1. Study of the structure and mode of life of Malleus regula provides the basis for consideration of the "hammer" species, M. malleus and M. albus.
2. M. regula occurs byssally attached, vertically disposed on rocky substrates associated with mud and is widely distributed in the tropical Indo-Pacific.
3. The distal two-thirds of the elongated shell is exclusively prismatic. By means of special pallial retractors the mantle lobes can be withdrawn within the nacreous region.
4. The massive opisthodetic ligament has a short secondary extension of fusion layer.
5. A promyal chamber on the right side proximal to the adductor increases water flow into the exhalant chamber.
6. The long filibranch ctenidia provide a vertically extended food-collecting surface.
7. The foot is concerned with planting of the massive byssus which emerges through a notch in the right valve but on the under ( i.e., dorsal) surface. There is also a unique and very long accessory foot, ventrally grooved, everywhere ciliated and in constant writhing activity due to blood pressure and intrinsic muscle. Moving freely throughout the lower mantle cavity it can only be concerned with cleansing.
8. Pseudofaeces are ejected from the distal tip of the mantle cavity.
9. M. malleus, the black hammer shell, occurs vertically embedded in coarse sand or sandy gravel. Byssus threads are attached to fragments within the substrate. The great anterior and posterior elongations of the hinge line (also exclusively prismatic) are separated by the byssal notch (now affecting both valves).
10. Shells are usually excessively irregular due to the great exposure to damage and the almost unlimited powers of rapid repair by the three pallial extensions.
11. M. albus, the white hammer shell, is stouter and inhabits muddy sand. During growth it loses the byssus with reduction of the foot and byssal retractors and closure of the byssal notch. The accessory foot is not affected. The animal becomes anchored in the substrate exclusively by the anterior and posterior extensions of the shell.
12. Description of the typically rounded Isognomon ephippium leads to that of the elongated I. isognomon which occupies precisely the same habitat as M. regula.
13. It lacks the pallial retractors, promyal chamber and accessory foot of Malleus, the nacreous region is more extended distally and the ligament is multivincular (the formation of which is discussed), producing some posterior, but never any anterior, extension of the hinge line.
14. A remarkably dense mixed bed of M. regula and I. isognomon in Darvel Bay, Sabah (Borneo), is described. Different spawning periods, by preventing competition during settlement, may account for this complete intermixing of sympatric species, which, however, are generalized herbivores where numbers are not limited by food supply.
15. From a basic epifaunal habit (Pteria, Isognomon, M. regula), members of the Pteriacea have become adapted for infaunal life within sponges (Vulsella, Crenatula) or within soft substrates ( M. malleus, M. alba and the Pinnidae).
16. There is final discussion about elongation in monomyarians, i.e., in the genus Malleus and in I. isognomon.
Between April 1987 and March 1988, populations of immature Aedes albopictus and Toxorhynchites spp. in bamboo pots were sampled weekly. Populations of Ae. albopictus and rainfall varied from month to month. During the heavy rainfall months of September and October 1987, larval counts of Ae. albopictus were high, between 30.8 and 49.2 larvae per week compared to 16 larvae per week during the low rainfall month of January 1988. A higher population of Toxorhynchites spp. was associated with a low population of the vector.
Sarawak, on the island of Borneo, is known internationally for its rich rain forests, flora and fauna. Its rain forests, occupying two-thirds of its geographical area shelters 2500 tree species, 5500 flowering plants and over 20 000 different kinds of animals and insects. Such abundance of plants, and in particular, in the variety thereof, have attracted the attention of scientists involved in the field of research into their potential medicinal value. Recent discovery that two species of Calophyllum tree in the rain forests of Sarawak produce active anti-HIV agents, has, no doubt, intensified interest in the State's plant resources for scientific research.
