Kalahari Research Articles

Exotic oryx interact with shrub encroachment in the Chihuahuan Desert

Biotic invasions can interact with ongoing landscape transitions in introduced ranges, acting synergistically to accelerate landscape change. The African oryx (Oryx gazella), a large ungulate native to the Kalahari Desert in southern Africa, was intentionally released into the Chihuahuan Desert of southern New Mexico to provide increased hunting opportunities. Oryx have subsequently dispersed widely, including into the adjacent Jornada Basin Long Term Ecological Research site, which contains native grassland communities imperiled due to shrub encroachment. We examined how landscape use and diel activity of oryx interacts with shrub encroachment at Jornada Basin. We hypothesized that oryx would be more common on unencroached grasslands that provide preferred forage, and that oryx would be most active at dawn and dusk (crepuscular) when ambient temperatures were favorable and predator surveillance was possible. We sampled 24 sites across a broad gradient of shrub encroachment from 2014 to 2018 using camera traps to evaluate our hypotheses. Oryx relative abundances were higher on unencroached grasslands, especially in years of low to moderate precipitation. We found oryx were most active during crepuscular periods, and this behavior was consistent across the shrub encroachment gradient. Our research suggests exotic oryx could contribute to shrub encroachment by focusing their foraging on remaining grasslands, especially during drier years, which may adversely affect livestock production and other ecosystem services.

Changing socio-ecologies of Kalahari: Local perceptions towards environmental change and tourism in Kgalagadi, Botswana

ABSTRACT Central parts of southern Africa are expected to face major environmental and economic changes in the near future, calling for proactive thinking on how local people could diversify their livelihoods. In Botswana, the tourism industry is considered as a major option for economic diversification and current tourism policies include a strong emphasis on tourism that participates in and benefits communities. The developmental impact of tourism depends on how the local communities perceive their livelihood options and the role of tourism. This paper analyses how community members in selected villages in Kalahari Desert perceive the current and estimated future impacts of climate change and how these impacts may influence their livelihoods in future and what role the tourism industry may play in that process. Based on the results, there are minimal local benefits and participation in tourism, which limits the potential of tourism to work for sustainable local development in practice.

Signalling adjustments to direct and indirect environmental effects on signal perception in meerkats.

The efficiency of communication between animals is determined by the perception range of signals. With changes in the environment, signal transmission between a sender and a receiver can be influenced both directly, where the signal's propagation quality itself is affected, and indirectly where the senders or receivers' behaviour is impaired, impacting for example the distance between them. Here we investigated how meerkats (Suricata suricatta) in the Kalahari Desert adjust to these challenges in the context of maintaining group cohesion through contact calls. We found that meerkats changed their calling rate when signal transmission was affected indirectly due to increased dispersion of group members as during a drought, but not under typical wet conditions, when signal transmission was directly affected due to higher vegetation density. Instead under these wetter conditions, meerkats remained within proximity to each other. Overall, both direct and indirect environmental effects on signal perception resulted in an increased probability of groups splitting. In conclusion, we provide evidence that social animals can flexibly adjust their vocal coordination behaviour to cope with direct and indirect effects of the environment on signal perception, but these adjustments have limitations.

The allelopathic, adhesive, hydrophobic and toxic latex of Euphorbia species is the cause of fairy circles investigated at several locations in Namibia

