Desert ungulates live in adverse ecosystems that are particularly sensitive to degradation and global climate change. Here, we asked how two ungulate species with contrasting feeding habits, grazing ...gemsbok (Oryx g. gazella) and browsing springbok (Antidorcas marsupialis), respond to an increase in food availability during a pronounced rain period. We used a stable isotope approach to delineate the feeding habits of these two ungulates in the arid Kunene Region of Namibia. Our nineteen months field investigation included two time periods of drought when food availability for ungulates was lowest and an intermediate period with extreme, unusual rainfalls. We documented thirteen isotopically distinct food sources in the isotopic space of the study area. Our results indicated a relatively high dietary plasticity of gemsbok, which fed on a mixture of plants, including more than 30% of C3 plants during drought periods, but almost exclusively on C4 and CAM plant types when food was plentiful. During drought periods, the inferred gemsbok diets also consisted of up to 25% of Euphorbia damarana; an endemic CAM plant that is rich in toxic secondary plant compounds. In contrast, springbok were generalists, feeding on a higher proportion of C3 than C4/CAM plants, irrespective of environmental conditions. Our results illustrate two dietary strategies in gemsbok and springbok which enable them to survive and coexist in the hostile Kunene arid ecosystem.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Characteristic vegetation and biofuels in major ecosystems of southern Africa were sampled during summer and autumn 2000 and burned under semicontrolled conditions. Elemental compositions of fuels ...and ash and emissions of CO2, CO, CH3COOH, HCOOH, NOX, NH3, HONO, HNO3, HCl, total volatile inorganic Cl and Br, SO2 and particulate C, N, and major ions were measured. Modified combustion efficiencies (MCEs, median = 0.94) were similar to those of ambient fires. Elemental emissions factors (EFel) for CH3COOH were inversely correlated with MCEs; EFels for heading and mixed grass fires were higher than those for backing fires of comparable MCEs. NOX, NH3, HONO, and particulate N accounted for a median of 22% of emitted N; HNO3 emissions were insignificant. Grass fires with the highest EFels for NH3 corresponded to MCEs in the range of 0.93; grass fires with higher and low MCEs exhibited lower EFels. NH3 emissions for most fuels were poorly correlated with fuel N. Most Cl and Br in fuel was emitted during combustion (median for each = 73%). Inorganic gases and particulate ions accounted for medians of 53% and 30% of emitted Cl and Br, respectively. About half of volatile inorganic Cl was HCl indicating significant emissions of other gaseous inorganic Cl species. Most fuel S (median = 76%) was emitted during combustion; SO2 and particulate SO42− accounted for about half the flux. Mobilization of P by fire (median emission = 82%) implies large nutrient losses from burned regions and potentially important exogenous sources of fertilization for downwind ecosystems.
Desert ungulates live in adverse ecosystems that are particularly sensitive to degradation and global climate change. Here, we asked how two ungulate species with contrasting feeding habits, grazing ...gemsbok (Oryx g. gazella) and browsing springbok (Antidorcas marsupialis), respond to an increase in food availability during a pronounced rain period. We used a stable isotope approach to delineate the feeding habits of these two ungulates in the arid Kunene Region of Namibia. Our nineteen months field investigation included two time periods of drought when food availability for ungulates was lowest and an intermediate period with extreme, unusual rainfalls. We documented thirteen isotopically distinct food sources in the isotopic space of the study area. Our results indicated a relatively high dietary plasticity of gemsbok, which fed on a mixture of plants, including more than 30% of C3 plants during drought periods, but almost exclusively on C4 and CAM plant types when food was plentiful. During drought periods, the inferred gemsbok diets also consisted of up to 25% of Euphorbia damarana; an endemic CAM plant that is rich in toxic secondary plant compounds. In contrast, springbok were generalists, feeding on a higher proportion of C3 than C4/CAM plants, irrespective of environmental conditions. Our results illustrate two dietary strategies in gemsbok and springbok which enable them to survive and coexist in the hostile Kunene arid ecosystem.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A dissertation submitted to the Faculty of Science, University;
of the Witwatersrand, Johannesburg, in fulfilment of the;
requirements for the degree of Doctor of Philosophy;
Okaukuejo 1993
This ...study was designed to investigate the eco-physiology of;
baboons (Papio cynocephalus ursinus) in a troop living in the;
Kuiseb River canyon of;
the central Namib desert, Namibia.;
Answers were sought for two major questions: what Were the;
baboons prospects for survival and were there special adaptations;
allowing for their survival in their desert environment? To;
answer the former, life history phenomena of individuals and;
demographic changes within the troop were studied over a six year;
period. Results showed that the troop was not self-sustaining.;
Ectco-parasite infestations killed the majority of infants born to;
high ranking female baboons, while infant kidnapping by high;
ranking females killed most lower ranking females' infants. The;
high infant mortality appeared to affect the behaviour of adult;
male baboons in the troop, causing non-paternal males to fight;
harder to maintain a rank with reproductive opportunities,;
usually with serious wounding or death as a consequence. Answers;
to the latter question involved investigation into the baboons;
feeding patterns and diet, body temperature regulation, water;
flux rates and methods of body water conservation. Despite their;
desert environment, the baboons had access to plants of high;
water content and Were not dependent on free water intake. Plant;
foods also had low electrolyte concentrations. Body temparetures;
of three free-ranging baboons recorded by intraperitoneal radio;
tolemeters were remarkably labile, indicating an adaptive;
heterothermy. The baboons appeared to employ evaporative cooling;
only when water was available to drink and used cool sub-surface;
sand to slow their body temperature rises. water flux rates;
determined using tritiated water of three free-ranging baboons;
were not different to those of baboons from elsewhere.;
Acquisition of free water at times of water scarcity was strictly;
rank related. Body water conservation was apparently achieved;
through a combination of factors: urine concentration of Kuiseb;
baboons increased significantly when they were water deprived.;
The kidneys of the Kuiseb baboons, obtained from baboons that;
died naturally were anatomically significantly different and;
head greater urine concentrating abilities than the kidneys Of;
baboons from the northern Transvaal, South Africa. Kuiseb;
baboons showed efficient faecal water conservation, similar to;
other desert adapted mammals, Body water also was apparently;
conserved by engaging in water conservative behaviour,;
predominantly inactivity.
