Spatial foraging patterns of the African honey bee,Apis mellifera scutellata

Recruitment patterns were investigated for the African honey bee in the Okavango River Delta, Botswana. The waggle dances of two observation colonies maintained in the field were monitored and used to construct maps of daily recruitment activity. These maps revealed that the African colonies frequently adjusted the allocation of recruits among food patches, recruited for 16–17 different food sites/day over areas of 55–80 km ² ,and concentrated the majority of recruitment within 1 km of the hives (median foraging distances for the two colonies were 295 and 563 m). In both colonies pollen foragers were more abundant than nectar foragers, and pollen sources indicated by waggle dancers were significantly closer to the hives than nectar sources. Compared to the recruitment patterns of temperate climate colonies, the African colonies had smaller recruitment areas, smaller mean recruitment distances, and a greater emphasis on pollen foraging. These differences may be related to the contrasting survival strategies followed by tropical-versus temperate-climate honey bees.     

The reproductive biology and early development of the African pike,Hepsetus odoe,in the Okavango Delta,Botswana

Synopsis The reproductive biology of the African pike,Hepsetus odoe, was studied over a four-year period in the Okavango Delta, Botswana. Spawning takes place between August and May in different parts of the Delta. Fish in the seasonal swamp and drainage rivers have a truncated spawning season between August and January, while those in the perennial swamp have an extended spawning season from September to May. The variation in spawning season appears to be associated with the degree of environmental perturbation brought about by the annual flood cycle. Male and female pike mature at 140 and 160 mm standard length (SL) respectively. Females predominate in the population and produce an average of 6440 eggs per season and are multiple spawners. The number of eggs per spawning averages about 2630. The eggs are deposited in a foam nest which is guarded by the parents. Newly hatched embryos suspend themselves below the nest via a cement gland and remain in the vicinity of the spawning site until they have reached a relatively advanced stage in their development. The larval period is relatively short which implies that this species undergoes nearly a direct development. Foam nests appear to be a predator avoidance mechanism as well as an adaptation to fluctuating oxygen and water levels. The initiation of the spawning season is more closely associated with water temperature than with the annual flood cycle which appears to be more important in regulating the size of the spawning stock.     

Seasonal patterns of foraging activity in colonies of the African honey bee,Apis mellifera scutellata,in Africa

Summary Seasonal foraging patterns were investigated using six observation colonies maintained in the Okavango Delta, Botswana. Pollen collection, flight from the hive, and recruitment for pollen and nectar sources occurred throughout the 11 months of the study. However, the distribution of foraging activity throughout the day changed seasonally. Colonies emphasized recruitment for pollen sites throughout most of the year. Brood production occurred in all months except May, and there was a significant, positive correlation between the proportion of recruitment activity devoted to pollen sources and the amount of brood comb in the colonies. The seasonal foraging patterns ofscutellata in the Okavango were similar to those of Africanized honey bees in the neotropics. The extended foraging season and emphasis on pollen collection may be associated with the high swarming rates and migrational movements of tropical honey bees.     

Nest characteristics and recruitment behavior of absconding colonies of the African honey bee,Apis mellifera scutellata,in Africa

Absconding behavior was investigated in a naturally occurring population of honey bees in the Okavango River Delta, Botswana. Fifty percent of all colonies excavated in the field between October and December had abandoned the nest or were preparing for absconding, suggesting that an absconding season began in the Delta in October or November. However, the factors influencing absconding during this period were unclear, and there were no distinct differences in nest characteristics of the absconding and nonabsconding colonies. Waggle dance activity in observation colonies preparing for absconding was not used to preselect a specific nest site prior to departure. However, in two of the three colonies examined recruitment activity indicated the general direction of colony travel. The distances indicated by these dancers ranged between 6 and 16 km. Since these distances were three to four times greater than those communicated by dancers in nonabsconding colonies, workers from absconding colonies may sample potential forage or nest sites well outside their regular foraging range.     