Mariculture in Southeast Asia began in the 1970s and expanded rapidly during the 1980s, with the commercial hatchery production of the seabass Lates calcarifer. Other important cultured species were Epinephelus coioides, Epinephelus malabaricus, Lutjanus johni, and Lutjanus argentimaculatus. Intensification in the polyculture of these species and the large-scale international movement of fingerlings or juveniles, as well as the rapid expansion and concentration of fish farms, have caused severe problems resulting from parasitic infections. Infections in maricultured fish are predominantly caused by monoxenous parasites, in particular the capsalid and diplectanid monogeneans. Heteroxenous blood parasites also successfully maintained transmission in the culture system despite their requirement for an intermediate host. Prophylactic chemical treatments helped to reduce parasitic infection but did not eliminate them and once introduced into the floating netcage culture system, these parasites managed to maintain their transmission successfully. Despite the current lack of information regarding the biology of many parasites affecting cultured marine fishes, it nevertheless is possible to develop methodologies to produce an integrated health management system specifically designed to the needs of the mariculture practiced in the Southeast Asian region. This system is important and should include a sequence of prophylaxes, adequate nutrition, sanitation, immunization and an effective system of marketing for farmed fishes.
Space use and activity patterns by 3 species of small mammals, namely, Tupaia glis, Callosciurus notatus and e. nigrovitatus were determined. The home range size of T. glis ranged from 9,544 to 73,470m2, C. notatus from 6,512 to 16,150m2 and C. nigrovitatus 10,970m2. There was no overlap in the ranges between individuals of the same species and sex but the ranges of different species overlapped. There was no significant difference in the mean daily distance moved among the studied individuals. All individuals showed a bimodal type of activity pattern.
Penggunaan habitat dan corak aktiviti 3 spesies mamalia kecil, Tupaia glis, CalJosciurus notatus dan C. nigrovitatus telah ditentukan. Saiz banjaran kediaman T. glis adalah antara 9,544 hingga 73,470m2, C. notatus daripada 6,512 hingga 16,150m2 dan C. nigrovitatus 10,970m2. Pertindihan banjaran tidak wujud antara spesies atau jantina yang sama. Walau bagaimanapun, berlaku pertindihan banjaran antara spesies yang berbeza. Tiada perbezaan bererti pada purata jarak yang dilalui setiap hari antara individu-individu yang dikaji. Semua individu yang dikaji menunjukan corak aktiviti jenis bimodal.
Heavy metals in the aquatic environment have to date come mainly from naturally occurring geochemical materials. However, this has been enhanced by human activity such as gold mining in the case of heavy metal pollution in Sg Sarawak Kanan. The high suspended solid loads in the river have quite efficiently removed most soluble metals from the water and trapped them in the bottom sediment. Three freshwater mollusc species were collected at the point source of the heavy metal pollutants and analysed for the heavy metal contents in their tissues and shells. Two of the mollusc species (Brotia costula and Melanoides tuberculata) are purely freshwater species while the Clithon sp. nr retropictus is able to survive in fresh and brackish water environments. The Brotia costula and the Clithon sp. are the edible species which are sold in the market. Accumulation of As, Cu, Fe, Se and Zn in all the three mollusc species were determined and the level of As in the tissues of Brotia costula and the Clithon sp. was much higher than the permissible level for human consumption. The mollusc species also demonstrated different preferences for the uptake of different metals. Variations in the heavy metal contents in the shell and tissues of the same species were also observed.
The diversity of monogeneans from Southeast Asia was examined using information from the literature to show their diversity at different taxonomic (subclass, family, genera, species) levels. Knowledge of monogeneans is still incomplete in Southeast Asia and the present numbers of monogeneans are likely an underestimate of what is present on/in aquatic organisms in the region, since so few hosts have been examined. An estimate of the possible numbers of monogeneans that could be present on/in fishes and turtles in Peninsular Malaysia indicates that only 8% of the monogeneans are presently known. Analysis of the available data on monogenean diversity (or species richness) at different taxonomic levels will provide useful information on their distribution patterns. There is an uneven distribution of investigations on this topic and Malayan fauna is considered to be representative of the Southeast Asian fauna. Southeast Asian (Sundaland) monogeneans are related (at the generic level) to the monogenean fauna of South China, India and Africa.
