Okavango River Delta Research Articles

RESPONSE OF RIPARIAN VEGETATION IN AUSTRALIA"S LARGEST RIVER BASIN TO INTER AND INTRA-ANNUAL CLIMATE VARIABILITY AND FLOODING AS QUANTIFIED WITH LANDSAT AND MODIS

Australia is a continent subject to high rainfall variability, which has major influences on runoff and vegetation dynamics. However, the resulting spatial-temporal pattern of flooding and its influence on riparian vegetation has not been quantified in a spatially explicit way. Here we focused on the floodplains of the entire Murray-Darling Basin (MDB), an area that covers over 1M km<sup>2</sup>, as a case study. The MDB is the country’s primary agricultural area with scarce water resources subject to competing demands and impacted by climate change and more recently by the Millennium Drought (1999–2009). Riparian vegetation in the MDB floodplain suffered extensive decline providing a dramatic degradation of riparian vegetation. <br><br> We quantified the spatial-temporal impact of rainfall, temperature and flooding patters on vegetation dynamics at the subcontinental to local scales and across inter to intra-annual time scales based on three decades of Landsat (25k images), Bureau of Meteorology data and one decade of MODIS data. <br><br> Vegetation response varied in space and time and with vegetation types, densities and location relative to areas frequently flooded. Vegetation degradation trends were observed over riparian forests and woodlands in areas where flooding regimes have changed to less frequent and smaller inundation extents. Conversely, herbaceous vegetation phenology followed primarily a ‘boom’ and ‘bust’ cycle, related to inter-annual rainfall variability. Spatial patters of vegetation degradation changed along the N-S rainfall gradient but flooding regimes and vegetation degradation patterns also varied at finer scale, highlighting the importance of a spatially explicit, internally consistent analysis and setting the stage for investigating further cross-scale relationships. <br><br> Results are of interest for land and water management decisions. The approach developed here can be applied to other areas globally such as the Nile river basin and Okavango River delta in Africa or the Mekong River Basin in Southeast Asia.

RESPONSE OF RIPARIAN VEGETATION IN AUSTRALIA"S LARGEST RIVER BASIN TO INTER AND INTRA-ANNUAL CLIMATE VARIABILITY AND FLOODING AS QUANTIFIED WITH LANDSAT AND MODIS

Abstract. Australia is a continent subject to high rainfall variability, which has major influences on runoff and vegetation dynamics. However, the resulting spatial-temporal pattern of flooding and its influence on riparian vegetation has not been quantified in a spatially explicit way. Here we focused on the floodplains of the entire Murray-Darling Basin (MDB), an area that covers over 1M km2, as a case study. The MDB is the country’s primary agricultural area with scarce water resources subject to competing demands and impacted by climate change and more recently by the Millennium Drought (1999–2009). Riparian vegetation in the MDB floodplain suffered extensive decline providing a dramatic degradation of riparian vegetation. We quantified the spatial-temporal impact of rainfall, temperature and flooding patters on vegetation dynamics at the subcontinental to local scales and across inter to intra-annual time scales based on three decades of Landsat (25k images), Bureau of Meteorology data and one decade of MODIS data. Vegetation response varied in space and time and with vegetation types, densities and location relative to areas frequently flooded. Vegetation degradation trends were observed over riparian forests and woodlands in areas where flooding regimes have changed to less frequent and smaller inundation extents. Conversely, herbaceous vegetation phenology followed primarily a ‘boom’ and ‘bust’ cycle, related to inter-annual rainfall variability. Spatial patters of vegetation degradation changed along the N-S rainfall gradient but flooding regimes and vegetation degradation patterns also varied at finer scale, highlighting the importance of a spatially explicit, internally consistent analysis and setting the stage for investigating further cross-scale relationships. Results are of interest for land and water management decisions. The approach developed here can be applied to other areas globally such as the Nile river basin and Okavango River delta in Africa or the Mekong River Basin in Southeast Asia.

