old growth forest despite its proximity to the research camp; however, this was only significantly lower than in colonizing forest 2. Apart from colonizing forest 1, red duikers were significantly more abundant than blue duikers in the other two forest sections. This study suggests that forests colonizing anthropogenic grasslands may support more duikers than old growth forests; poaching in colonizing forest 1 has a severe impact on the duiker population and, red duikers are affected more severely by poaching than blue duikers.
Intensive Tree Planting Facilitates Tropical Forest Biodiversity and Biomass accumulation in Kibale National Park, Uganda
(Forest Ecology and Management, 2011) Omeja, Patrick A.; Chapman, Colin A.; Obua, Joseph; Lwanga, Jeremiah S.; Jacob, Aerin L.; Wanyama, Frederick; Mugenyi, Richard
The extensive area of degraded tropical land and the calls to conserve forest biodiversity and sequester carbon to offset climate change demonstrate the need to restore forest in the tropics. Deforested land is sometimes replanted with fast-growing trees; however, the consequences of intensive replanting on biomass accumulation or plant and animal diversity are poorly understood. The purpose of this study was to determine how intensive replanting affected tropical forest regeneration and biomass accumulation over ten years. We studied reforested sites in Kibale National Park, Uganda, that were degraded in the 1970s and replanted with five native tree species in 1995. We identified and measured the size of planted versus naturally regenerating trees, and felled and weighed matched trees outside the park to calculate region-specific allometric equations for above-ground tree biomass. The role of shrubs and grasses in facilitating or hindering the establishment of trees was evaluated by correlating observed estimates of percent cover to tree biomass. We found 39 tree species naturally regenerating in the restored area in addition to the five originally planted species. Biomass was much higher for planted (15,675kg/ha) than naturally regenerated trees (4560kg/ha), but naturally regenerating tree regrowth was an important element of the landscape. The establishment of tree seedlings initially appeared to be facilitated by shrubs, primarily Acanthus pubescens and the invasive Lantana camara; however, both are expected to hinder tree recruitment in the long-term. Large and small-seeded tree species were found in the replanted area, indicating that bird and mammal dispersers contributed to natural forest restoration. These results demonstrate that intensive replanting can accelerate the natural accumulation of biomass and biodiversity and facilitate the restoration of tropical forest communities. However, the long-term financial costs and ecological benefits of planting and maintaining reforested areas need to be weighed against other potential restoration strategies.
Localized tree mortality following the drought of 1999 at Ngogo, Kibale National Park, Uganda
(African Journal of Ecology, 2003) Lwanga, Jeremiah S.
The first half of 1999 was unusually dry at Ngogo, and caused leaves to dry on most trees throughout the study area. With the return of the rains in the second half of the year, trees on deeper soils recovered. In the year following the drought, massive tree mortality occurred along ridges and on hill-tops that happened to have shallow soils. This study investigated which species were susceptible to the drought in a locality with shallow soils.
Primate Community Dynamics in Old Growth Forest over 23.5 Years at Ngogo, Kibale National Park, Uganda: Implications for Conservation and Census Methods
(International Journal of Primatology, 2000) Mitani, John C.; Struhsaker, Thomas T.; Lwanga, Jeremiah S.
Few data exist regarding long-term changes in primate populations in old-growth, tropical forests. In the absence of this information, it is unclear how to assess population trends efficiently and economically. We addressed these problems by conducting line-transect censuses 23.5 years apart at the Ngogo study area in Kibale National Park, Uganda. We conducted additional censuses over short time intervals to determine the degree to which the temporal distribution of censuses affected estimates of primate numbers. Results indicate that two species, blue monkeys and red colobus, may have experienced significant reductions over the past 23.5 years at Ngogo. In contrast, five other species, baboons, black-and-white colobus, chimpanzees, mangabeys, and red-tailed guenons, have not changed in relative abundance. Additional findings indicate that different observers may vary significantly in their estimates of sighting distances of animals during censuses, thus rendering the use of measures of absolute densities problematic. Moreover, censuses conducted over short periods produce biased estimates of primate numbers. These results provide guidelines for the use of line-transect censuses and underscore the importance of protecting large blocks of forests for primate conservation.
Primate Populations and Their Interactions with Changing Habitats
(International Journal of Primatology, 2008) Isabirye-Basuta, Gilbert M.; Lwanga, Jeremiah S.
