Long-term vegetation dynamics (40 yr) in the succulent Karoo, South Africa : effects of rainfall and grazing

QUESTIONS : Vegetation change in arid regions with a coefficient of rainfall exceeding 33% usually displays non-equilibrium dynamics, where abiotic factors override internal biotic controls. Irreversible changes have nonetheless also been described for arid regions. What are the contributions of internal/equilibriumvs external/non-equilibriumfactors to vegetation dynamics and can degradation due to overstocking be reversed after removal of livestock? LOCATION : Goegap Nature Reserve, Namaqualand, South Africa. METHODS : The descending point method was conducted annually from 1974 at two transects. Vegetation change was assessed in terms of vegetation cover, species composition, life-form composition, range condition, species richness and diversity. Principal coordinates analysis was used to illustrate the trajectories in floristic data, and the effects of stocking density and rainfall were examined with redundancy analysis. RESULTS : Vegetation cover, species richness and Shannon-Wiener index of diversity showed an increase and range condition improved with time. These positive changes could be related to the removal of high numbers of livestock and low wildlife numbers in the first years of survey. A gradual decline in the rate of increase in some of these parameters could be related to high grazing pressure during the later monitored years. There was a notable increase in nonsucculent chamaephytes, but the initial increase in succulent chamaephytes was not sustained. The directional change evident in perennial species composition, supports the equilibrium concept, whereby the negative changes induced by heavy grazing were partially reversed. Within the directional change, four quasi-stable states could be distinguished, which could be reconciled with the state-and-transition model. The annual component showed no directional change, but displayed event-driven, non-equilibrium dynamics by fluctuating in reaction to the timing and quantity of rainfall. CONCLUSIONS : The vegetation change displayed elements of both equilibrium and non-equilibrium dynamics, and demonstrated that the effects of heavy grazing in the Succulent Karoo were reversible. Overall, the recovery process proceeded slowly and was primarily detected in the perennial component of the vegetation. The increase in wildlife numbers in the later studied years and decline in perennial vegetation cover stress the need for active management of animal numbers to avoid vegetation degradation.University of Pretoria, the German Federal Ministry of Education and Research (BMBF) through the BIOTA South Project and the National Research Foundation (Grant no. 61277).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1654-109X2016-04-30hb201

n Fitososiologiese studie van die Hester Malan-natuurreservaat

The main aim of this study was to classify and describe plan.t communities in Hester Malan Nature Reserve using the Braun-Blanquet method. The vegetation of the Hester Malan Nature Reserve was also brought into context with the vegetation of the North-western Cape, and placed in an AcocKs Veld Type, the Namaqualand Broken Veld. The differences in the ephemeral vegetation between two years were determined, as well as the ratio between the ephemeral and the total vegetation of the Hester Malan Nature Reserve. The North-western Cape can be physiographically subdivided into a) a lowlying annual flat area, rainfall next to the coast and in the south, with an average between 0 and 150 mm, b) a mountainous central area with an average annual rainfall between 100 and 400 mm and c) a plateau in the east with an average annual rainfall of between 50 and 150 mm. The first two areas represent Namaqualand which is locally divided into the Richtersveld, the Sandveld, the Namaqualand Rocky Hills and the Knersvlakte. The plateau area is Known as Bushmanland. Western Mountain Karoo, Arid Karoo and Desert False Grassveld, Succulent Karoo, Orange River Broken Veld, Namaqualand Broken Veld, Strandveld of the West Coast, False Succulent Karoo, Mountain Renosterbosveld and Fynbos (AcocKs, 1975) is found in the North-1A1estern Cape. A phytosociological table, compiled from data obtained by means of a line transect survey, identified three communities in the Namaqualand Broken Veld, three communities in the Strandveld of the West Coast and one community in the Arid Karoo. Although the first two Veld Types receive predominantly winter rain and the latter predominantly summer rain, a floristic relationship between the two areas The Hester Malan Nature Reserve is situated in the Namaqualand Rocky Hills near Springbok and receives an average annual rainfall of 162 mm. The vegetation was classified using the Braun-Blanquet method. Floristic, structural, habitat and soil data was collected for 223 releuds and analysed into a phytosociological table, distinguishing four communities with two facies in the rocky hills and four communities with six facies in the flat areas with less or no rock. These communities were based on perennial species that were always present above ground. Ephemeral vegetation of two years were compared with each other with the aid of the Braun-Blanquet method and similarity indices. During the two years studied, the annual rainfall was 87,5 mm and 267,0 mm. Differences were found in comparable) ephemeral dominance differences vegetation 1 71 the dominance (constancy and cover) of the species (56% rather than in the species composition (75% comparable). The associations also differed in the two years. Differences in are therefore responsible for the well Known yearly physiognomic of the ephemeral vegetation in Namaqualand. The ephemeral consisted of about 10% of the total vegetation cover of the Hester Malan Nature Reserve. A list of 611 plant species occurring on the Hester Malan Nature Reserve was compiled 1,1Jith 14 species, 8 genera and 6 families in the Bryophyta; 5 species, 3 genera and 2 families in the Pteridophyta, and 592 species, 25 genera and 61 families in the Angiospermae.Dissertation (MSc)--University of Pretoria, 1988.Plant ScienceMScUnrestricte

