Foraging behaviour of scatter-hoarding gerbils (Gerbilliscus (Gerbillurus)) influences seed fate and dispersal for key plant species in the Namib Desert

Nonrainfall water inputs (e.g., fog and dew) are the least studied hydrological components in ecohydrology. The importance of nonrainfall waters on vegetation water status in arid ecosystems is receiving increasing attention. However, a clear understanding on how common plant water status benefits from nonrainfall waters, the impacts of different types of fog and dew events on vegetation water status, and the vegetation uptake mechanisms of nonrainfall waters is still lacking. In this study, we used concurrent leaf and soil water potential measurements from 3 years to investigate the species‐specific capacity to utilize moisture from fog and dew within the Namib Desert. Eight common plant species in the Namib Desert were selected. Our results showed that both fog and dew significantly increased soil water potential. Seven of the eight plant species studied responded to fog and dew events, although the magnitude of the response differed. Plants generally showed stronger responses to fog than to dew. Fog timing seemed to be an important factor determining vegetation response; for example, night fog did not affect plant water potential. We also found that Euclea pseudebenus and Faidherbia albida likely exploit fog moisture through foliar uptake. This study provides a first comprehensive assessment of the effects of nonrainfall waters on plant water status within the Namib Desert. Furthermore, this study highlights the importance of concurrent leaf and soil water potential measurements to identify the pathways of nonrainfall water use by desert vegetation. Our results fill a knowledge gap in dryland ecohydrology and have important implications for other drylands.

Summary 1 Although poorly studied and understood, the post‐dispersal movements and fates of seeds may affect critically the subsequent structure of plant communities, particularly in desert ecosystems where seeds can be the most abundant or only viable form of many plant species. We investigated the fate of experimental seeds of the desert mustard Lesquerella fendleri by examining seed dispersal and predation, and by quantifying the proportion of seeds that germinated and survived as seedlings in three different microsites within a New Mexico desert shrubland. 2 We found very limited seed dispersal but strong density‐dependent seed predation by rodents. There was a significant and consistent microsite effect in the proportion of soil seeds germinating and seedlings surviving to the end of the experiments. We did not find a consistent microsite effect for soil seed persistence, but did find a positive correlation between soil seed persistence and soil seed germination. Overall, these results indicate that seed predation may strongly affect the distribution of the seed bank, and that the abiotic environment may largely determine the extent to which soil seed populations in turn affect the distribution of emerging surface plants. 3 We present a seed fate model that synthesizes the results of the present and previous empirical investigations of the Lesquerella study system. This diagram illustrates how interactions among the abiotic environment, microsite variation and seed genotypes can determine which soil seeds successfully germinate and establish into the surface plant population. We suggest that the demography of desert surface plant populations may depend more on the time between seed inputs and the longevity of these seeds in the soil than on the amount of seeds produced at any one point in time and space.

The origin of sulphur in gypsum and dissolved sulphate in the Central Namib Desert, Namibia

Rhizosphere bacterial communities of Namib Desert plant species: Evidence of specialised plant-microbe associations.

Soil fungal diversity and assembly along a xeric stress gradient in the central Namib Desert

Fifty years of herpetological research in the Namib Desert and Namibia with an updated and annotated species checklist

310-PA12 The need for unique directly observed therapy (DOT) programs targeting TB patients (PTS) in inner cities in developed countries

Eolian, fluvial and pan (playa) facies of the Tertiary Tsondab Sandstone Formation in the central Namib Desert, Namibia

Ariadna spiders as bioindicator of heavy elements contamination in the Central Namib Desert

The formation of Namibia's extensive pedogenic gypsum crusts (CaSO4·2H2O) is interpreted in a new light. It is suggested that gypsum primarily precipitates at isolated points of evaporitic concentration, such as inland playas, and that deflation of evaporitic‐rich gypsum dust from these playas contributes to the formation of pedogenic gypsum duricrusts on the coastal gravel plains of the Namib Desert surrounding these playas. This study establishes the nature, extent and distribution of playas in the Central Namib Desert and provides evidence for playa gypsum deflation and gravel plain deposition. Remote sensing shows the distribution of playas, captures ongoing deflation and provides evidence of gypsum deflation. It is proposed that, following primary marine aerosol deposition, both inland playas and coastal sabkhas generate gypsum which through the process of playa deflation and gravel plain redeposition contributes to the extensive pedogenic crusts found in the Namib Desert region. Copyright © 2001 John Wiley & Sons, Ltd.