Given that 90% of nonhuman primates depend on tropical forests, the most effective way to conserve them must emphasize the conservation of tropical forest habitats. To achieve this effectively, we need to address root causes of forest disturbance in developing nations: poverty, high population growth rates, crippling foreign debts, and the overdependence on tree and land resources. Moreover, it is now generally accepted that most primate populations will in future live in modified forest habitats. Studies of how primate populations respond to forest habitat modifications are therefore critical to future primate conservation. Currently most studies of primate responses to forest habitat alterations are difficult to interpret owing to differences in research methods and lack of information on the past histories of the modified forests. We review potential factors that may have to be considered while evaluating primate responses to forest habitat changes such as degradation and fragmentation.
Spatial distribution of primates in a mosaic of colonizing and old growth forest at Ngogo, Kibale National Park, Uganda
(Primates, 2006) Lwanga, Jeremiah S.
Primate censuses were conducted in a mosaic of colonizing (two locations) and old-growth forests using line transect methods at the Ngogo study site, Kibale National Park, Uganda. Black and white colobus monkeys (Colobus guereza) were encountered more frequently in the colonizing forests than in the old growth forest, while chimpanzees (Pan troglodytes) were encountered more frequently in the old growth forest than in colonizing forests. Although not significant, results suggest that blue monkeys (Cercopithecus mitis) frequented colonizing forests more often than old growth forest. The encounter rates of mangabey (Lophocebus albigena), and redtail (Cercopithecus ascanius) groups were ambiguous with their density being higher in some colonizing forests but not others as compared to old-growth forest. No significant differences were detected for baboons (Papio anubis), L’hoest’s (Cercopithecus lhoesti), and red colobus monkeys (Piliocolobus tephroscales). The conversion of forests to farmland is one of the major problems encountered in primate conservation. This study shows that secondary forests replacing anthropogenic grasslands have the potential of supporting some primate species such as black and white colobus, redtail monkeys, and possibly blue monkeys. Therefore, such areas should not be given up but should be conserved for the benefit of primates that can survive in secondary forests; as the forests mature further, primate species that are adapted to old growth forest will colonize the area provided there is a nearby source.
Urinary C-peptide Tracks Seasonal and Individual Variation in Energy Balance in Wild Chimpanzees
(Hormones and Behavior, 2009) Thompson, Melissa Emery; Muller, Martin N.; Lwanga, Jeremiah S.; Potts, Kevin B.
C-peptide of insulin presents a promising new tool for behavioral ecologists that allows for regular, non-invasive assessment of energetic condition in wild animals. C-peptide is produced on an equimolar basis with insulin, thus is indicative of the body's response to available glucose and, with repeated measurement, provides a biomarker of energy balance. As yet, few studies have validated the efficacy of C-peptide for monitoring energy balance in wild animals. Here, we assess seasonal and interindividual variation in urinary C-peptide concentrations of East African chimpanzees (Pan troglodytes schweinfurthii). We assayed 519 urine samples from 13 adult male chimpanzees in the Kanyawara community of Kibale National Park, Uganda. C-peptide levels were significantly predicted by the total amount of fruit and the amount of preferred fruit in the diet. However, chimpanzees had very low C-peptide titers during an epidemic of severe respiratory illness, despite highly favorable feeding conditions. Kanyawara males had significantly lower C-peptide levels than males at Ngogo, a nearby chimpanzee community occupying a more productive habitat. Among Kanyawara males, low-ranking males had consistently higher C-peptide levels than dominant males. While counterintuitive, this result supports previous findings of costs associated with dominance in male chimpanzees. Our preliminary investigations demonstrate that C-peptide has wide applications in field research, providing an accessible tool for evaluating seasonal and individual variation in energetic condition, as well as the costs of processes such as immune function and reproduction.
Variation in Woody Species Abundance and Distribution in and around Kibale National Park, Uganda
(International Scholarly Research Notices, 2012) Okiror, Paul; Chono, Jane; Nyamukuru, Antonia; Lwanga, Jeremiah S.; Sasira, Phionah; Diogo, Paul
Several protected areas in Uganda are increasingly facing encroachment making farmlands indispensable hubs for biodiversity conservation. A comparative study was conducted comprising a protected area in Kibale National Park and surrounding farmlands to establish how farmlands mimic the forest floristic structure. Study results show very low similarity between the forest and farmland ecosystems (CCj = 0.11). A total of 50 and 29 species were identified in the forest and, farmland, respectively; 8 were shared. Importance value indices of woody species in the forest ranged from 0.3 to 29.9 with Celtis durandii being the most important while those in the farmland were 1.9–79.2, Eucalyptus grandis, having the highest index. Woody species diversity and evenness were higher in the forest ecosystem (H = 3.46, J = 0.85) compared to the farmland (H = 2.72, J = 0.79). The 10– <20 cm diameter class was the lowest in both ecosystems. Communities adjacent to the park should be educated about the value of the park and conservation in general. Since adjacent farmlands provide important ecotones to the park, on-farm indigenous tree retention and planting are required. Further research on threatened species is needed to enhance conservation in and around KNP.

Browsing by Author "Lwanga, Jeremiah S."

Results Per Page

Sort Options