Factors influencing seasonal absconding in colonies of the African honey bee,Apis mellifera scutellata

Summary This study investigated the effects of colony growth and development, food storage, foraging activity and weather on the migration behavior of African honey bees in the Okavango River Delta, Botswana. Four observation colonies were studied during the honey bee migration season (November–May), at which time the availability of blooming species was reduced. Two of the colonies (colonies 1 & 2) migrated during the study period, while the remaining two (colonies 3 & 4) did not. During the 4–6 weeks preceding the onset of migration preparations, colonies 1 & 2 exhibited increasing population sizes, high levels of brood production with low brood mortality, relatively large stores of food, and increasing mass. In contrast, the populations of colonies 3 & 4 did not increase, brood-rearing activity was erratic and lower, brood mortality was higher, food stores became depleted and colony mass declined. Both colonies 3 & 4 ceased rearing brood, and colony 3 died of starvation. Colony foraging activity was examined by monitoring waggle-dance activity 2–3 days each week. For 4–6 weeks before the onset of migration in colonies 1 & 2, daily foraging areas and mean daily foraging distances became increasingly large and variable. Colonies 3 & 4 exhibited foraging patterns similar to those observed for colonies 1 & 2 preceding migration. There was no clear association between 7 weather parameters examined and migration behavior. These data suggest that migration is influenced by an interaction of intra-colony demographics, food reserves and foraging patterns. Migration may be feasible only for those colonies that possess (1) a population of appropriate size and age structure to compensate for the natural attrition of older workers during the emigration process, and (2) sufficient food reserves for long-distance travel and the establishment of a new nest. Changing foraging patterns may reflect a deteriorating foraging environment, which may trigger the onset of migration preparations, provided that colony demographics and food reserves are conducive. Colonies that show decreased brood production, higher brood mortality and reduced food stores may be incapable of migrating, even when experiencing deteriorating foraging conditions. Rather, such colonies may have a greater chance of survival if they attempt to persist in a given area.     

Major ion chemistry of the lower Boro River, Okavango Delta, Botswana

SUMMARY. 1. The composition of surface waters of the Boro River, Okavango Delta, Botswana, was determined on five occasions during 1989–1990. The waters could be characterized as caicium—sodium—bicarbonate, with moderate alkalinity, and moderate to high amounts of silica. Mean values of the major ions, in mg1-⁻¹, were: Ca²⁺ 4.8, Mg²⁺ 1.3, Na⁺ 3.9, K⁺ 2.7, HCO₃⁻ 27, Cl⁻ 1.0 and SiO₂ 38; pH c. 7.
2. The relative ionic composition of the waters changed gradually from the inlet in Seronga to the outlet at Boro/Thamalakane junction. There was a gradient of increasing concentrations of solutes resulting from the evaporative concentration of the waters in this semi-arid region with an almost permanent water deficit, and the total dissolved solutes increased from c. 30 to 95 mg 1-⁻¹
3. There were seasonal differences in solute concentrations, connected with the rainfall pattern and climatic cycle and an ill-defined relation with discharge. The chemical spectrum of the Boro, and the freshness of its waters, can be attributed to the major influence of precipitation within the basin and selective removal of solutes.
4. Chemical equilibrium models indicate that amorphous silica and sepiolite are likely to precipitate from the Boro waters. Carbonate and silicate systems are responsible for the selective removal of solutes in the swamps, islands, or flood plains, as proposed by others in recent studies, but not in the Boro River waters.     

Experiential Autochthony in the Okavango Delta,Botswana

The white Batswana of the Okavango identify as African, are strongly nationalistic and express deep senses of belonging to the social and physical environments of their birth and upbringing. Yet, claims to belonging by white people to extra-European territories are often perceived as inauthentic at best and neocolonial at worst. This raises the question of how the empirical realities of such connections can be analytically rendered without threatening or appropriating indigenous identities. Through making a case for the heuristic utility of the concept of experiential autochthony, I argue that emplacement and belonging can be fruitfully explored for migrant and settler groups.     