BackgroundIn this multidisciplinary study we present soil chemical, phytochemical and GIS spatial patterning evidence that fairy circles studied in three separate locations of Namibia may be caused by Euphorbia species.ResultsWe show that matrix sand coated with E. damarana latex resulted in faster water-infiltration rates. GC-MS analyses revealed that soil from fairy circles and from under decomposing E. damarana plants are very similar in phytochemistry. E. damarana and E. gummifera extracts have a detrimental effect on bacteria isolated from the rhizosphere of Stipagrostis uniplumis and inhibit grass seed germination. Several compounds previously identified with antimicrobial and phytotoxic activity were also identified in E. gummifera. GIS analyses showed that perimeter sizes and spatial characteristics (Voronoi tessellations, distance to nearest neighbour ratio, pair correlation function and L-function) of fairy circles are similar to those of fairy circles co-occurring with E. damarana (northern Namibia), and with E. gummifera (southern Namibia). Historical aerial imagery showed that in a population of 406 E. gummifera plants, 134 were replaced by fairy circles over a 50-year period. And finally, by integrating rainfall, altitude and landcover in a GIS-based site suitability model, we predict where fairy circles should occur. The model largely agreed with the distribution of three Euphorbia species and resulted in the discovery of new locations of fairy circles, in the far southeast of Namibia and part of the Kalahari Desert of South Africa.ConclusionsIt is proposed that the allelopathic, adhesive, hydrophobic and toxic latex of E. damarana, E. gummifera, and possibly other species like E. gregaria, is the cause of the fairy circles of Namibia in the areas investigated and possibly in all other areas as well.

The Plight of the Kalahari San: Hunter-Gatherers in a Globalized World

The San (Bushmen) of the Kalahari Desert of southern Africa have diversified livelihoods that are undergoing significant change. This article explores the complex challenges that San and their neighbors face, ranging from dispossession and social marginalization to climate change and the impacts of globalization. Some San have experienced involuntary resettlement from their ancestral areas because of the establishment of protected areas, agricultural projects, roads, and mines. Some have also had to deal with the criminalization of their livelihood strategies, notably hunting and gathering. Many San seek to promote their indigenous languages and cultural heritage in the face of imposed efforts to assimilate them in the countries where they reside. In recent years the San have achieved some success in organizing themselves both locally and internationally. Notably, they have filed legal cases aimed at regaining their land and resource rights in Botswana, Namibia, and South Africa.

13,000 years of sociocultural plant use in the Atacama Desert of northern Chile

Throughout Earth’s most extreme environments, such as the Kalahari Desert or the Arctic, hunter–gatherers found ingenious ways to obtain proteins and sugars provided by plants for dietary requirements. In the hyperarid Atacama Desert, wild plant resources are scarce and unevenly distributed due to limited water availability. This study brings together all available archaeobotanical evidence gathered in the Atacama Desert from the Late Pleistocene (ca. 13,000 cal bp) until the Inka epoch (ca. 450 cal bp) to help us comprehend when these populations acquired and managed useful plants from the coastal zone, Intermediate Depression, High Andes, as well as tropical and subtropical ecosystems. Widespread introduction of farming crops, water control techniques and cultivation of diverse plants by 3,000 cal bp ended not only a chronic food shortage, but also led to the establishment of a set of staple foods for the Atacama Desert dwellers, a legacy that remains visible today. By contrasting these trends with major sociocultural changes, together with palaeodemographic and climatic fluctuations, we note that humans adapted to, and transformed this hyperarid landscape and oscillating climate, with plants being a key factor in their success. This long-term process, which we term the “Green Revolution”, coincided with an exponential increase in the number of social groups inhabiting the Atacama Desert during the Late Holocene.

High temperatures are associated with substantial reductions in breeding success and offspring quality in an arid-zone bird.

During hot weather, terrestrial animals often seek shaded thermal refugia. However, this can result in missed foraging opportunities, loss of body condition and impaired parental care. We investigated whether such costs could compromise breeding success in a widespread southern African bird: the Southern Yellow-Billed Hornbill Tockus leucomelas. We predicted that hornbills might be especially vulnerable to temperature-dependant reductions in parents' foraging capacity due to extreme asymmetry in sex-specific roles during breeding: females are confined within the nest cavity for most of the nesting period and the burden of provisioning falls solely on the male during this time. We followed 50 hornbill nesting attempts in the Kalahari Desert between 2012 and 2015, collecting data on provisioning rates, adult and nestling body mass, fledging success and size of fledglings. Mean daily maximum air temperatures (Tmax) during nesting attempts ranged from 33.2 to 39.1°C. The likelihood of successful fledging fell below 50% at mean Tmax > 35.1°C; a threshold now regularly exceeded at our study site due to recent climate warming. Additionally, offspring fledging following the hottest nesting attempts were > 50% lighter than those fledging following the coolest. Sublethal costs of keeping cool including loss of body condition, production of poor-quality offspring and breeding failure are likely to become issues of serious conservation concern as climate change progresses; even for currently widespread species. Missed-opportunity costs associated with behavioral thermoregulation and direct sublethal costs of temperature exposure should not be overlooked as a potential threat to populations, especially in environments that are already hot.

