scholarly journals Survival strategies of sharptooth catfish Clarias gariepinus in desiccating pans in the northern Kruger National Park

Koedoe ◽  
1998 ◽  
Vol 41 (2) ◽  
Author(s):  
B.C.W. Van der Waal
Keyword(s):  
National Park ◽  
Clarias Gariepinus ◽  
High Water ◽  
Survival Strategies ◽  
Small Fish ◽  
Large Bulk ◽  
Drying Up ◽  
Fish Remains ◽  
Adverse Environmental Conditions ◽  
Dry Out

Observations in drying out pans showed that small (26-37 cm) sharptooth catfish (Clarias gariepinus) can hide at the bottom of small pools filled with sticky mud whereas larger fish stay afloat at the surface in larger pools with sloppy mud, where they easily become prey or succumb to heat stress. The inability of larger fish to keep down in the sloppy mud of up to 40 cm depth is the result of their large bulk and high density of the mud. This may indicate a survival advantage for smaller fish in the final dry-out phase of pools and is supported by the presence of only small fish remains in the last drying up pools of dry pans. Another adaptation of smaller fish includes the temporary congregation outside the water enabling concealment under dense vegetation as a means to escape adverse environmental conditions, including high water temperatures and avian predation. The advantage small fish have over larger catfish under these extreme conditions may explain why catfish are known to show a wide variation in growth rate under natural and aquaculture conditions.

scholarly journals Structure, Diversity, and Environmental Determinants of High-Latitude Threatened Conifer Forests

Forests ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 775
Author(s):  
Carlos Esse ◽  
Francisco Correa-Araneda ◽  
Cristian Acuña ◽  
Rodrigo Santander-Massa ◽  
Patricio De Los Ríos-Escalante ◽  
...  
Keyword(s):  
Water Table ◽  
Environmental Variables ◽  
National Park ◽  
High Water ◽  
Forest Communities ◽  
Competitive Effect ◽  
Forest Patches ◽  
Last Glaciation ◽  
The World ◽  
Local Topography

Pilgerodendron uviferum (D. Don) Florin is an endemic, threatened conifer that grows in South America. In the sub-Antarctic territory, one of the most isolated places in the world, some forest patches remain untouched since the last glaciation. In this study, we analyze the tree structure and tree diversity and characterize the environmental conditions where P. uviferum-dominated stands develop within the Magellanic islands in Kawésqar National Park, Chile. An environmental matrix using the databases WorldClim and SoilGrids and local topography variables was used to identify the main environmental variables that explain the P. uviferum-dominated stands. PCA was used to reduce the environmental variables, and PERMANOVA and nMDS were used to evaluate differences among forest communities. The results show that two forest communities are present within the Magellanic islands. Both forest communities share the fact that they can persist over time due to the high water table that limits the competitive effect from other tree species less tolerant to high soil water table and organic matter. Our results contribute to knowledge of the species’ environmental preference and design conservation programs.

scholarly journals Freshwater fishes of Bontebok National Park

Koedoe ◽  
2001 ◽  
Vol 44 (2) ◽  
Author(s):  
I.A. Russell
Keyword(s):  
South African ◽  
National Park ◽  
Fish Assemblages ◽  
Micropterus Salmoides ◽  
Clarias Gariepinus ◽  
Lepomis Macrochirus ◽  
River System ◽  
Indigenous Species ◽  
Freshwater Species ◽  
Micropterus Dolomieu

Fish assemblages were sampled at six sites in the Breede River in the Bontebok National Park during 1999 and 2000. A total of 380 fish from 12 species was recorded. Indigenous fish collected included one freshwater species (Barbus andrewi), two catodromous species (Anguilla mossambica, Myxus capensis). and three estuarine species (Gilchris- tella aestuaria, Monodactylusfalciformis, Mugil cephalus). Four of the species recorded were aliens (Tinea tinea, Lepomis macrochirus, Micropterus salmoides, Micropterus dolomieu) and two species translocated from other South African rivers (Tilapia sparrmanii, Clarias gariepinus). A further two indigenous species (Sandelia capensis, Pseudobarbus biirchelli) could potentially occur within the park, though the high abundance of alien predators means that there is little chance for recolonisation from tributaries higher in the Breede River system. There is little opportunity to meaningfully conserve most indigenous freshwater fish in Bontebok National Park.

scholarly journals Fish and other faunal remains from a Late Iron Age site on the Letaba River, Kruger National Park

Koedoe ◽  
1991 ◽  
Vol 34 (1) ◽  
Author(s):  
Ina Plug ◽  
Paul Skelton
Keyword(s):  
Iron Age ◽  
National Park ◽  
Fish Population ◽  
Faunal Remains ◽  
Late Iron Age ◽  
Hunting Strategies ◽  
The People ◽  
Large Numbers ◽  
Fish Remains ◽  
Insight Into

Fish remains from Late Iron Age sites in the Transvaal are relatively scarce. It seems as if the people did not utilize the riverine resources extensively. Therefore the unique assemblage of large numbers of fish bones on a Late Iron Age site, provides some insight into the fish population of a section of the Letaba River a few hundred years ago. The presence of other faunal remains provides some information on prehistoric utilization of the environment in general. Hunting strategies and aspects of herding can also be deduced from the faunal remains.