Long-term vegetation change (>20 years) in the plains habitat on the Goegap Nature Reserve, Succulent Karoo, South Africa

Because vegetation change in arid ecosystems is slow, long-term data are essential to gain an understanding of how the vegetation responds to short-term, inter-annual variation in rainfall; long-term cyclic rainfall patterns; and grazing pressure. The point intercept method was conducted annually over a period of more than 20 years at five transects in the plains habitat on the Goegap Nature Reserve in the Northern Cape, South Africa. Vegetation change was assessed in terms of vegetation cover, species composition, species abundance, growth form composition, range condition and plant diversity. Non-metric multidimensional scaling was used to illustrate the trajectories in floristic data and to determine the strength of the correlations with rainfall and grazing variables. The effects of the high grazing pressure on the plains were apparent in the overall decrease in total plant cover and reductions in the cover of grazingsensitive species over the monitored period. Diversity parameters, of especially the annual component, were strongly related to rainfall. A directional change, which supports the equilibrium concept, was evident in changes in perennial species composition over time. The annual component, however, showed no directional change, but displayed eventdriven, non-equilibrium dynamics by fluctuating in reaction to the timing and quantity of rainfall.Keywords: diversity, equilibrium/non-equilibrium, rainfall, vegetation dynamics, wildlif

Complementarity of empirical and process-based approaches to modelling mosquito population dynamics with Aedes albopictus as an example: Application to the development of an operational mapping tool of vector populations

International audienceMosquitoes are responsible for the transmission of major pathogens worldwide. Modelling their population dynamics and mapping their distribution can contribute effectively to disease surveillance and control systems. Two main approaches are classically used to understand and predict mosquito abundance in space and time, namely empirical (or statistical) and process-based models. In this work, we used both approaches to model the population dynamics in Reunion Island of the 'Tiger mosquito', Aedes albopictus, a vector of dengue and chikungunya viruses, using rainfall and temperature data. We aimed to i) evaluate and compare the two types of models, and ii) develop an operational tool that could be used by public health authorities and vector control services. Our results showed that Ae. albopictus dynamics in Reunion Island are driven by both rainfall and temperature with a non-linear relationship. The predictions of the two approaches were consistent with the observed abundances of Ae. albopictus aquatic stages. An operational tool with a user-friendly interface was developed, allowing the creation of maps of Ae. albopictus densities over the whole territory using meteorological data collected from a network of weather stations. It is now routinely used by the services in charge of vector control in Reunion Island

Interaction between AIF and CHCHD4 Regulates Respiratory Chain Biogenesis

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein that, beyond its apoptotic function, is required for the normal expression of major respiratory chain complexes. Here we identified an AIF-interacting protein, CHCHD4, which is the central component of a redox-sensitive mitochondrial intermembrane space import machinery. Depletion or hypomorphic mutation of AIF caused a downregulation of CHCHD4 protein by diminishing its mitochondrial import. CHCHD4 depletion sufficed to induce a respiratory defect that mimicked that observed in AIF-deficient cells. CHCHD4 levels could be restored in AIF-deficient cells by enforcing its AIF-independent mitochondrial localization. This modified CHCHD4 protein reestablished respiratory function in AIF-deficient cells and enabled AIF-deficient embryoid bodies to undergo cavitation, a process of programmed cell death required for embryonic morphogenesis. These findings explain how AIF contributes to the biogenesis of respiratory chain complexes, and they establish an unexpected link between the vital function of AIF and the propensity of cells to undergo apoptosis