Dust provenance and its role as a potential fertilizing agent for the Okavango Delta, Botswana

AbstractDust plays a globally important role in supplying biologically essential elements to landscapes underlain by nutrient‐poor substrates. Here we show that dust may play a significant role in sustaining productivity in the vast wetlands of the Okavango Delta in southern Africa, one of the world's richest biodiversity hotspots. Dust accumulates preferentially on tree‐covered islands in the seasonal swamps of the Delta, creating pockets of fine‐grained, nutrient‐rich material within the semi‐arid landscape of the Kalahari Desert. Strontium and neodymium isotopes reveal that this dust likely originates predominantly from the Makgadikgadi salt pans, located 300 km away, and contributes 10–80% of the fine‐grained material present in Okavango island soils. Surface material sourced from the Makgadikgadi Pans contains relatively high amounts of bioavailable phosphorus and iron, potentially influencing Okavango Delta biological productivity. We propose that long‐term ecosystem productivity and nutrient availability in the Okavango may be strongly mediated by regional dust inputs. Understanding the influence of dust deposition on nutrient loads and biogeochemical cycling is thus critical for predicting the response of the Okavango Delta to future changes in climate. We suggest that dust inputs may play a significant role in the supply of nutrients to other large, global wetland systems located in dryland environments. © 2020 John Wiley & Sons, Ltd

Ostrich eggshell bead strontium isotopes reveal persistent macroscale social networking across late Quaternary southern Africa

Hunter-gatherer exchange networks dampen subsistence and reproductive risks by building relationships of mutual support outside local groups that are underwritten by symbolic gift exchange. Hxaro, the system of delayed reciprocity between Ju/'hoãn individuals in southern Africa's Kalahari Desert, is the best-known such example and the basis for most analogies and models of hunter-gatherer exchange in prehistory. However, its antiquity, drivers, and development remain unclear, as they do for long-distance exchanges among African foragers more broadly. Here we show through strontium isotope analyses of ostrich eggshell beads from highland Lesotho, and associated strontium isoscape development, that such practices stretch back into the late Middle Stone Age. We argue that these exchange items originated beyond the macroband from groups occupying the more water-stressed subcontinental interior. Tracking the emergence and persistence of macroscale, transbiome social networks helps illuminate the evolution of social strategies needed to thrive in stochastic environments, strategies that in our case study show persistence over more than 33,000 y.

Winter thermoregulation in free-ranging pygmy falcons in the Kalahari Desert

Among birds, pronounced heterothermy tends to be used by small species belonging to phylogenetically older taxa and inhabiting environments with unpredictable and/or seasonally scarce food resources. Previous evidence suggests that a small arid-zone raptor, the pygmy falcon (Polihierax semitorquatus), enters torpor and decreases its body temperature (Tb) to below 31 °C on winter nights in the Kalahari Desert, where sub-zero night-time temperatures occur regularly. To confirm that this species has the capacity for heterothermy and to characterise its thermoregulatory patterns under natural conditions, we implanted temperature-sensitive radio transmitters into free-ranging falcons. Based on data from seven individuals, we found no evidence for the substantial reductions in Tb previously reported. The mean minimum rest-phase Tb during the study period was 37.89 ± 0.67 °C, we observed no instances of Tb < 36 °C, and air temperature did not significantly influence patterns of thermoregulation. Our results highlight intraspecific variability in heterothermy among birds and reveal that, contrary to previous suggestions, even in mid-winter pygmy falcons may not reduce Tb below normothermic levels.

