Author
Mary Seely
Bio: Mary Seely is an academic researcher from University of the Witwatersrand. The author has contributed to research in topics: Desert climate & Sand dune stabilization. The author has an hindex of 24, co-authored 56 publications receiving 1688 citations.
Topics: Desert climate, Sand dune stabilization, Edaphic, Ecosystem, Soil water
Papers published on a yearly basis
Papers
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01 Jan 1995
145 citations
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TL;DR: Although null models for patterns in microbial communities were not supported by experimental data, the amount of unexplained variation suggests that stochastic processes also play a role in the assembly of such communities in the Namib Desert.
Abstract: The Namib Desert is considered the oldest desert in the world and hyperarid for the last 5 million years. However, the environmental buffering provided by quartz and other translucent rocks supports extensive hypolithic microbial communities. In this study, open soil and hypolithic microbial communities have been investigated along an East–West transect characterized by an inverse fog-rainfall gradient. Multivariate analysis showed that structurally different microbial communities occur in soil and in hypolithic zones. Using variation partitioning, we found that hypolithic communities exhibited a fog-related distribution as indicated by the significant East–West clustering. Sodium content was also an important environmental factor affecting the composition of both soil and hypolithic microbial communities. Finally, although null models for patterns in microbial communities were not supported by experimental data, the amount of unexplained variation (68–97 %) suggests that stochastic processes also play a role in the assembly of such communities in the Namib Desert.
105 citations
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TL;DR: In this paper, the authors highlight the pioneering work of Professor Gideon Louw's pioneering work on water relations and economy, which includes osmoregulation in desert plants and animals such as grass, beetles and springbok, established a foundation that inspired numerous studies by colleagues and students.
103 citations
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TL;DR: Three methods of fog-water uptake have been observed in three tribes of Namib desert dune tenebrionid beetles, Adesmiini, Eurychorini and Zophosini, showing specific behavioural patterns for drinking water condensed on vegetation, their own dorsum or sand.
Abstract: Three methods of fog-water uptake have been observed in three tribes of Namib desert dune tenebrionid beetles, Adesmiini, Eurychorini and Zophosini. The methods used correlate with distribution and gross morphology of each species but cut across phylogenetic affinities. Of the three methods described, none involve obvious fine anatomical or physical adaptations of the beetles for fog-water uptake. Rather, the beetles have evolved specific behavioural patterns for drinking water condensed on vegetation, their own dorsum or sand.Use of fog-water necessitates surface activity at times when surface temperatures and wind velocities are not optimal for these diurnal or crepuscular species. Behavioural adaptation has enabled these beetles to use irregular and unpredictable fogs as a moisture source.
91 citations
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TL;DR: This study uses multiple stable isotopes (2H, 18O, and 17O) to show that fog and dew have multiple origins and that groundwater in drylands can be recycled via evapotranspiration and redistributed to the upper soil profile as nonrainfall water.
Abstract: Dryland ecosystems cover 40% of the total land surface on Earth and are defined broadly as zones where precipitation is considerably less than the potential evapotranspiration. Nonrainfall waters (for example, fog and dew) are the least-studied and least-characterized components of the hydrological cycle, although they supply critical amounts of water for dryland ecosystems. The sources of nonrainfall waters are largely unknown for most systems. In addition, most field and modeling studies tend to consider all nonrainfall inputs as a single category because of technical constraints, which hinders prediction of dryland responses to future warming conditions. This study uses multiple stable isotopes ( 2 H, 18 O, and 17 O) to show that fog and dew have multiple origins and that groundwater in drylands can be recycled via evapotranspiration and redistributed to the upper soil profile as nonrainfall water. Surprisingly, the non–ocean-derived (locally generated) fog accounts for more than half of the total fog events, suggesting a potential shift from advection-dominated fog to radiation-dominated fog in the fog zone of the Namib Desert. This shift will have implications on the flora and fauna distribution in this fog-dependent system. We also demonstrate that fog and dew can be differentiated on the basis of the dominant fractionation (equilibrium and kinetic) processes during their formation using the 17 O- 18 O relationship. Our results are of great significance in an era of global climate change where the importance of nonrainfall water increases because rainfall is predicted to decline in many dryland ecosystems.
