Okavango Delta Region Research Articles

Environmental drivers behind the exceptional increase in cyanobacterial blooms in Okavango Delta, Botswana

The Okavango Delta region in Botswana experienced exceptionally intense landscape-wide cyanobacterial harmful algal blooms (CyanoHABs) in 2020. In this study, the drivers behind CyanoHABs were determined from thirteen independent environmental variables, including vegetation indices, climate and meteorological parameters, and landscape variables. Annual Land Use Land Cover (LULC) maps were created from 2017 to 2020, with ∼89% accuracy to compute landscape variables such as LULC change. Generalized Additive Models (GAM) and Structural Equation Models (SEM) were used to determine the most important drivers behind the CyanoHABs. Normalized Difference Chlorophyll Index (NDCI) and Green Line Height (GLH) algorithms served as proxies for chlorophyll-a (green algae) and phycocyanin (cyanobacteria) concentrations. GAM models showed that seven out of the thirteen variables explained 89.9% of the variance for GLH. The models showcased that climate variables, including monthly precipitation (8.8%) and Palmer Severity Drought Index- PDSI (3.2%), along with landscape variables such as changes in Wetlands area (7.5%), and Normalized Difference Vegetation Index (NDVI) (5.4%) were the determining drivers behind the increased cyanobacterial activity within the Delta. Both PDSI and NDVI showed negative correlations with GLH, indicating that increased drought conditions could have led to large increases in toxic CyanoHAB activity within the region. This study provides new information about environmental drivers which can help monitor and predict regions at risk of future severe CyanoHABs outbreaks in the Okavango Delta, Botswana, and other similar data-scarce and ecologically sensitive areas in Africa.Plain Language Summary: The waters of the Okavango Delta in Northern Botswana experienced an exceptional increase in toxic cyanobacterial activity in recent years. Cyanobacterial blooms have been shown to affect local communities and wildlife in the past. To determine the drivers behind this increased bloom activity, we analyzed the effects of thirteen independent environmental variables using two different statistical models. Within this research, we focused on vegetation indices, meteorological, and landscape variables, as previous studies have shown their effect on cyanobacterial activity in other parts of the world. While driver determination for cyanobacteria has been done before, the environmental conditions most important for cyanobacterial growth can be specific to the geographic setting of a study site. The statistical analysis indicated that the increases in cyanobacterial bloom activity within the region were mainly driven by persistent drier conditions. To our knowledge, this is the first study to determine the driving factors behind cyanobacterial activity in this region of the world. Our findings will help to predict and monitor areas at risk of future severe cyanobacterial blooms in the Okavango Delta and other similar African ecosystems.

Drought metrics and temperature extremes over the Okavango River basin, southern Africa, and links with the Botswana high

AbstractThe Okavango River Basin (ORB), including the World Heritage site Okavango Delta, is a region of high biodiversity projected to suffer increased early summer drying under climate change. Little work has been done on drought over this sensitive region. Here, various drought metrics are analysed over the ORB. These include a cumulative drought intensity index, based on the product of maximum temperature anomaly and maximum duration of a dry spell, and the Standardized Precipitation‐Evapotranspiration Index. Strong gradients in dry spell and hot day frequencies shift south over the ORB from August to November as the tropical rain‐belt moves increasingly south of the equator, the Congo Air Boundary declines and the Botswana High strengthens and moves southwestwards. By December, the tropical gradient in dry spell frequencies has vanished while that across the Limpopo River and southern ORB region, where the Botswana High is centred, is prominent. sub‐seasonal analyses highlight October–November 2013–2021 as particularly dry and hot over the Okavango Delta region. This dry and hot epoch appears related to a stronger and southward shifted Botswana High and reduced low‐level moisture convergence. On interannual scales, strong relationships were found with the Botswana High and El Niño‐Southern Oscillation (ENSO). The early summer shows a strong drying‐warming trend, related to a significant strengthening of the Botswana High. These trends, together with the Coupled Model Intercomparison Project Phase 6 projected early summer drying over southern Africa, may impact severely on the sensitive ecosystems of the ORB and on agriculture, with important implications for the management of agricultural activities, water resources and biodiversity.