Redescription of Paracrobeles laterellus Heyns, 1968 (Rhabditida: Cephalobidae) from Botswana

Summary Paracrobeles laterellus is redescribed from the North-West District (Koanaka Hill), Botswana, which forms part of the Kalahari Desert. A scanning electron microscopy study of the species is presented for the first time. This population is characterised by its adult body length, lateral field with three longitudinal incisures, lips with three tines, the middle one being shorter, primary and secondary axils with two guard processes, labial probolae bifurcate with basal ridge and smooth prongs, pharynx with very swollen and elongate metacorpus, spermatheca swollen, post-vulval uterine sac well developed, vagina sigmoid, female and male tails conoid, and characters of the spicules and gubernaculum. Morphologically, P. laterellus is very similar to P. kelsodunensis and P. mojavicus according to the morphology of the lip region, i.e., with two guard processes at the primary axils and robust spicules.

Heat dissipation behaviour of birds in seasonally hot arid‐zones: are there global patterns?

Quantifying organismal sensitivity to heat stress provides one means for predicting vulnerability to climate change. Birds are ideal for investigating this approach, as they display quantifiable fitness consequences associated with behavioural and physiological responses to heat stress. We used a recently developed method that examines correlations between readily‐observable behaviours and air temperature (Tair) to investigate interspecific variation in avian responses to heat stress in seasonally hot, arid regions on three continents: the southwestern United States, the Kalahari Desert of southern Africa and the Gascoyne region of western Australia. We found substantial interspecific variation in heat dissipation behaviours (wing‐drooping, panting, activity‐reduction, shade‐seeking) across all three regions. However, pooling the data revealed that little of this interspecific variation was systematically explained by organismal traits (foraging guild, diet, drinking dependency, body mass or activity levels) at the scale we tested. After accounting for phylogeny, we found that larger birds engaged in wing‐drooping behaviour at lower Tair and had lower activity levels at high Tair compared to smaller birds, indicating an effect of body mass on heat dissipation behaviour (HDB). In the Kalahari, reliance on drinking was correlated with significantly lower Tair at which panting commenced, suggesting a key role of water acquisition in HDB in that region. Birds also tended to retreat to shade at relatively lower Tair when more active, suggesting a behavioural trade‐off between activity, heat load and microsite selection. Our results imply that the causes underlying interspecific variation in heat dissipation behaviours are complex. While the variation we observed was not systematically explained by the broad scale organismal traits we considered, we predict that the indices themselves will still reflect vulnerability to potential fitness costs of high air temperatures. Further research is needed on a species‐specific basis to establish the functional significance of these indices.

Ecology rather than people restrict gene flow in Okavango‐Kalahari lions

AbstractReduced gene exchange between animal populations may be an indicator of the effects of anthropogenic fragmentation or it may reflect natural gradients in the landscape that can also result in population fragmentation. It can be difficult, therefore, to disentangle the role of local ecology from anthropogenic factors, creating a risk of attributing a lack of gene flow as being due to human activities, leading to ill‐informed management decisions. Here, we test the ecological and anthropogenic factors driving population differentiation and show how the relative influence of such effects can be identified. Using Bayesian clustering and a causal modelling approach, we combine genetic and remote sensing data to disentangle the confounding influences of ecological and anthropogenic fragmentation. We investigate a region where such confusion may arise; in and around the Okavango Delta in northern Botswana. Specifically, we used 20 microsatellites to investigate the genetic structuring of African lions Panthera leo occupying a landscape dominated by two very different environments, the wetland Okavango and the surrounding Kalahari Desert. We find that differences in ecology, rather than anthropogenic barriers, are driving genetic differences in the population and that despite their ability to disperse long distances these lion populations are differentiated into two distinct genetic groups, one inhabiting the wetland Okavango Delta and the other one inhabiting the surrounding dryland Kalahari, divided by an apparently unobstructed boundary. The genetic structure observed could easily have been misinterpreted as a response to anthropogenic disturbance reducing gene flow. This reinforces the need to consider non‐anthropogenic hypotheses, such as ecological differences between habitats, when assessing possible mechanisms of gene flow and their implications for population management. As anthropogenic pressure increases in this region, we recommend conservation managers consider the Okavango population as a separate conservation unit, but also recognize the importance of maintaining the current structural landscape connectivity.