Dynamics of the feeding ecology of selected fish species from the Okavango River delta, Botswana

Dynamics of the feeding ecology of selected fish species from the Okavango River delta, Botswana

Dynamics of the feeding ecology of selected fish species from the Okavango River delta, Botswana

Dynamics of the feeding ecology of selected fish species from the Okavango River delta, Botswana

Mental health in Botswana

Botswana is a landlocked country located in southern Africa. More than two-thirds of it (70%) is covered by the Kalahari Desert, known locally as the Kgalagadi. The majority (82%) of the nearly 2 million population live in the eastern part, along the railway line from Lobatse in the south-east to Francistown in the north-east, and the rest in the central part, including the Okavango River delta.

Seasonal and inter-annual photosynthetic response of representative C4 species to soil water content and leaf nitrogen concentration across a tropical seasonal floodplain

AbstractWe examined the seasonal and inter-annual variation of leaf-level photosynthetic characteristics of three C4 perennial species, Cyperus articulatus, Panicum repens and Imperata cylindrica, and their response to environmental variables, to determine comparative physiological responses of plants representing particular microhabitats within a seasonal tropical floodplain in the Okavango River Delta, Botswana. Five measurement campaigns were carried out over a period of 2 y which covered two early rainy seasons, two late rainy seasons and one dry season. For all three species, light-saturated net photosynthetic rates (Asat) and stomatal conductance (gsat) decreased with decreasing soil water content with a seasonal range for Asat of approximately 5–45 μmol m−2 s−1, and for gsat of 0.03–0.35 mol m−2 s−1. The species representing the wettest microhabitat (Cyperus) had the highest gsat at low leaf-to-air vapour pressure deficits (Dl), the highest ratio of intercellular to ambient CO2 concentration (Ci/Ca), as well as the highest degree of variation in Ci/Ca from season to season. We interpret this as being indicative of its adaptation to a moist growth environment allowing for non-conservative water use strategies as soil moisture is usually abundant. For all three species there was significant variation in photosynthetic fluxes from one year to another that was related to variation in leaf nitrogen and phosphorus. This study shows that when assessing the role of savanna stands in large-scale carbon balance models, the remarkable inter-annual variation in leaf photosynthesis reported in this study should be taken into account.

A preliminary survey and analysis of the spatial distribution of aquatic invertebrates in the Okavango Delta, Botswana

The spatial distribution of aquatic macroinvertebrates in the Okavango River Delta, Botswana, was investigated during the low-water period in February 2003. This complements an earlier study undertaken during high-water in June 2000. Seventy-five samples were taken in a range of aquatic habitats at 29 georeference points in four focal areas: Upper Panhandle (UPH), Lower Panhandle and Guma Lagoon (LPH), Moremi Game Reserve/Xakanaka (MGR), and Chief's Island (CI). Over 180 morphospecies (approximately 63 families) were recorded during the survey. Multivariate analyses of macroinvertebrate assemblages indicated that assemblages in each of the four focal areas were at least 54% similar at morphospecies level, and 71% similar at family level, although some taxa were more or less common in different areas. Differences in macroinvertebrate assemblages were observed amongst different habitat types, with differences most pronounced between the deltaic habitats and isolated seasonally-flooded pools and temporary rain-filled pools in MGR and CI. The highest number of taxa was recorded in the MGR (125), followed by the UPH (96), CI (93) and the LPH (89) areas. The most families were recorded in the Hemiptera (11), followed by Mollusca (10), Diptera (nine), Coleoptera (nine), Crustacea (six), Ephemeroptera (six) and Odonata (four). Three families of Hirudinea and Trichoptera, and one family of Lepidoptera, were also recorded. Hydracarina were common but not identified beyond order, while Oligochaeta were less frequently recorded. With respect to the different aquatic habitats sampled, the highest number of taxa was recorded in marginal vegetation in the channels and lagoons, although inundated floodplains, floating vegetation and marginal vegetation in backwaters also supported many taxa. The fewest taxa were recorded in sediment. This survey, whilst representing a 'snapshot' of the system under low-water conditions, highlights the importance of maintaining a mosaic of aquatic habitats in the Delta. Further studies would enhance our knowledge of the aquatic macroinvertebrate biodiversity of the Okavango Delta, thereby contributing to its conservation.