Extreme rainfall events over the Okavango river basin, southern Africa

Characteristics of extreme rainfall events in the highly biodiverse Okavango River Basin (ORB) in west central southern Africa are not well understood. Hence, this study analyses the frequencies, intensities, spatial distributions, variability and trends of extreme rainfall events for the main rainy season, January–April (JFMA). The events are accumulated over 1-day (DP1) and 3-days (DP3). To identify these events, a method that accounts for both event intensity and spatial extent is used. On average, DP1 (DP3) events contribute ∼10% (∼17%) rainfall totals but in some years their contributions exceed 30%. Tropical-extratropical cloud bands are responsible for most of the events with tropical lows also important. The considerable interannual variability in extreme events appears related to El Niño-Southern Oscillation (ENSO) and the Botswana High.Although ENSO influences the extreme events as well as rainfall totals more generally over southern Africa, by far the wettest season over the iconic Okavango Delta region, in Ngamiland, Botswana, occurred during neutral JFMA 2017. These heavy rains resulted from a deeper Angola Low, weaker mid-level Botswana High which favoured convection in the region together with anomalous westerly moisture fluxes from the tropical South East Atlantic and enhanced low level moisture convergence over most of the region during January-early March. A dry period from mid-March was broken by the second most intense rainfall event on April 22nd, resulting from a cut-off low.Significant increasing trends were found in DP1 frequencies, as well as in rain-days and rain totals over many areas. These trends have important implications for water and agricultural management, and wildlife conservation in the highly biodiverse ORB.

Community Knowledge, Perceptions and Experiences on Healthcare Services for Malaria Prevention and Treatment in the Okavango Delta, Botswana.

This paper analyses community knowledge, perceptions, and experiences of effectiveness of healthcare service provision on malaria prevention/treatment in two disease-endemic villages of the Okavango Delta panhandle in northern Botswana. A stratified random sampling of 355 households was conducted in October-November 2015. Follow-up retrospective cohort interviews were undertaken in August 2016 from 79 households that reported malaria incidences during the household survey. Data were also collected from 16 key informant interviews and 2 focus group discussions participants. Descriptive statistics and content analyses were used to summarise quantitative and qualitative data, respectively. Results indicate that communities in the study sites had positive perceptions about efficiency of health services based on availability, accessibility and utilization, adequacy of prevention and treatment interventions. Local health clinics were crucial information channels used by respondents. Additionally, factors related to acceptability, availability and accessibility are likely to contribute to perceived effectiveness of the interventions provided by healthcare service providers. Affirmation of efficiency health service provision against malaria has public health implications for adherence to treatment/prevention and participation in community health education campaigns and program implementation in the Okavango Delta region.

Exceptional landscape-wide cyanobacteria bloom in Okavango Delta, Botswana in 2020 coincided with a mass elephant die-off event

In 2020, nearly 400 elephants died within the Okavango Delta region in Botswana, creating the worst-ever elephant mass die-off event in history. This catastrophic event was widely blamed on toxic cyanobacterial blooms after lab results showed the presence of toxin-forming cyanobacteria in inland waters of the Delta. However, it did not explain why we saw this mass die-off of elephants in 2020 and not in previous years. We conducted a landscape-wide time-series analysis using freely available European Space Agency's Sentinel-2 and NASA's Landsat-8 satellite data. We used existing bio-optical models, Normalized Difference Chlorophyll Index and Green Line Height, as proxies for chlorophyll-a and phycocyanin (cyanobacteria) concentrations. We found that 2020 was an exceptional year for cyanobacteria blooms in the Okavango Delta region compared to the past three years (2017–2019). Bloom phenology indicated that the cyanobacteria blooms initiated in September-October 2019, experienced an exponential growth reaching peak in January-February 2020, and eventually senescing in June 2020. This being a notoriously data-scarce region of the world, we did not have any means to perform site-specific validation of the models. Although magnitude and timeline of the blooms coincided with the timeline of elephant death reports, our study do not confirm it to be the trigger. For the first time, we show the widespread nature of these blooms across the landscape, which may have increased the toxin exposure for elephants. We theorize that 2020 might have been the first year for such a mass die-off event, but it will certainly not be the last because warming trends under changing climate are creating increasingly suitable conditions for these blooms to be pervasive and ubiquitous. Through this preliminary study, we demonstrate the critical need for frequent and comprehensive monitoring of toxic cyanobacterial blooms in the Delta to avoid another such event in the future.