The effects of population pressure on agricultural sustainability in the delicate tropical and subtropical ecosystems have often been thought to explain high prevalence rates of malnutrition in rural South-East Asia. However, recent studies in rural Sarawak suggest that processes of modernisation have resulted in increased variations in energy nutritional status in adults. A contributory factor may be consumption of the areca nut (Malay pinang, of the palm Areca catechu). This is thought to influence energy balance through effects on appetite and resting metabolic rate. Body mass index (BMI, kg/m2) data for 325 Iban men and 438 non-pregnant Iban women, measured in 1990 and again in 1996, have been analysed in relation to areca use, smoking behaviour, socio-economic status, and reported morbidity. Body composition derived from skinfold thickness measurements for 313 men and 382 women was also analysed. The results suggest that use of areca nut is associated with significantly lower age-related increments in BMI and percentage body fat in women after allowing for age, smoking, reported morbidity, and confounding socio-economic factors. Therefore, the impact of recent economic and social development seen in rising prevalences of 'over-nutrition' may be modulated by use of the areca nut.
Quadrat-based analysis of two rainforest plots of area 50 ha, one in Panama (Barro Colorado Island, BCI) and the other in Malaysia (Pasoh), shows that in both plots recruitment is in general negatively correlated with both numbers and biomass of adult trees of the same species in the same quadrat. At BCI, this effect is not significantly influenced by treefall gaps. In both plots, recruitment of individual species is negatively correlated with the numbers of trees of all species in the quadrats, but not with overall biomass. These observations suggest, but do not prove, widespread frequency-dependent effects produced by pathogens and seed-predators that act most effectively in quadrats crowded with trees. Within-species correlations of mortality with numbers or biomass are not found in either plot, indicating that most frequency-dependent mortality takes place before the trees reach 1 cm in diameter. Stochastic effects caused by BCI's more rapid tree turnover may contribute to a larger variance in diversity from quadrat to quadrat at BCI, although they are not sufficient to explain why BCI has fewer than half as many tree species as Pasoh. Finally, in both plots quadrats with low diversity show a significant increase in diversity over time, and this increase is stronger at BCI. This process, like the frequency-dependence, will tend to maintain diversity over time. In general, these non-random forces that should lead to the maintenance of diversity are slightly stronger at BCI, even though the BCI plot is less diverse than the Pasoh plot.
Investigations of land management impacts on hydrology are well developed in South-East Asia, having been greatly extended by national organizations in the last two decades. Regional collaborative efforts, such as the ASEAN-US watershed programme, have helped develop skills and long-running monitoring programmes. Work in different countries is significant for particular aspects: the powerful effects of both cyclones and landsliding in Taiwan, the significance of lahars in Java, of small-scale agriculture in Thailand and plantation establishment in Malaysia. Different aid programmes have contributed specialist knowledge such as British work on reservoir sedimentation, Dutch, Swedish and British work on softwood plantations and US work in hill-tribe agriculture. Much has been achieved through individual university research projects, including PhD and MSc theses. The net result is that for most countries there is now good information on changes in the rainfall-run-off relationship due to forest disturbance or conversion, some information on the impacts on sediment delivery and erosion of hillslopes, but relatively little about the dynamics and magnitude of nutrient losses. Improvements have been made in the ability to model the consequences of forest conversion and of selective logging and exciting prospects exist for the development of better predictions of transfer of water from the hillslopes to the stream channels using techniques such as multilevel modelling. Understanding of the processes involved has advanced through the detailed monitoring made possible at permanent field stations such as that at Danum Valley, Sabah.
