Food and predation as major factors limiting two natural populations of Daphnia cucullata Sars

A detailed analysis of two euplanktonic populations carried out in the same period, 18 May–11 August, 1978, in two neighboring Mazurian lakes revealed different patterns of changes in population densities and significant differences in fecundity, age structure and mean sizes of individuals despite similar epilimnion temperatures in the lakes. Similar densities were maintained in both populations although food limitation was less important and predation more intense in one than in the other of the two lakes. The relative importance of food limitation and predation is discussed in lakes of low and high fertility. It is also suggested that both low food concentration and high selective predation pressure favors small clutch sizes in cladocerans.     

The influence of thyroxine on the host-parasite relationship of Ancylostoma caninum in swiss albino mice

Bhai Ismail and Pandey A.K. 1981. The influence of thyroxine on the host-parasite relationship of Ancylostoma caninum in Swiss albino mice. International Journal for Parasitology11: 377–379. Thyroxine treatment, 1μg/0.3 ml saline/mouse/day for 21 days, significantly increased the susceptibility of female mice (P > 0.001) but not of males to Ancylostoma caninum infection, compared with their saline-treated controls. This accounted for the loss of the sex difference between the worm populations of male and female mice (0.001 < P < 0.005). More hyperthyroid females died following infection with A. caninum than control female mice. The possible reasons for higher susceptibility of female mice are discussed.     

Heliothis zea larval mortality time from topical and per os dosages of Nomuraea rileyi conidia

Heliothis zea larval mortality time was established for topical applications and per os (feeding) with fungal conidia of Nomuraea rileyi. The 6-to 7-day-old larvae received per os dosages ranging from 6 × 10⁶ to 9 × 10⁹ and a topical dosage of ca. 1 × 10⁹. These spore loads initiated fungal infections in larvae resulting in 1.5–100% accumulated mortality during the 30-day testing periods. The data indicated that regardless of the larval treatment method (topical or per os), or conidial dosage rates, the larval mortality time was never shorter than 5 days post-treatment, nor longer than 22 days. The highest percentage of larval deaths occurred from 7 to 9 days with a maximum mortality at 8 days.     

STRUCTURE AND DYNAMICS OF A POPULATION OF PALMARIA PALMATA (RHODOPHYTA) IN NORTHERN SPAIN1

Palmaria palmata (Linnaeus) O. Kuntze (Rhodophyta, Palmariaceae) is a seaweed commercially harvested for human consumption. Its population density, size structure, and frond dynamics were investigated from May 1999 to May 2001 at one intertidal locality in the northern coast of Spain, which is within the southern distributional boundary of the species in the eastern Atlantic coasts. The effect of size, age, and the life‐history phase (haploid vs. diploid) on frond growth and mortality were also evaluated. The study was carried out by mapping and monitoring fronds in the field. New fronds (macroscopic recruits or sprouts) appeared in spring, but subsequent mortality of these young fronds and detachment of the host plant led to lower density values in January. Palmaria palmata exhibited a distinctive seasonal growth cycle, with positive net growth from March to August and breakage from August to March. Interannual differences were also detected, with higher net growth in 2000 than in 1999. Net growth was apparently independent of age, reproductive status (fertile vs. reproductive), and life‐history phase (haploid vs. diploid) but was dependent on size, as longer fronds showed minor growth or greater breakage than small ones. Mortality, on the other hand, was more dependent on age than on size in the period analyzed (March–May 2000). Results of the study indicate that both size and age should be included as state variables and temporal changes in transition probabilities considered in the development of demographic models of the species.     

Environmental cadmium exposure, adverse effects and preventive measures in Japan

In Japan the most heavily cadmium (Cd)-polluted region is the Jinzu river basin, where Itai-itai disease is endemic and the Kakehashi river basin is the second most polluted region.. The village average Cd concentrations in rice were distributed in the range between 0.02 microg/g and 1.06 microg/g in the Jinzu river basin and 0.11 microg g and 0.67 microg g in the Kakehashi river basin. Severe renal damage has occurred widely in the Jinzu river basin. Even after Cd exposure had ceased, renal dysfunction became worse. Dose-response relationships between Cd exposure and health effects were clearly demonstrated in both regions. The allowable limits (according to the present authors' assessment) of Cd concentrations in rice were estimated to be 0.08 microg g to 0.13 microg g and approximately 2 g for total Cd intake. Renal dysfunction caused by exposure to Cd was associated with an increased mortality in both regions. The increased total Cd intake and high concentration of Cd in rice also exerts an adverse influence on life prognosis.     