Seroprevalence of viral and vector-borne bacterial pathogens in domestic dogs (Canis familiaris) in northern Botswana.

Domestic dogs (Canis familiaris) have the potential to act as disease reservoirs for wildlife and are important sentinels for common circulating pathogens. Therefore, the infectious disease seroprevalence among domestic dogs in northern Botswana may be indicative of pathogen exposure of various wildlife species. The objective of this study was to assess the seroprevalence of Ehrlichia spp., Borrelia burgdorferi, Anaplasma spp., Dirofilaria immitis, canine adenovirus, canine parvovirus, and canine distemper virus in domestic dogs as proxies of disease prevalence in the local wildlife in the Okavango Delta region of Botswana. Statistical analysis assessed crude and factor-specific seroprevalence proportions in relation to age, sex, and geographical location as predictors of seropositivity. Logistic regression was used to identify adjusted predictors of seropositivity for each of the pathogens of interest. Samples from 233 dogs in a total of seven locations in Maun, Botswana, and surrounding villages were collected and serologically analyzed. No dogs were seropositive for B. burgdorferi, while low seroprevalence proportions were observed for Anaplasma spp. (2.2%) and D. immitis (0.9%). Higher seroprevalence proportions were observed for the tick-borne pathogen Ehrlichia spp. (21.0%), and 19.7% were seropositive for canine adenovirus (hepatitis). The highest seroprevalence proportions were for canine parvovirus (70.0%) and canine distemper virus (44.8%). The predictors of seropositivity revealed that adults were more likely to be seropositive for canine adenovirus, canine distemper virus, and canine parvovirus than juveniles, and location was a risk factor for canine adenovirus, canine distemper virus, canine parvovirus, and Ehrlichia spp. Results indicate that increasing tick control and vaccination campaigns for domestic dogs may improve the health of domestic animals, and potentially wildlife and humans in the Okavango Delta since viral and vector-borne bacterial pathogens can be transmitted between them.

Effects of climate change on evapotranspiration over the Okavango Delta water resources

In semi-arid developing countries, most poor people depend on contaminated surface or groundwater resources since they do not have access to safe and centrally supplied water. These water resources are threatened by several factors that include high evapotranspiration rates. In the Okavango Delta region in the north-western Botswana, communities facing insufficient centrally supplied water rely mainly on the surface water resources of the Delta. The Delta loses about 98% of its water through evapotranspiration. However, the 2% remaining water rescues the communities facing insufficient water from the main stream water supply. To understand the effects of climate change on evapotranspiration over the Okavango Delta water resources, this study analysed trends in the main climatic parameters needed as input variables in evapotranspiration models. The Mann Kendall test was used in the analysis. Trend analysis is crucial since it reveals the direction of trends in the climatic parameters, which is helpful in determining the effects of climate change on evapotranspiration. The main climatic parameters required as input variables in evapotranspiration models that were of interest in this study were wind speeds, solar radiation and relative humidity. Very little research has been conducted on these climatic parameters in the Okavango Delta region. The conducted trend analysis was more on wind speeds, which had relatively longer data records than the other two climatic parameters of interest. Generally, statistically significant increasing trends have been found, which suggests that climate change is likely to further increase evapotranspiration over the Okavango Delta water resources.