The World Crane Action Plan: implications for conservation of cranes and wetlands in Africa

Beilfuss, R.D., Meine, C.D., & Archibald, F.W. 2000. The World Crane Action Plan: implications for conservation of cranes and wetlands in Africa. Ostrich 71 (1 & 2): 227. The IUCN Species Survival Commission recently published The Cranes: Status Survey and Conservation Action Plan. Prepared over the past three years by the IUCN Crane Specialist Group, the document reviews the status of the world's cranes (Family: Gruidae) and their habitats, summarises recent crane conservation actions, and specifies priority measures for the future. Eleven of the 15 crane species are now proposed for inclusion on the IUCN Red List of Threatened Animals, and several subspecies and populations are critically endangered. Africa supports six species of cranes in 39 countries. The Black Crowned Crane Balearica pavonina, national bird of Nigeria, is resident in western and central Africa. The Grey Crowned Crane B. regulorum, national bird of Uganda, spans eastern and southern Africa. The Wattled Crane Bugeranus carunculahrs, largest and. rarest of Africa's cranes, ranges from Ethiopia to South Africa. The Blue Crane Anthropoides paradiseus, national bird of South Africa, is endemic to South Africa and Namibia. The Demoiselle Crane A. Virgo and Eurasian Crane Grus grus are winter visitors. Cranes have been the focus of intensive captive propagation and reintroduction programs as well as extensive habitat protection efforts. They are also excellent umbrella species for ecosystem-level conservation efforts. Wetlands that provide a home for cranes include the floodplains of the great river systems of Africa, such as Kafue Flats and Zambezi Delta of the Zambezi River system, the Okavango River Delta, the Sudd of the Upper Nile River, the Bangweulu Basin and swamps of the Zaire River system, the Senegal River Delta, and the Inner Niger River Delta, and the wetlands of Lake Chad. Small, isolated wetlands provide vital breeding habitat. This presentation will provide an overview of the action plan for those interested in cranes in particular, as well as those working in ecosystems and regions where cranes occur.

Spatial Distribution and Nesting Biology of Colonies of the African Honey Bee Apis mellifera scutellata (Hymenoptera: Apidae) in Botswana, Africa

The spatial distribution and nesting biology were examined for naturally occurring colonies of the African honey bee race Apis mellifera scutellata (Lepeletier) in the Okavango River Delta, Botswana. Colonies had a density of 4.2/km 2 but exhibited considerable spatial clumping. Nest aggregations did not appear to result from short swarm dispersal distances, clumped resources or benefits derived from increased nest defense. Nests occurred predominantly in wooden cavities, particularly in abandoned woodpecker nests in dead palm trees. Nest cavities had a volume of =33 liters and south-facing, top-located entrances. Colonies constructed =6,000 cm 2 of comb, devoted the majority of comb area to worker brood production, stored relatively little food, and allocated =8% of comb area to drone rearing. A comparison of the A. m. scutellata colonies in the Okavango with neotropical African colonies throughout Central and South America revealed that the neotropical colonies were more likely to construct exposed comb nests and less likely to occupy wooden cavities. However, no differences were found between the Okavango and neotropical colonies in nest density, cavity volume, total comb area, or the proportions of comb devoted to worker brood production, food storage or drone rearing. Thus, the aspects of nesting biology examined appear to have remained largely unchanged from the ancestral African condition during the colonization of Central and South America.

Developmental patterns associated with founding and swarming in colonies of the African honey bee race, Apis mellifera scutellata Lepeletier

The developmental patterns of naturally occurring, recently founded colonies of the African honey bee race, Apis mellifera scutellata, were examined in the Okavango River Delta, Botswana. Colonies moved into the study area beginning in mid-June. During the first 3-4 months after founding, colonies devoted most comb area to worker brood production, reared few or no drones, emphasized pollen collection, yet stored little food. Reproductive swarming occurred in October-November, at which time brood production declined, and food storage and drone production increased. Thus, the developmental strategy of newly founded colonies in the Okavango is geared towards rapid growth and the immediate channeling of harvested resources into worker brood, which culminates in a relatively brief period of reproductive swarming

Drone production and drone comb utilization in colonies of the African honey bee, Apis mellifera scutellata Lepeletier, in Africa

Drone production and drone comb utilization were investigated in naturally occurring colonies of the African honey bee, Apis mellifera scutellata, in the Okavango River Delta, Botswana. Drone production occurred primarily in larger, thriving and swarming colonies that contained large proportions of worker brood, and by inference were experiencing a period of growth. Drone production was rare( observed in smaller, newly established colonies, or larger colonies with reduced worker brood rearing. Maximum drone production occurred in September-October, and coincided with the swarming season and the period of peak resource abundance. Drone production occurred sporadically throughout the remainder of the year

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

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.