Ten years' hydrological investigations at Danum have provided strong evidence of the effects of extremes of drought, as in the April 1992 El Niño southern oscillation event, and flood, as in January 1996. The 1.5 km2 undisturbed forest control catchment experienced a complete drying out of the stream for the whole 1.5 km of defined channel above the gauging station in 1992, but concentrated surface flow along every declivity from within a few metres of the catchment divide after the exceptional rains of 19 January 1996. Under these natural conditions, erosion is episodic. Sediment is discharged in pulses caused by storm events, collapse of debris dams and occasional landslips. Disturbance by logging accentuates this irregular regime. In the first few months following disturbance, a wave of sediment is moved by each storm, but over subsequent years, rare events scour sediment from bare areas, gullies and channel deposits. The spatial distribution of sediment sources changes with time after logging, as bare areas on slopes are revegetated and small gullies are filled with debris. Extreme storm events, as in January 1996, cause logging roads to collapse, with landslides leading to surges of sediment into channels, reactivating the pulsed sediment delivery by every storm that happened immediately after logging. These effects are not dampened out with increasing catchment scale. Even the 721 km2 Sungai Segama has a sediment yield regime dominated by extreme events, the sediment yield in that single day on 19 January 1996 exceeding the annual sediment load in several previous years. In a large disturbed catchment, such road failures and logging-activity-induced mass movements increase the mud and silt in floodwaters affecting settlements downstream. Management systems require long-term sediment reduction strategies. This implies careful road design and good water movement regulation and erosion control throughout the logging process.
Changes in species composition in two 4-ha plots of lowland dipterocarp rainforest at Danum, Sabah, were measured over ten years (1986-1996) for trees > or = 10 cm girth at breast height (gbh). Each included a lower-slope to ridge gradient. The period lay between two drought events of moderate intensity but the forest showed no large lasting responses, suggesting that its species were well adapted to this regime. Mortality and recruitment rates were not unusual in global or regional comparisons. The forest continued to aggrade from its relatively (for Sabah) low basal area in 1986 and, together with the very open upper canopy structure and an abundance of lianas, this suggests a forest in a late stage of recovery from a major disturbance, yet one continually affected by smaller recent setbacks. Mortality and recruitment rates were not related to population size in 1986, but across subplots recruitment was positively correlated with the density and basal area of small trees (10-< 50cm gbh) forming the dense understorey. Neither rate was related to topography. While species with larger mean gbh had greater relative growth rates (rgr) than smaller ones, subplot mean recruitment rates were correlated with rgr among small trees. Separating understorey species (typically the Euphorbiaceae) from the overstorey (Dipterocarpaceae) showed marked differences in change in mortality with increasing gbh: in the former it increased, in the latter it decreased. Forest processes are centred on this understorey quasi-stratum. The two replicate plots showed a high correspondence in the mortality, recruitment, population changes and growth rates of small trees for the 49 most abundant species in common to both. Overstorey species had higher rgrs than understorey ones, but both showed considerable ranges in mortality and recruitment rates. The supposed trade-off in traits, viz slower rgr, shade tolerance and lower population turnover in the understorey group versus faster potential growth rate, high light responsiveness and high turnover in the overstorey group, was only partly met, as some understorey species were also very dynamic. The forest at Danum, under such a disturbance-recovery regime, can be viewed as having a dynamic equilibrium in functional and structural terms. A second trade-off in shade-tolerance versus drought-tolerance is suggested for among the understorey species. A two-storey (or vertical component) model is proposed where the understorcy-overstorey species' ratio of small stems (currently 2:1) is maintained by a major feedback process. The understorey appears to be an important part of this forest, giving resilience against drought and protecting the overstorey saplings in the long term. This view could be valuable for understanding forest responses to climate change where drought frequency in Borneo is predicted to intensify in the coming decades.
A synthesis is presented of sampling work conducted under a UK government-funded Darwin Initiative grant undertaken predominantly within the Danum Valley Conservation Area (DVCA), Sabah, East Malaysia. The project concerned the assemblage structure, gas physiology and landscape gas fluxes of termites in pristine and two ages of secondary, dipterocarp forest. The DVCA termite fauna is typical of the Sunda region, dominated by Termes-group soil-feeders and Nasutitermitinae. Selective logging appears to have relatively little effect on termite assemblages, although soil-feeding termites may be moderately affected by this level of disturbance. Species composition changes, but to a small extent when considered against the background level of compositional differences within the Sunda region. Physiologically the assemblage is very like others that have been studied, although there are some species that do not fit on the expected body size-metabolic rate curve. As elsewhere, soil-feeders and soil-wood interface-feeders tend to produce more methane. As with the termite assemblage characteristics, gross gas and energy fluxes do not differ significantly between logged and unlogged sites. Although gross methane fluxes are high, all the soils at DVCA were methane sinks, suggesting that methane oxidation by methanotrophic bacteria was a more important process than methane production by gut archaea. This implies that methane production by termites in South-East Asia is not contributing significantly to the observed increase in levels of methane production worldwide. Biomass density, species richness, clade complement and energy flow were much lower at DVCA than at a directly comparable site in southern Cameroon. This is probably due to the different biogeographical histories of the areas.