On the effects of wildfires on precipitation in Southern Africa

This study investigates the impact of wildfire on the climate of Southern Africa. Moderate resolution imaging spectroradiometer derived burned area fraction data was implemented in a set of simulations to assess primarily the role of wildfire-induced surface changes on monthly precipitation. Two post-fire scenarios are examined namely non-recovering and recovering vegetation scenarios. In the former, burned vegetation fraction remains burned until the end of the simulations, whereas in the latter it is allowed to regrow following a recovery period. Control simulations revealed that the model can dependably capture the monthly precipitation and surface temperature averages in Southern Africa thus providing a reasonable basis against which to assess the impacts of wildfire. In general, both wildfire scenarios have a negative impact on springtime precipitation. September and October were the only months with statistically significant precipitation changes. During these months, precipitation in the region decreases by approximately 13 and 9% in the non-recovering vegetation scenario, and by about 10 and 6% in the recovering vegetation wildfire scenario, respectively. The primary cause of precipitation deficit is the decrease in evapotranspiration resulting from a reduction in surface net radiation. Areas impacted by the precipitation reduction includes the Luanda, Kinshasa, and Brazzaville metropolitan areas, The Angolan Highlands, which are the source of the Okavango Rive, and the Okavango Delta region. This study suggests that a probable intensification in wildfire frequency and extent resulting from projected population increase and global warming in Southern Africa could potentially exacerbate the impacts of wildfires in the region’s seasonal precipitation.

OSL dating of a carbonate island in the Chobe Enclave, NW Botswana

Abstract Carbonate platform islands are important landscape features in the northeastern part of the Okavango Delta region of Botswana, the Chobe Enclave. However, the formation processes and the timing of these “Chobe Islands” remain unclear. They are assumed to be the result of late Quaternary hydrological changes. Records of such changes are poorly preserved, though the occurrence of beach ridges in the Middle Kalahari Basin attests to the existence of large paleo-lakes in the past. Carbonate rocks from the Chobe Island appear to be relics of palustrine environments, but their relationship with the other hydrological archives is still unclear. Here, we report optically stimulated luminescence dating of key sedimentary beds in and around a single Chobe Island. It was necessary to model dose rate evolution for each sample individually, taking into account post-depositional changes in the sediment chemistry and its burial depth. The resulting ages suggest that the dated units were deposited between MIS6 to MIS1. The carbonate platform itself appears to have been deposited in two phases, separated by either an unexpectedly long (∼40 ka) depositional hiatus or an episode of erosion. This study demonstrates the potential of using luminescence dating in such settings, and offers the possibility of linking sedimentary processes within the Chobe Enclave to regional paleo-hydrological records.

Seismicity Study of Botswana from 1966 to 2012

The history of Botswana’s major seismic events has been initiated by two earthquakes that occurred on the 11th of September and 11th of October 1952 with ML Richter magnitudes of 6.1 and 6.7, respectively, in the Okavango Delta Region (ODR). Not much is known and well documented about the seismicity of a larger coverage of Botswana primarily because over the years, local seismic stations were biased to the north-western part of Botswana, to monitor the more seismogenic ODR. The objective of this study is to use data from the International Seismological Centre (ISC) bulletin for the period 1966-2012 to estimate the relative size distribution of seismic events (b-value), the rate of seismic activity (a-value), and associated stress condition prevailing in Botswana to assist in the quest of hazard mitigation. This study shows that micro-seismic activities of magnitude ranging from 1.3 to 5.7 are distributed not only on the northern part of Botswana, but also in other parts of the country such as the Southern (including Kweneng East and West), Central and Eastern Botswana. Based on 327 events extracted from data compiled by the ISC, the frequency-magnitude distribution (FMD) of earthquakes in Botswana from 1966 to 2012 was estimated with b-value and a-value for the entire catalogue found to be 1.2 and 6.3, respectively, implying a region of low stress dominated by small to moderate events. The minimum completeness magnitude (MC), a value that indicates the lowest magnitude above which all seismic events are reliably recorded was found to be 3.8. From this analysis, annual probabilities of occurrence for M4 and M5 events were found to be 67.2% and 4.3%, respectively, while M6 or larger event has an annual probability of 0.3%.