The Mineral Composition and Sources of the Fine-Grained Sediments from the 49.6°E Hydrothermal Field at the SWIR

We used the X-ray diffraction method to determine systematically the mineral phases in bulk sediment samples and acid undissolved residuals of the fine-grained fraction of the surface sediments from the 49.6°E hydrothermal field at the Southwest Indian Ridge (SWIR) and discussed the mineral sources of the surface sediments. The results showed that the surface sediments in this region were composed of calcareous ooze, and calcite was the dominant mineral. The sediments also contained quartz, feldspar, clay minerals, pyroxene, sphalerite, barite, serpentine, and magnetite. The quartz, feldspar, and clay minerals were exogenous minerals that mainly originated from the Namib and Kalahari deserts in southern Africa. The pyroxene, serpentine, magnetite, sphalerite, calcite, and barite were endogenous minerals from weathering of seafloor basement rocks and seafloor hydrothermal activities. The sulfide particles in the sediments were mainly deposited from upwelling plumes.

Predictors of colony extinction vary by habitat type in social spiders.

Many animal societies are susceptible to mass mortality events and collapse. Elucidating how environmental pressures determine patterns of collapse is important for understanding how such societies function and evolve. Using the social spider Stegodyphus dumicola, we investigated the environmental drivers of colony extinction along two precipitation gradients across southern Africa, using the Namib and Kalahari deserts versus wetter savanna habitats to the north and east. We deployed experimental colonies (n = 242) along two ~ 800-km transects and returned to assess colony success in the field after 2 months. Specifically, we noted colony extinction events after the 2-month duration and collected environmental data on the correlates of those extinction events (e.g., evidence of ant attacks, no. of prey captured). We found that colony extinction events at desert sites were more frequently associated with attacks by predatory ants as compared with savanna sites, while colony extinctions in wetter savannas sites were more tightly associated with fungal outbreaks. Our findings support the hypothesis that environments vary in the selection pressures that they impose on social organisms, which may explain why different social phenotypes are often favored in each habitat.

South African Hydrostratigraphy: A conceptual framework

Abstract South African geology, geomorphology and climate are distinctly variable, resulting in a complex hydrological cycle superimposed on equally complex ground conditions. With fractured and karstic systems dominating the hydrogeology, thick vadose zones comprising soil and rock and at highly variable moisture conditions contribute to complex hydrostratigraphic systems comprising various confining and hydraulically connected units. This paper proposed standard terminology for basic concepts pertaining to the description of ground and water in the subsurface to eventually propose a hydrostratigraphic classification based on abiotic factors fairly constant over short periods of time (geology, geomorphology and climate), as well as those temporally highly variable (climate) and those introduced by human involvement (society). Ten major hydrostratigraphic units are eventually described, namely the Cape Fold Belt, Kalahari Desert, Witwatersrand Supergroup, Malmani Subgroup, Cenozoic Coastal Deposits, Saldanian Basement, Karoo Main Basin, Namaqua-Natal Metamorphics, Waterberg Group, and Archaean Granitoids.

The costs of keeping cool: behavioural trade-offs between foraging and thermoregulation are associated with significant mass losses in an arid-zone bird.