Sediments of the Tay Estuary. II. Formation of Ephemeral Zones of High Suspended Sediment Concentrations.

1975 ◽  
Vol 75 (1-2) ◽  
pp. 65-89 ◽  
Author(s):  
A. T. Buller
Keyword(s):  
Suspended Sediment ◽  
River Discharge ◽  
High Tide ◽  
High Water ◽  
Main Channel ◽  
Tidal State ◽  
Suspended Sediment Concentrations ◽  
High Concentrations ◽  
Calm Weather ◽  
Dry Out

SynopsisDuring periods of sustained moderate river discharge and quiescent marine conditions little external suspended sediment enters the estuarine circulation of the Tay. That material which is in suspension is largely derived from the estuary margins where tidal currents superimposed by wind-induced waves are competent to resuspend fine material from the surface of the ‘mud’ flats and erode bedded silts from the incised banks of minor channels and runnels draining them. The quantities of this sediment entering the system are largely determined by tidal state and amplitude, as well as wind velocity.On spring tides the flats are entirely covered at high water, and dry out completely at low water. The volume of water and its areal coverage at high tide ensures that, during the ebb, water charged with high concentrations of suspended sediment is directed from the fiats into the surface and middepth waters of the main channel. This process acting along the 20 km length of the channel flanking the ‘mud’ flats, combined with the low tide ‘ponding effect’ caused by the tide flooding from the sea while the upper estuarine water is still ebbing, results in the cumulative formation of a zone of high suspended sediment concentrations (turbidity maximum). As the flood tide becomes fully established the zone is diluted and dispersed. During neap tides the same processes operate, but because a smaller area of the flats is covered at high water and uncovered at low water, and because neap tidal current speeds are lower than those for spring tides, two proportionally weaker zones are recognised.Following periods of sustained moderate river discharge, quiet sea conditions and calm weather, suspended sediment concentrations in the Tay are negligible irrespective of tidal state or amplitude.

Approaches to elucidate the basis of desiccation-tolerance in seeds

1997 ◽  
Vol 7 (2) ◽  
pp. 75-95 ◽  
Author(s):  
Allison R. Kermode
Keyword(s):  
Water Deficit ◽  
Desiccation Tolerance ◽  
Protein Function ◽  
High Water ◽  
Late Embryogenesis Abundant ◽  
Plant Responses ◽  
Late Embryogenesis ◽  
Essential Components ◽  
Orthodox Seeds ◽  
Adverse Environmental Conditions

AbstractPlants undergo a series of physiological, biochemical and molecular changes in response to adverse environmental conditions or stresses such as drought, low temperature or high salt. Several genes and their corresponding proteins have been described that may play a role in withstanding water-deficit-related stresses or full desiccation. In particular, sugars and late-embryogenesis-abundant (LEA) proteins have received the most attention. Plant responses to water-deficit and desiccation have been well-characterized at the molecular level; however, pinpointing the precise roles of the gene products in protecting cells under conditions of water deficit remains a challenging task. While few plants are capable of withstanding full desiccation, most seeds undergo this event as a pre-programmed and final stage in their development. These are the so-called ‘orthodox’ seeds. In contrast to seeds of orthodox species, those of recalcitrant species do not acquire desiccation tolerance during their development and are shed from the parent plant at relatively high water contents. The essential components of desiccation tolerance of seeds are likely to involve the ability to effect repair upon subsequent rehydration as well as the ability to accumulate protective substances that limit the amount of damage which otherwise would be caused by water loss. Studies have begun to examine whether the desiccation sensitivity of recalcitrant seeds is at least partially the result of an insufficient accumulation of LEA-type proteins, or whether other factors (including a lack of protective sugars) are more important. This review assesses some of these studies as well as recent research to understand gene and protein function using transgenic host plant systems.

Comment upon the Economic Potential of Fish Utilization in Riverine Environments and Potential Archaeological Biases

1980 ◽  
Vol 45 (3) ◽  
pp. 562-567 ◽  
Author(s):  
Adam G. Garson
Keyword(s):  
Small Fish ◽  
South American ◽  
Economic Potential ◽  
Fish Size ◽  
Recovery Techniques ◽  
Seasonal And Spatial Variations ◽  
Fish Exploitation ◽  
Fish Remains ◽  
Fish Productivity ◽  
High Fish

New data from the South American lowland tropics are used in support of a recent argument extolling the potential of fish utilization in major floodplains. The discussion will cover five points: (1) major floodplains in general, and the Amazon and Orinoco floodplains in particular, have similar characteristics that make them biologically productive regions; (2) high fish productivity and the use of mass-fishing techniques in floodplain regions are characteristics of lowland South America; (3) the ecological dynamics of the seasonally inundated savanna are particularly productive and propitious for seasonal exploitation using mass-fishing techniques; (4) differences in species composition and fish size may have implications for seasonal and spatial variations in fish exploitation; and (5) substantial biases are apparent against the retrieval of small fish remains using traditional archaeological recovery techniques.