Symbiotic performance of grain and wild herbaceous legumes in the Okavango Delta and Tswapong region of Botswana

The low inherent soil fertility, especially nitrogen (N) constrains arable agriculture in Botswana. Nitrogen is usually added to soil through inorganic fertilizer application. In this study, biological nitrogen fixation by legumes is explored as an alternative source of N. The objectives of this study were to measure levels of N2 fixation by grain legumes such as cowpea, Bambara groundnut and groundnut in farmers’ fields as well as to estimated N2 fixation by indigenous herbaceous legumes growing in the Okavango Delta. Four flowering plants per species were sampled from the panhandle part of the Okavango Delta and Tswapong area. Nitrogen fixation was measured using the 15N stable isotope natural abundance technique. The δ15N values of indigenous herbaceous legumes indicated that they fixed N2 (−1.88 to +1.35 ‰) with the lowest value measured in Chamaecrista absus growing in Ngarange (Okavango Delta). The δ15N values of grain legumes growing on farmers’ fields ranging from −1.2 ‰ to +3.3 ‰ indicated that they were fixing N2. For grain legumes growing at most farms, %Ndfa were above 50% indicating that they largely depended on symbiotic fixation for their N nutrition. With optimal planting density, Bambara groundnuts on farmers’ fields could potentially fix over 90 kg N/ha in some parts of Tswapong area and about 60 kg N/ha in areas around the Okavango Delta. Results from this study have shown that herbaceous indigenous legumes and cultivated legumes play an important role in the cycling of N in the soil. It has also been shown that biological N2 on farmer’s field could potentially supply the much needed N for the legumes and the subsequent cereal crops if plant densities are optimized with the potential to increase food security and mitigate climate change.

Web Mapping for Promoting Interaction and Collaboration in Community Land Planning

Abstract. There is an inherent advantage of geographic information Systems (GIS) and mapping in facilitating dialogue between experts and non-experts during land use plan development. Combining visual mapping information and effective user interaction can result in considerable benefits for developing countries like Botswana. Although the adoption of information and communication technologies has lagged behind that for developed countries, initiatives by the Botswana government in providing suitable information infrastructures, including internet and web based communications, are enabling multiple users to interact and collaborate in community land planning. A web mapping application was developed for the Maun Development Plan (MDP) in the Okavango Delta region in Botswana. It was designed according to requirements of land planners and managers and implemented using ArcGIS Viewer for Flex. Land planners and managers from two organisations in Maun involved in the development of the MDP were asked to evaluate the web mapping tools. This paper describes the results of implementation and some preliminary results of the web mapping evaluation.

Resource use and the nutritional status of sable antelope in the Okavango Delta region of northern Botswana

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Tourism Impacts on Subsistence Agriculture: A Case Study of the Okavango Delta, Botswana

The booming tourism industry in the developing countries has been widely viewed as a source of investment, employment and foreign exchange. There is an assumption that the economic benefits of tourism will trickle down to stimulate other sectors of the economy, including agriculture. The government of Botswana, for example, is grappling with the task of developing a tourism policy that will maximize its goals of rural job creation, revenue generation from foreign exchange, conserve and protect wildlife, and be compatible with the cultural norms of its people. As the rural community in the Okavango Delta shifts its focus from agriculture to tourism, several concerns emerge. A key contention of this paper is that a major challenge facing the Okavango Delta region in the twenty first century is an attempt to support the tourism industry without compromising the traditional livelihoods of its local inhabitants. More specifically, as tourism increases economic growth and employment opportunities, it is becoming difficult for local inhabitants to sustain traditional subsistence agricultural livelihoods. As increasing numbers of rural, communal agricultural people migrate to urban areas, the International Union for the Conservation of Nature warned that the uncontrolled expansion of human activities, predominantly associated with tourism, and the foreign control of resources is resulting in the abandonment of many traditional practices, including agriculture, and threatening the livelihoods of the Okavango Delta's inhabitants. Hence, the Okavango Delta presents a unique opportunity to study the impact of tourism on rural agriculture, to observe the negotiation and competition which occurs between global tourism and local agriculture, and to review the inevitable transformation of local culture, economy and physical landscape.