Avian responses to high environmental temperatures include retreating to cooler microsites and/or increasing rates of evaporative heat dissipation via panting, both of which may affect foraging success. We hypothesized that behavioural trade-offs constrain the maintenance of avian body condition in hot environments, and tested predictions arising from this hypothesis for male Southern Yellow-billed Hornbills (Tockus leucomelas) breeding in the Kalahari Desert. Operative temperatures experienced by the hornbills varied by up to 13°C among four microsite categories used by foraging males. Lower prey capture rates while panting and reductions associated with the occupancy of off-ground microsites, resulted in sharp declines in foraging efficiency during hot weather. Consequently, male body mass (Mb) gain between sunrise and sunset decreased with increasing daily maximum air temperature (Tmax), from ~ 5% when Tmax < 25°C to zero when Tmax = 38.4°C. Overnight Mb loss averaged ~ 4.5% irrespective of Tmax, creating a situation where nett 24-h Mb loss approached 5% on extremely hot days. These findings support the notion that temperature is a major determinant of body condition for arid-zone birds. Moreover, the strong temperature dependence of foraging success and body condition among male hornbills provisioning nests raises the possibility that male behavioural trade-offs translate into equally strong effects of hot weather on female condition and nest success. Our results also reveal how rapid anthropogenic climate change is likely to substantially decrease the probability of arid-zone birds like hornbills being able to successfully provision nests while maintaining their own condition.

Correction to: Science and education across cultures: another look at the Negev Bedouins and their environmental management practices

In p. 986, second paragraph should read, “For example, Chris Andersen (1997) described how Basarwa (Bushman) collected water while living in the Kalahari Desert

Chronic, sublethal effects of high temperatures will cause severe declines in southern African arid-zone birds during the 21st century

Birds inhabiting hot, arid regions are among the terrestrial organisms most vulnerable to climate change. The potential for increasingly frequent and intense heat waves to cause lethal dehydration and hyperthermia is well documented, but the consequences of sublethal fitness costs associated with chronic exposure to sustained hot weather remain unclear. Using data for species occurring in southern Africa's Kalahari Desert, we mapped exposure to acute lethal risks and chronic sublethal fitness costs under past, present, and future climates. For inactive birds in shaded microsites, the risks of lethal dehydration and hyperthermia will remain low during the 21st century. In contrast, exposure to conditions associated with chronic, sublethal costs related to progressive body mass loss, reduced nestling growth rates, or increased breeding failure will expand dramatically. For example, by the 2080s the region will experience 10-20 consecutive days per year on which Southern Pied Babblers (Turdoides bicolor) will lose ∼4% of body mass per day, conditions under which this species' persistence will be extremely unlikely. Similarly, exposure to air temperature maxima associated with delayed fledging, reduced fledgling size, and breeding failure will increase several-fold in Southern Yellow-billed Hornbills (Tockus leucomelas) and Southern Fiscals (Lanius collaris). Our analysis reveals that sublethal costs of chronic heat exposure are likely to drive large declines in avian diversity in the southern African arid zone by the end of the century.

Spatial and temporal variation in the use of supplementary food in an obligate termite specialist, the bat-eared fox

The bat-eared fox (Otocyon megalotis) is considered a termite specialist. However, studies of its diet have been limited to indirect methods, such as scat and stomach content analyses, resulting in intraspecific dietary variations due in part to methodological differences. Because diet plays a central role in the social dynamics of these canids, we hereby contribute further to our knowledge about their dietary habits. We present 2-year data of direct observations of foraging bouts of 19 habituated bat-eared foxes in the kalahari desert of South Africa, as well as data on seasonal variation in invertebrate prey communities obtained through pitfall and sweep net trapping. Despite showing a diet breadth reflective of a specialised forager across all seasons, foxes exhibited substantial seasonal variation in diet breadth with a broader range of food categories utilised in summer compared to the other seasons. Supplementary food categories appear to not have been utilised opportunistically, but it is unclear what drove the preference for some food categories over others. A literature review indicated strong effects of local conditions on the utilisation of supplementary food across southern Africa. Our data support bat-eared foxes as obligate termite specialists but highlight that they appear to have the ability to show dietary flexibility based on both temporal and spatial variations in food abundance.