Dynamics of the Pasoh forest in Peninsular Malaysia were assessed by drawing a comparison with a forest in Panama, Central America, whose dynamics have been thoroughly described. Census plots of 50 ha were established at both sites using standard methods. Tree mortality at Pasoh over an eight-year interval was 1.46% yr(-1) for all stems > or = 10 mm diameter at breast height (dbh), and 1.48% yr(-1) for stems > or = 100 mm dbh. Comparable figures at the Barro Colorado Island site in Panama (BCI) were 2.55% and 2.03%. Growth and recruitment rates were likewise considerably higher at BCI than at Pasoh. For example, in all trees 500-700 mm in dbh, mean BCI growth over the period 1985-1995 was 6 mm yr(-1), whereas mean Pasoh growth was about 3.5 mm yr(-1). Examining growth and mortality rates for individual species showed that the difference between the forests can be attributed to a few light-demanding pioneer species at BCI, which have very high growth and mortality; Pasoh is essentially lacking this guild. The bulk of the species in the two forests are shade-tolerant and have very similar mortality, growth and recruitment. The Pasoh forest is more stable than BCI's in another way as well: few of its tree populations changed much over the eight-year census interval. In contrast, at BCI, over 10% of the species had populations increasing or decreasing at a rate of >0.05 yr(-1) compared to just 2% of the species at Pasoh). The faster species turnover at BCI can probably be attributed to severe droughts that have plagued the forest periodically over the past 30 years; Pasoh has not suffered such extreme events recently. The dearth of pioneer species at Pasoh is associated with low-nutrient soil and slow litter breakdown, but the exact mechanisms behind this association remain poorly understood.
Community resistance to, and resilience from, perturbation will determine the trajectory of recovery from disturbance. Although selective timber extraction is considered a severe disturbance, fish communities from headwater streams around Danum Valley Field Centre, Sabah, Malaysia, showed few long-term changes in species composition or abundance. However, some species showed short-term (< 18 months) absence or decrease in abundance. These observations suggested that both resistance and resilience were important in maintaining long-term fish community structure. Resistance to perturbation was tested by monitoring fish communities before and after the creation of log-debris dams, while resilience was investigated by following the time-course of recolonization following complete removal of all fish. High community resistance was generally shown although the response was site-specific, dependent on the composition of the starting community, the size of the stream and physical habitat changes. High resilience was demonstrated in all recolonization experiments with strong correlations between pre- and post-defaunation communities, although there was a significant difference between pool and riffle habitats in the time-course of recovery. These differences can be explained by the movement characteristics of the species found in the different habitats. Resilience appeared to be a more predictable characteristic of the community than resistance and the implications of this for ensuring the long-term persistence of fish in the area are discussed.
Climatic records for Danum for 1985-1998, elsewhere in Sabah since 1879, and long monthly rainfall series from other rainforest locations are used to place the climate, and particularly the dry period climatology, of Danum into a world rainforest context. The magnitude frequency and seasonality of dry periods are shown to vary greatly within the world's rainforest zone. The climate of Danum, which is aseasonal but subject, as in 1997-1998, to occasional drought, is intermediate between less drought-prone north-western Borneo and the more drought-prone east coast. Changes through time in drought magnitude frequency in Sabah and rainforest locations elsewhere in South-East Asia and in the Neotropics are compared. The 1997-1998 ENSO-related drought event in Sabah is placed into a historical context. The effects of drought on tree growth and mortality in the tropics are assessed and a model relating intensity and frequency of drought disturbance to forest structure and composition is discussed.