Botswanan Palm Basketry among the Wounaan of Western Colombia: Lessons from an Intercontinental Technology Transfer

Traditional palm basketry of the Ba Yei and HaMbukushu people of the Okavango delta region in Botswana was introduced in the 1970s by a missionary to the Wounaan aborigines of western Colombia, who had a related weaving technique. The African technique was quickly assimilated by the Wounaan and enriched with shapes and decoration based on their own cultural patterns. The Chocoan palm Astrocaryum standleyanum, which the Wounaan used in their traditional baskets, replaced the African Hyphaene petersiana used in Botswana. The high quality of the new basketry led to a rapid success and turned Wounaan Astrocaryum baskets into an icon among Colombian handicrafts. Market pressure led to a severe depletion of the fiber-producing palm near Indian villages in the late twentieth century, as palms were felled by the hundreds to harvest the spear leaves. Educational campaigns and the introduction of an appropriate harvest tool have subsequently reduced the impact of leaf harvest, and A. standleyanum is now protected by the Wounaan. This case pinpoints the importance of a careful resource management assessment before introducing new market pressures on a traditional plant product. It is also a good example of positive results from a sustained campaign for appropriate resource management.

The Future of Traditional Customary Uses of Wildlife in Modern Africa: A Case Study of Kenya and Botswana

This paper discusses the future of traditional customary uses of wildlife in Africa. The continent’s wildlife is as old as humanity or perhaps even older. Indeed wildlife has through the ages remained a valuable resource for the African society; both in its traditional setting and in its modern form. While wildlife has some conventional and universal uses to society, there are some uses that are anthropologically unique to the African traditional way of life and therefore warrant special consideration. Such uses, for instance, manifest the inextricable attachment of the African peoples to the continent’s wildlife. Indeed there is a crucial link between wildlife and many traditional African cultural values and practices. One way in which these values manifest themselves is through the traditional customary uses of wildlife by the people. These uses are consumptive in nature and largely geared towards meeting the basic needs of humankind such as food, health and clothing. Research for this study was conducted in the Laikipia region of Kenya and the Okavango Delta region of Botswana. Information was obtained by the use of semistructured interviews, self-administered questionnaires, focus group discussions, and literature survey. The respondents included government officials, NGOs, experts as well as local communities. A total of 44 respondents were interviewed from each country, comprising households from the local communities within wildlife areas, senior ranking government officials, leaders of NGOs that actually work on wildlife issues, experts in natural resource management as well as eminent scholars in environmental and natural resources law and policy. The study established that these traditional uses continue to be either relegated by modern (or rather Western) way of life especially Christianity or restricted by the laws that are fashioned on American and European perceptions. This state of affairs has been largely engendered by western values as a result of colonialism, modern lifestyles as well as religious transformation from traditional African religions to Islam, Christianity and other present day religions. Admittedly, traditional wildlife uses are not necessarily undesirable and there is need for them to be recognized and promoted by the existing policies and laws. The paper recommends that African governments should, through their policies and laws, recognize and promote these traditional uses of wildlife. This is one way of ensuring that wildlife contributes to the day to day life of the people. It is only when this is achieved that the people of this needy continent of Africa will begin to appreciate the value of wildlife as a valuable resource to the present and future generations. Notably, the value of wildlife in western societies differs radically from its value in the traditional African context. While in western societies the importance of wildlife is perceived from its intrinsic value, in the traditional African context it is perceived from its direct uses—consumptive uses.