Abstract
Elephant low-frequency calls and atmospheric conditions that influence the transmission and detection of these calls were recorded at a fixed location over a period of about 3 weeks at the ...end of the dry season in the Etosha National Park, Namibia. A bimodal distribution in elephant call detections is observed, with the primary maximum (42% of all calls) occurring in a 3-h period following sunset and a secondary maximum (29% of all calls) in a 2-h period following sunrise.
This distribution in calls detected is shown to depend upon marked and regular changes over 24 h in near-surface atmospheric stability and velocity, which determine propagation ranges. The observed bimodal distribution of calls detected depends upon these changes in atmospheric conditions as well as the location of the caller and the rate of calling. The findings are supported by results from an atmospheric acoustic model but are at variance with observations of the number of calls made from collared elephants in markedly different habitat.
Detection of calls heard at a location remote from the caller represents a valuable and noninvasive research and applied tool that, however, must take note of atmospheric conditions that govern the propagation and reception of such signals.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Plants must regulate their use of absorbed light energy on a minute-by-minute basis to maximize the efficiency of photosynthesis and to protect photosystem II (PSII) reaction centers from ...photooxidative damage. The regulation of light harvesting involves the photoprotective dissipation of excess absorbed light energy in the light-harvesting antenna complexes (LHCs) as heat. Here, we report an investigation into the structural basis of light-harvesting regulation in intact spinach (Spinacia olerácea) chloroplasts using freeze-fracture electron microscopy, combined with laser confocal microscopy employing the fluorescence recovery after photobleaching technique. The results demonstrate that formation of the photoprotective state requires a structural reorganization of the photosynthetic membrane involving dissociation of LHCII from PSII and its aggregation. The structural changes are manifested by a reduced mobility of LHC antenna chlorophyll proteins. It is demonstrated that these changes occur rapidly and reversibly within 5 min of illumination and dark relaxation, are dependent on ∆pH, and are enhanced by the deepoxidation of violaxanthin to zeaxanthin.
Summary
We characterized a set of Arabidopsis mutants deficient in specific light‐harvesting proteins, using freeze‐fracture electron microscopy to probe the organization of complexes in the membrane ...and confocal fluorescence recovery after photobleaching to probe the dynamics of thylakoid membranes within intact chloroplasts. The same methods were used to characterize mutants lacking or over‐expressing PsbS, a protein related to light‐harvesting complexes that appears to play a role in regulation of photosynthetic light harvesting. We found that changes in the complement of light‐harvesting complexes and PsbS have striking effects on the photosystem II macrostructure, and that these effects correlate with changes in the mobility of chlorophyll proteins within the thylakoid membrane. The mobility of chlorophyll proteins was found to correlate with the extent of photoprotective non‐photochemical quenching, consistent with the idea that non‐photochemical quenching involves extensive re‐organization of complexes in the membrane. We suggest that a key feature of the physiological function of PsbS is to decrease the formation of ordered semi‐crystalline arrays of photosystem II in the low‐light state. Thus the presence of PsbS leads to an increase in the fluidity of the membrane, accelerating the re‐organization of the photosystem II macrostructure that is necessary for induction of non‐photochemical quenching.
Summary
The diffusion of proteins in chloroplast thylakoid membranes is believed to be important for processes including the photosystem‐II repair cycle and the regulation of light harvesting. ...However, to date there is very little direct information on the mobility of thylakoid proteins. We have used fluorescence recovery after photobleaching in a laser‐scanning confocal microscope to visualize in real time the exchange of chlorophyll proteins between grana in intact spinach (Spinacia oleracea L.) and Arabidopsis chloroplasts. Most chlorophyll proteins in the grana appear immobile on the 10‐min timescale of our measurements. However, a limited population of chlorophyll proteins (accounting for around 15% of chlorophyll fluorescence) can exchange between grana on this timescale. In intact, wild‐type chloroplasts this mobile population increases significantly after photoinhibition, consistent with a role for protein diffusion in the photosystem‐II repair cycle. No such increase in mobility is seen in isolated grana membranes, or in the Arabidopsis stn8 and stn7 stn8 mutants, which lack the protein kinases required for phosphorylation of photosystem II core proteins and light‐harvesting complexes. Furthermore, mobility under low‐light conditions is significantly lower in stn8 and stn7 stn8 plants than in wild‐type Arabidopsis. The changes in protein mobility correlate with changes in the packing density and size of thylakoid protein complexes, as observed by freeze‐fracture electron microscopy. We conclude that protein phosphorylation switches the membrane system to a more fluid state, thus facilitating the photosystem‐II repair cycle.
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