The reproductive and feeding biology of Schilbe intermedius Rüppell in the Okavango Delta,Botswana

The reproductive and feeding biology of 314 Schilbe intermedius Rüppell 1832 collected in the Okavango Delta, Botswana, between April 1985 and February 1986 during low, intermediate and high water level were investigated. S. intermedius matures at 130 mm standard length and is a monocyclic spawner. Females predominate in the population and have an average fecundity of 27107 eggs. In the northern riverine floodplain of the Delta fish spawn in mid-summer during the peak flood. In the southern drainage rivers fish spawn in spring, which is two to three months after the arrival of the winter flood waters. S. intermedius is an opportunistic predator with a diet consisting largely of fish 41%, aquatic larvae 25%, terrestrial insects 14%, aquatic insects 7% and crustacea 5%. Juvenile S. intermedius feed predominantly on insect larvae, while adults are largely piscivorous.     

Spatial foraging patterns and colony energy status in the African honey bee,Apis mellifera scutellata

The relationship between changes in foraging patterns (inferred from waggle dance activity) and colony energy status (inferred from brood rearing activity, food storage, and colony weight) was examined for the African honey bee during a period of relative resource abundance and resource dearth. When resources were more abundant mean foraging distances (about 400 m) and foraging areas (4–5 km²) were small, and colonies recruited to 12–19 different sites per day. Colony foraging ranges and sites visited increased slightly during the dearth period, yet foraging continued to be concentrated within less than 10 km². The degree to which fluctuations in foraging patterns were correlated with colony energy status varied with the availability of floral resources. During periods of relative forage abundance, increases in foraging range and number of sites visited were significantly correlated with increases in brood rearing and colony weight. In contrast, colonies examined during periods of resource dearth exhibited no correlations between foraging areas, foraging distances, and fluctuations in brood rearing, food storage, or colony weight. Thus, during dearth periods colonies may not be able to coordinate foraging patterns with changes in colony energy status.     

Land-use and resource conflicts in the Okavango Delta, Botswana

This study assesses land-use conflicts in the Okavango wetland ecosystem. A survey of the livelihood activities of a sample of four villages has been carried out and a stakeholder approach used to identify and analyse the key actors involved in resource competition and conflicts in the area. Traditional and emerging stakeholders were identified and found to be in conflict not only with each other but within themselves. Institutional policies on land use in the area are not properly harmonized, and there has been a top-down approach to development planning and implementation of development programmes. As a result, land-use conflicts have escalated in the area. The Okavango Delta Management Plan adopted in 2007 should integrate and harmonize all the land-use policies, and land management in the area.     

Spatial and temporal dynamics of diffusive methane emissions in the Okavango Delta,northern Botswana,Africa

Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH₄) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH₄ in the world contributing between 100 and 231 Tg year^?1 to the total budget of 503–610 Tg year^?1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH₄ emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH₄ emission rates varied between 0.24 and 293 mg CH₄ m^?2 h^?1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH₄ m^?2 h^?1 or 558 ± 53 mg CH₄ m^?2 day^?1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher (P < 0.007) in permanent than in seasonal swamps. River channels exhibited the highest average fluxes at 31.3 ± 5.4 mg CH₄ m^?2 h^?1 than in floodplains (20.4 ± 2.5 mg CH₄ m^?2 h^?1) and lagoons (16.9 ± 2.6 mg CH₄ m^?2 h^?1). Diffusive CH₄ emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH₄ m^?2 h^?1) and lowest (0.2–3.0 mg m^?2 h^?1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km², the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH₄ emission from global tropical wetlands.     