Wildlife Damage and its Impact on Public Attitudes Towards Conservation: A Comparative Study of Kenya and Botswana, with Particular Reference to Kenya’s Laikipia Region and Botswana’s Okavango Delta Region

While wildlife is a valuable natural resource with several beneficial values to the people of Kenya and Botswana, wild animals in both countries usually cause damage to society in terms of attacks on people and livestock, damage to crops and other property such as infrastructure, and disruption of peaceful existence in local communities living in close proximity to wildlife areas. Wildlife damage would ordinarily result in people having negative attitudes towards conservation. Interestingly, however, people’s perceptions of wildlife in these countries seem to be diametrically different in that whereas public attitudes in Kenya are generally negative, in Botswana they are remarkably positive. This study set out to establish the reasons for this variance in conservation attitudes. It established that the major cause for this variance in perception is that while in Kenya wildlife conservation is more often thought of in terms of wildlife welfare and hardly in terms of human welfare, in Botswana human welfare concerns have been mainstreamed in conservation efforts. People have, for instance, been allowed to derive direct benefits from wildlife through consumptive utilization, unlike in Kenya where only indirect benefits through non-consumptive uses are permitted. These direct benefits seem to mitigate the effects of wildlife damage, especially the resultant negative attitudes of people towards wildlife. The present and future survival of wildlife in many parts of the world, and especially in African countries such as Kenya and Botswana, depends to a large measure on the goodwill of the people, particularly local communities, in their everyday contact with it.

Foraging and distribution patterns in a termite assemblage dominated by fungus-growing species in semi-arid northern Botswana

Termite foraging was monitored with cellulose baits in both the wet and dry season in the semi-arid Okavango Delta region of northern Botswana. Seven wood-feeding species were found. Fungus-growing termites dominated the assemblage in all plots, and four species (Macrotermes michaelseni, Odontotermes sp. A, Allodontermes sp. and Microtermes sp.) were found in most. Foraging by smaller-bodied Allodontermes sp. and Microtermes sp. was largely confined to the wet season. Foraging by M. michaelseni and Odontotermes sp. A was more constant, but showed a general peak in the early dry season (May and June), likely due to nutrient and energy demands associated with alate production. Despite extensive overlap in distributions of these species, co-occurrences on baits were significantly less frequent than expected by chance. In addition, incidence in a plot of Allodontermes sp. and Microtermes sp. was negatively correlated in the wet season, as was that of M. michaelseni and Odontotermes sp. A in the dry season. Differences in body size, life history, and nest structure produce temporal and spatial heterogeneity in the foraging and distribution patterns of termites, and therefore suggest that consideration of community composition can improve prediction of the influence of termite assemblages on decomposition.

DECOMPOSITION RATES AND TERMITE ASSEMBLAGE COMPOSITION IN SEMIARID AFRICA

Outside of the humid tropics, abiotic factors are generally considered the dominant regulators of decomposition, and biotic influences are frequently not considered in predicting decomposition rates. In this study, I examined the effect of termite assemblage composition and abundance on decomposition of wood litter of an indigenous species (Croton megalobotrys) in five terrestrial habitats of the highly seasonal semiarid Okavango Delta region of northern Botswana, to determine whether natural variation in decomposer community composition and abundance influences decomposition rates. I conducted the study in two areas, Xudum and Santawani, with the Xudum study preceding the Santawani study. I assessed termite assemblage composition and abundance using a grid of survey baits (rolls of toilet paper) placed on the soil surface and checked 2–4 times/month. I placed a billet (a section of wood litter) next to each survey bait and measured decomposition in a plot by averaging the mass loss of its billets. Decomp...

Fish trypanosomes from the Okavango Delta, Botswana

During 2001 and 2002, blood smears from 37 of 120 fishes belonging to 10 species captured in the Okavango Delta region of Botswana, were found to harbour trypanosomes. These trypanosomes displayed differing staining properties, were morphometrically variable, and ranged in total length from 29.5 to 80.8 microm. Mixed populations of the smaller and larger trypanosomes were found in most fish examined. Despite variations in size and appearance, these specimens are tentatively identified as Trypanosoma mukasai Hoare, 1932, likely adding another 9 new hosts to those known for this parasite. It is possible that Trypanosoma clariense Pienaar, 1962, described from Clarias gariepinus in South Africa, is also a junior synonym of T. mukasai.