scholarly journals SPATIAL STRUCTURE OF VEGETATION OF LARGE LAKES OF THE ONEGA PENINSULA (ON THE EXAMPLE OF MURAKANSKOE AND BOLSHOE VYGOZERO LAKE)

2021 ◽  
pp. 41-51
Author(s):  
D. Moseev ◽  
A. Krasheninnikov ◽  
A. Bragin ◽  
A. Lohov
Keyword(s):  
Spatial Structure ◽  
National Parks ◽  
National Park ◽  
Aquatic Vegetation ◽  
High Water ◽  
Water Transparency ◽  
Comparative Characteristic ◽  
Large Lakes ◽  
Ph Values ◽  
The North

Studying the vegetation of freshwater lakes remains a topical subject in the national parks of the Arkhangelsk Region. It is in particular important for the Onega Pomorie National Park, which is located along the coasts of the Onega and Dvinskoy bays (of the White Sea) in the northern part of the Onega Peninsula. This article examines the spatial structure of aquatic and coastal-aquatic vegetation of Murakanskoye and Bolshoye Vygozero – two large lakes of the Onega Peninsula. The spatial structure is presented in the form of ecological series of associations of plant communities. A comparative characteristic of the lakes’ vegetation is given in the discussion of the article. The littoral zone is poorly developed in both lakes mentioned above. It depends on the openness of the water areas to the winds from the north. It is indicated that the species composition and vegetation structure of the Bolshoye Vygozero Lake mostly depends on water transparency and high acidity; these factors determine the development of the Phragmitetum australis fontinaliosum dalecarlicae, Phragmitetum australis caricosum aquatilis, Caricetum aquatilis associations. In the Murakanskoe Lake, high water transparency and slightly alkaline pH values contribute to the development of communities of pondweeds – such as Potamogeton alpinus, Potamogeton praelongus, and communities of the Lobelietum dortmannae isoëtosum echinosporae association.

scholarly journals Vegetation near Santa Teresinha, NE Mato Grosso.

1985 ◽  
Vol 15 (3-4) ◽  
pp. 275-302 ◽  
Author(s):  
George Eiten
Keyword(s):  
Plant Growth ◽  
Woody Plant ◽  
Ground Cover ◽  
High Water ◽  
Dry Season ◽  
Mato Grosso ◽  
Gallery Forests ◽  
Seasonally Flooded ◽  
Dry Out ◽  
Regional Water

The Santa Tenesinha region in northeaster Mato Grosso has a varied vegetation which is principally hammock pantanal. The flat clayey alluvial ground between the hummocks is coveted with a continuous non-cerrado ground cover dominated by grasses but which harbors sedges and a lange herb flora. No woody plants grow in it. The tops of the 10-20m wide, slightly elliptical hummocks, 1.5-2 m high, 10-40 per hectare, are covered with cerrado plants: herbs, semlshrubs, thin- and thick-stemmed shrubs and low trees. For 4-5 months during the latter part of the rainy season, the regional water table rises to the surface and the ground between the hummocks becomes saturated or floods up to 1.5-2 m deep. The tops of the hummocks almost always remain above high water level. In the dry season the surface soil dries out completely. This alternation of saturation or shallow flooding and dryness, prevents woody plant, growth between the hummocks, and except for a few tolerant species, also prevents woody plant. growth on the lower part of the hummochs. The gallery forests in the pantanal are seasonally flooded more deeply but their soil does not dry out so thonoughly in the dry season so woody plant growth is not prevented.

scholarly journals The Influence of Lubrication on Electrical and Mechanical Parameters of Potentiometer Resistive Element

1985 ◽  
Vol 12 (1) ◽  
pp. 33-40
Author(s):  
S. Nowak ◽  
B. Herod
Keyword(s):  
Thin Film ◽  
Protective Coating ◽  
Environmental Influences ◽  
High Water ◽  
Production Costs ◽  
Major Influence ◽  
Water Desorption ◽  
Resistive Element ◽  
Effective Seal ◽  
Dry Out

Fixed resistors are usually protected against environmental influences. For this aim, special lacquers are used. Much of the environmental qualities of such a resistor are directly related to its enclosure.The resistive element of the potentiometer cannot be protected in the same way. The producers of quality potentiometers, especially thin film ones, designed an effective seal of their housing but it leads to an increase in production costs.The first researches on thin film resistive elements for potentiometers, proved the major sensitivity of the unit to moisture cycling, because of high water chemisorption on the resistive element surface.The chemisorption effect has the major influence on the temperature coefficient of resistance (TCR), because at a higher temperature, water desorption is occuring and the resistance of the film is undergoing a change.However, the IEC Standard recommends dry out of resistive elements before TCR measurement; the potentiometer users feel that total resistance changes as a sum of temperature change and drying out change.The present paper deals with trials to eliminate this disadvantage of thin film potentiometers by protection against moisture.The protective coating should, because of its affinity to the resistive film, form durable protection against environmental influences, but should not increase the contact resistance of the wiper (CRV). Such a coating also should not increase the friction coefficient of the wiper.To verify the hypothesis that polar lubricants can play a part in protective coating of thin film potentiometers, several different lubricants have been examined.

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