Surface water quality in the Okavango Delta panhandle,Botswana

The Okavango Delta, a Ramsar and a World Heritage Site, is an important source of food and water in the Kalahari Desert of southern Africa. Although the eastern delta fan is a protected area, the rest, including the upstream panhandle, is unprotected. Water quality in the Okavango Delta panhandle from Popa Falls, Namibia, to lagoons in the north-western delta fan, was investigated between December 2006 and January 2009. Results were compared to those of a study undertaken in the lower panhandle in the mid-1980s, in order to identify changes, if any. Despite increased human activities and livestock, physical water quality parameters lay within the ranges set out in the water quality guidelines of South Africa, while most chemical substances were below detection limits. The microbiological water quality indicated that microbial concentration was highest in areas of increased human and livestock activity. In general, the water quality of the unprotected panhandle had remained unaltered after more than two decades of change and growing pressure on it.     

Waggle dance behavior associated with seasonal absconding in colonies of the African honey bee,Apis mellifera scutellata

Summary Waggle dance activity associated with seasonal absconding (migration) was investigated in two colonies of the African honey bee. Prior to absconding, waggle dances regularly communicated distances up to 10–20 km from the nests. However, compared to waggle dances observed during nonabsconding periods, those occurring prior to migration were less associated with food sources, occurred during periods of little or no flight activity, and exhibited great variability in the communication of distance by consecutive waggle runs of individual bees. It is therefore unlikely that migration dances communicated the locations of, or stimulated immediate recruitment for, specific foraging or nesting sites. Rather, the dances may have functioned to establish a general route of travel. The majority of migration dances observed were oriented in an easterly direction, and upon departure both colonies traveled towards the E-SE. The orientation of migration dances occurred independently of the directions communicated by waggle dances associated with past foraging success or the sampling of alternate foraging areas. Migration dance orientation may have been affected by prevailing wind directions, because during the migration period winds blew primarily from the east. However, it is unlikely that wind direction was the only factor influencing migration dance orientation. The lack of immediate flight activity associated with migration dance performance suggests the dances may have gradually prepared colonies for migratory movement by conveying a message to fly for a long, but unspecified distance in a certain direction. Waggle dances associated with migration may therefore function differently from those associated with foraging and nest site selection, which convey both the distance and direction to specific locations.     

On some predatory nematodes from the Okavango Delta,Botswana

Five species of Mononchida and Mononchulus nodicaudatus (v. Daday, 1899) Cobb, 1918 are reported from freshwater sediments at or near Boba Island, Okavango Swamps, Botswana. Illustrations are given for Mylonchulus lacustris (Cobb N.A. in Cobb MX, 1915) Andrássy, 1958, Iotonchus risoceiae (Carvalho, 1955) Andrássy, 1958 and Cobbonchus spec. Two species of Mononchus Bastian, 1865, M. aquaticus Coetzee, 1968 and M. truncatus Bastian, 1865 were also found. The usually rare species M. nodicaudatus was well represented and its juvenile stages are described for the first time.     

Home range occupation and habitat use of sable antelope in the Okavango Delta region of northern Botswana

Animals selectively utilize their environments within a hierarchical framework. Our study addressed how the home ranges of sable antelope selectively incorporated the landscape and habitat types available to them. It was conducted in a region of northern Botswana where the sable population was expected to be thriving, in contrast to their threatened status in the wild in South Africa. The movements and habitat use of three neighbouring sable herds were recorded by global positioning system (GPS) telemetry during parts of the seasonal cycle in a region adjoining the seasonally flooded Okavango Delta. Total home range extents covered by these herds were larger than those found for sable in other areas, and local population densities, taking into account the herd sizes, were accordingly lower than in these other areas. Access to surface water appeared to be the main limitation on seasonal home range occupation. Almost all of the local vegetation types were utilized, but sable herds generally favoured dryland grassland during the dry season and floodplain grassland during the wet season, contrary to what we had expected. Hence, it appeared that local home range occupation and habitat use by the three sable antelope herds could be influenced more by interactions with potential competitors and predators than by intrinsic habitat suitability.     