87 citations
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01 Jan 1987
TL;DR: Eisma et al. as mentioned in this paper showed that the CEC can vary over 2 orders of magnitude for various types of, minerals and can vary one order of magnitude within one soil type.
Abstract: Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):
1,169 citations
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TL;DR: The consequences of the presence and magnitude of different costs during different phases of the dispersal process, and their internal organisation through covariation with other life‐history traits are synthesised with respect to potential consequences for species conservation and the need for development of a new generation of spatial simulation models.
Abstract: Dispersal costs can be classified into energetic, time, risk and opportunity costs and may be levied directly or deferred during departure, transfer and settlement. They may equally be incurred during life stages before the actual dispersal event through investments in special morphologies. Because costs will eventually determine the performance of dispersing individuals and the evolution of dispersal, we here provide an extensive review on the different cost types that occur during dispersal in a wide array of organisms, ranging from micro-organisms to plants, invertebrates and vertebrates. In general, costs of transfer have been more widely documented in actively dispersing organisms, in contrast to a greater focus on costs during departure and settlement in plants and animals with a passive transfer phase. Costs related to the development of specific dispersal attributes appear to be much more prominent than previously accepted. Because costs induce trade-offs, they give rise to covariation between dispersal and other life-history traits at different scales of organismal organisation. The consequences of (i) the presence and magnitude of different costs during different phases of the dispersal process, and (ii) their internal organisation through covariation with other life-history traits, are synthesised with respect to potential consequences for species conservation and the need for development of a new generation of spatial simulation models.
1,049 citations
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TL;DR: It is proposed that such flow is often a key feature of the energetics, structure, and dynamics of populations, food webs, and communities whenever any two habitats, differing in productivity, are juxtaposed.
Abstract: This study quantifies the flow of energy and biomass from a productive marine system to a relatively unproductive terrestrial system. Biomass from marine food webs (here, the Gulf of California) enters the terrestrial webs of islands and coastal areas through two conduits: (1) shore drift of algal wrack and carrion and (2) colonies of seabirds. Both conduits support dense assemblages of consumers: arthropods are 85-560 times more abundant in the supralittoral than inland and 2.2 times more abundant on islands with seabird colonies than those without. Marine input (MI), not terrestrial primary productivity (TP) by land plants, provides most energy and biomass for terrestrial communities on 16 of 19 study islands. The ratio of perimeter to area (P/A) significantly predicts arthropod abundance on islands and is the major determinant of the relative importance of allochthonous flow; we expect P/A ratio to be important wherever transport of nutrients, detritus, and organisms among habitats occurs. Similar tran...
772 citations
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TL;DR: Female longevity was negatively correlated with number of progeny and positively correlated with age at first childbirth, and the findings show that human life histories involve a trade-off between longevity and reproduction.
Abstract: The disposable soma theory on the evolution of ageing states that longevity requires investments in somatic maintenance that reduce the resources available for reproduction. Experiments in Drosophila melanogaster indicate that trade-offs of this kind exist in non-human species. We have determined the interrelationship between longevity and reproductive success in Homo sapiens using a historical data set from the British aristocracy. The number of progeny was small when women died at an early age, increased with the age of death, reaching a plateau through the sixth, seventh and eighth decades of life, but decreased again in women who died at an age of 80 years or over. Age at first childbirth was lowest in women who died early and highest for women who died at the oldest ages. When account was taken only of women who had reached menopause, who were aged 60 years and over, female longevity was negatively correlated with number of progeny and positively correlated with age at first childbirth. The findings show that human life histories involve a trade-off between longevity and reproduction.
553 citations
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TL;DR: In this paper, a review of the state of the art in dryland fluvial research is presented, highlighting the need for a global review assessing the present state of knowledge.
467 citations