Thirty-six species of ant were collected in the central Namib Desert. South West Africa/Namibia during the period 1981 to 1985. The ant fauna was dominated by the Myrmicinae, comprising 29 species, followed by the Formicinae, comprising six species and the Pseudomyrmecinae with one species. The majority of ant species occurred on the gravel plains.

Generalizations about rare and endangered species are important for the development of conservation management policy and for understanding of the nature of rarity. Therefore, we sought such generalizations by statistically comparing eight life history and reproductive traits of rare and common plant species in two better-studied but climatically and geographically distinct Holarctic floras-those of California and the British Isles. Trends were often similar in both floras. Rare and common species differ significantly for a number of characters. In both floras, a woody habit was significantly more frequent for the rare species than the common species. Also, in both floras, monocarpy was less frequent in the rare species, significantly so in California. The rare species of both floras were, on average, significantly shorter in stature than the common species. This trend in stature remained significant when nonwoody species were compared but did not do so for woody species. Rare and common species differed with regard to their frequency of inflorescence structure types, but these differences were not concordant for both floras. The rare species of the British Isles had significantly higher proportions of mixed and polymorphic flower colors; the trend was not significant in California. In both floras, rare species had a higher frequency of many-seeded fruits, significantly so in California. California's rare species had a significantly higher frequency of dehiscent fruits than common species; the trend was reversed and not significant for the British Isles. We found no significant differences for characters associated with fruit dispersal. Finally, in California, the median altitude of the range of the common species was significantly greater than that of the rare species. At present, these correlates cannot be assigned as possible causes or consequences of rarity. Nonetheless, they may represent "high-risk" traits that could be used to identify other species already at risk or potentially at risk of becoming rarer.

The central Namib Desert is hyperarid, where limited plant growth ensures that biogeochemical processes are largely driven by microbial populations. Recent research has shown that niche partitioning is critically involved in the assembly of Namib Desert edaphic communities. However, these studies have mainly focussed on the Domain Bacteria. Using microbial community fingerprinting, we compared the assembly of the bacterial, fungal and archaeal populations of microbial communities across nine soil niches from four Namib Desert soil habitats (riverbed, dune, gravel plain and salt pan). Permutational multivariate analysis of variance indicated that the nine soil niches presented significantly different physicochemistries (R 2 = 0.8306, P ≤ 0.0001) and that bacterial, fungal and archaeal populations were soil niche specific (R 2 ≥ 0.64, P ≤ 0.001). However, the abiotic drivers of community structure were Domain-specific (P < 0.05), with P, clay and sand fraction, and NH4 influencing bacterial, fungal and archaeal communities, respectively. Soil physicochemistry and soil niche explained over 50% of the variation in community structure, and communities displayed strong non-random patterns of co-occurrence. Taken together, these results demonstrate that in central Namib Desert soil microbial communities, assembly is principally driven by deterministic processes.

Knowledge of long-term rainfall variablity is essential for water management in Namibia. Data relevant to assess this variability are scarce because of the lack of long instrumental climate records and the limited potential of standard highresolution proxy records. In northern and eastern Africa the reconstruction of Holocene tropical lake-level changes has established alternating phases of desiccation and of high stands with lake-levels more than 100 m above the present level. This record of paleohydrological changes is impressive as compared to available data collected from modern instrumented observations. Such sudden and dramatic changes of the hydrologic regime within time scales that are relevant to human societies are not known from southwestern arid Africa (Namib Desert). Fluvial silts, accumulated in some Namib valleys, are interpreted as records of reduced precipitation in the catchments. Our investigations show that these fluvial silts are slack water deposits (SWDs) and reflect hydrologic - and climatic - conditions during the late Holocene that caused extreme flash floods in the valleys. Here we describe SWDs of some Namibian Desert valleys and present 14C dates of their ages. The youngest accumulation phase occurred during the Little Ice Age (LIA)(ca. AD 1300 to 1850). The biggest flash floods of the LIA, in most catchments, experienced water levels in the valleys that exceeded the most extreme floods of the last 100 - 150 years. In the northwestern Namib Desert, flash floods of the LIA were more frequent and more extreme than in the central Namib Desert. This may be caused by small shifts of the tropical-temperate-troughs in southern Africa and the south west Indian Ocean.

Chapter 6 - Microbial ecology of the Namib Desert