Nutrient Budget in the Seasonal Wetland of the Okavango Delta, Botswana

The nutrient (P and N species) and chloride budgets were investigated in a representative floodplain in the seasonal wetlands of the Okavango Delta, Botswana. A variety of sources of nutrients in the surface water were considered, namely ion species coming with the floodwater, those generated from dry floodplain soils and those from water-soluble dust deposition (both local and long-range sources). Concentrations of total-nitrogen and chloride in surface water were below 1 mg l⁻¹. Total-phosphorus concentrations were 0.05 mg l⁻¹, reflecting the oligotrophic character of the system. Dust deposition rates were highest for chloride at 2.44 g m⁻² year⁻¹ followed by 0.79 g m⁻² year⁻¹ for total-N, 0.40 g m⁻² year⁻¹ for ammonia and only 0.02 g m⁻² year⁻¹ for total-P, respectively. Chloride was derived primarily from long-range transport, while N and P species were of more local origin. Dissolution rates for these ions combined were calculated to be 3.9 g m⁻² for the flooded area in the 1999 season and thus all dry deposits must be re-dissolved. The accumulation of dust deposits on dry surfaces and their subsequent dissolution causes 2–5 times higher concentrations of nitrogen, phosphorus and chloride with the onset of the flood, thus boosting the nutrient stock in the crucial phase of the onset of flooding. Chloride dissolved from dry soil surfaces and dust contributed approximately 40% to the overall floodplain budget. Although contributions from the soil surface and dust to the nitrogen and phosphorus pools of the floodplain are less prominent (with 10% of total), they nonetheless represent a significant source of nutrients in the entire system. Extrapolation to annually flooded swamps (10,000 km²) indicates a maximum contribution of 40% for total-nitrogen and 60% for total-phosphorus from dust deposition on wet or dry surfaces to the nutrient pool of the water body.     

Community ecology and conservation of the fishes of the Okavango Delta,Botswana

Synopsis The Okavango Delta is a large inland swamp in northern Botswana which receives an annual flood from the highlands of southern Angola. There are distinct fish taxocenes in the Okavango which can be separated from each other by the physical characteristics of the different habitat types with which they co-evolved. An account is given of the ecology and conservation of the fishes of the Okavango Delta. Their response to the annual flood regime, and the environmental factors that limit their distribution and abundance, are described. In the northern riverine floodplain and perennial swamp a higher species richness and ichthyomass was recorded than in the seasonal swamp and drainage rivers. Suggestions are made on the conservation of Okavango fishes taking into account the ecological characteristics of the Delta.     

Effects of a neonicotinoid pesticide on thermoregulation of African honey bees (Apis mellifera scutellata)

Thiamethoxam is a widely used neonicotinoid pesticide that, as agonist of the nicotinic acetylcholine receptors, has been shown to elicit a variety of sublethal effects in honey bees. However, information concerning neonicotinoid effects on honey bee thermoregulation is lacking. Thermoregulation is an essential ability for the honey bee that guarantees the success of foraging and many in-hive tasks, especially brood rearing. We tested the effects of acute exposure to thiamethoxam (0.2, 1, 2 ng/bee) on the thorax temperatures of foragers exposed to low (22 °C) and high (33 °C) temperature environments. Thiamethoxam significantly altered honey bee thorax temperature at all doses tested; the effects elicited varied depending on the environmental temperature and pesticide dose to which individuals were exposed. When bees were exposed to the high temperature environment, the high dose of thiamethoxam increased their thorax temperature 1–2 h after exposure. When bees were exposed to the low temperature, the higher doses of the neonicotinoid reduced bee thorax temperatures 60–90 min after treatment. In both experiments, the neonicotinoid decreased the temperature of bees the day following the exposure. After a cold shock (5 min at 4 °C), the two higher doses elicited a decrease of the thorax temperature, while the lower dose caused an increase, compared to the control. These alterations in thermoregulation caused by thiamethoxam may affect bee foraging activity and a variety of in-hive tasks, likely leading to negative consequences at the colony level. Our results shed light on sublethal effect of pesticides which our bees have to deal with.