Colony Defense in the African Honey Bee in Africa (Hymenoptera: Apidae)

Defensive behavior was investigated in a naturally occurring population of Apis mellifera scutellata (Lepeletier) colonies in the Okavango River Delta, Botswana. In general, colonies exhibited low levels of stinging activity during nest dissection. However, positive associations were observed between defensiveness and increasing colony size (inferred from total comb area) and swarming activity. The lower stinging activity of the smaller colonies and the increased defensiveness of the larger and swarming colonies may have reflected relative levels of investment in colony growth and reproductive potential. Seasonal patterns of colony defensiveness were not associated with fluctuations in resource abundance, although some changes in forage availability may have influenced aggressive behavior. Colony defensiveness was not associated with nest entrance location and orientation; the proportions of comb area devoted to brood rearing, food storage, or the area that was empty, or any of three weather parameters measured.

Seasonal cycles of growth, development and movement of the African honey bee,Apis mellifera scutettata, in Africa

The relationship between the annual colony cycle and seasonal patterns of forage availability was investigated for the African honey bee,Apis mellifera scutellata, in the Okavango River Delta, Botswana. The annual cycle occurred in three distinct periods. The swarming season occurred from October-November, following two to three months of intense brood production, and coincided with the end of peak forage abundance. The migration season occurred from November-May and coincided with reduced and variable floral resources. During the migration season, brood production and food storage were generally low but quite variable from month to month, and swarms passing over the study area at this time traveled in an easterly direction. The migration season was followed by the establishment period (June-September), in which large numbers of new colonies traveling from the west moved into the study area. The establishment period coincided with, and slightly preceded, the period of peak forage abundance, and colonies devoted resources collected at this time almost entirely to brood rearing, which culminated in swarm production. The data suggest that honey bee colonies in the Okavango are mobile and gear their reproduction and movement to seasonally shifting resource pattern.

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.

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.

Dance Behaviour of Successful Foragers of the African Honeybee,Apis Mellifera Scutellata(Hymenoptera: Apidae)

SummaryVibration dance behaviour was monitored for foragers of the African honeybee in the Okavango River Delta, Botswana. Approximately 50% of successful foragers performed vibration dances within 5 min of entering the hive. Also, 30–40% of the foragers observed within a colony at any given time were vibrators. Since the vibration dance may enhance recruitment, vibrating foragers may play an important role in the regulation of foraging activity in African colonies.A new dance behaviour, the ‘buzz dance’, is described for African honeybees. While the function of the buzz dance was not determined, it was performed by successful foragers, frequently in conjunction with vibration and waggle dances. The buzz dance may therefore be associated with recruitment.

The habitat and nesting biology of the African honey beeApis mellifera scutellata in the Okavango River Delta, Botswana, Africa

The habitat and nesting biology were studied for naturally occurring colonies of the African honey bee,Apis mellifera scutellata, in the Okavango River Delta, Botswana. Vegetational surveys revealed that the forage available to Delta colonies was abundant and potentially available year round. Colonies had a density of 7.8 nests/km2. Nest cavities occurred with equal frequency in trees and termite mounds, had a volume of approximately 17 L, were unpropolized, and had south-facing, top-located entrances. Delta colonies were small (ca. 6,500 workers), constructed small amounts of comb (ca. 3,000 cm2), stored little food, devoted 78% of comb space to brood production, exhibited little nest defense, and experienced a 48% predation rate during the 5 month study period. The characteristics observed forscutellata in this study are discussed as adaptations to the hot climate, long foraging season, and high predation rate experienced in the Delta. Data for the Delta colonies are compared to those forscutellata in other tropical areas, and to honey bees in temperate climate regions.