Relative toxicity of phosphine against the bean bruchid Acanthoscelides obtectus (Say) (Col., Bruchidae)

Abstract:  The toxicity of phosphine against adult Acanthoscelides obtectus (Say) was studied over a range of concentrations, viz. 0.01, 0.0125, 0.015, 0.02, 0.04, 0.08, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 mg/l and exposure periods, viz. 0.25, 0.50, 1, 2, 6, 12, 24 and 48 h at 25°C and 65% relative humidity . Results show that both the parameters exhibited significant effects on the mortality of A. obtectus . Data indicate that 100% mortality only occurred in A. obtectus when 1-, 2- and 12-h exposure times were involved in the respective highest individual ct product. The ct products decreased as the exposure times increased for both the mortality levels of 50 and 99%. The minimum ct products for 50 and 99% kill were 0.19 and 0.29 mg h/l, respectively, at an exposure of 12 h. The influence of thresholds on regression equations of the form c ⁿ t  =  k were 0.59 and 13.80 (mg/l) ⁿ h for the fixed concentration for 50 and 99% mortality levels, respectively while they were 0.45 and 12.45 (mg/l) ⁿ h for the six exposure periods for the same mortality levels.     

Stand Biomass and Tree Mortality from Permanent Forest Plots on Krakatau,Indonesia, 1989–19951

Forest closure on the three original Krakatau Islands (Panjang, Rakata, and Sertung) took place ca 1930, about 50 yr after the apparent sterilization of the islands due to volcanic eruptions. Two permanent forest plots were established on each of these islands in 1989. A full enumeration of these plots, of two additional Rakata plots, and of two “mainland”plots from the Ujung Kulon National Park, West Java, was undertaken in 1992. These data provide the first estimates of aboveground biomass from Krakatau. The values reported for Krakatau are below the local West Javan figures, with considerable variation occurring within the islands. In 1992, the fourth Krakatau island, Anak Krakatau, began an eruption sequence which continued through the study period, depositing ash on the study sites of Panjang and Sertung. A further partial survey of these plots in 1994–1995 revealed a significant increase in mortality since the volcanic activity recommenced, with an increase in deaths of larger stems. Although Rakata has not been influenced directly by volcanism, three sites surveyed on Rakata in 1994–1995 have experienced increased tree mortality, in two cases as a consequence of storm damage and in particular, of lightning strikes. Stand dynamics on Krakatau thus appear to be strongly influenced by episodic environmental disturbance with varying degrees of dependence on the volcanic activity of Anak Krakatau.     

Soil Characteristics and Vegetation Structure in a Heavily Deteriorated Mangrove Forest in the Caribbean Coast of Colombia

Mass mortality and biomass of mangrove trees are related to soil factors in the Caribbean Coast of Colombia. Soil properties measured were particle size distribution, bulk density, organic matter, total nitrogen, total phosphorus, pH, redox potential, salinity, and extractable nitrogen (NO₂, NO₃, NH₄) and phosphorus (PO₄). Sampling was performed at three locations along two 50 m transects at each site. Soil nutrient concentrations of either exchangeable nitrogen or phosphorus were comparable to other reported values. Redox potentials (E_h) were variable probably due to microtopographic conditions and to the amount of water and organic matter present in the soil. Hydrogen potentials (pH) are within the range reported as normal for mangrove soils. Locations with highest biomass had an average soil salinity of 35 with a range of 20 to 53. Sites with dead or dwarfed vegetation had an average soil salinity of 74 and minimum and maximum values observed were 52 and 100 respectively. Statistical analysis exhibited temporal and spatial differences in soil salinity and suggest that this parameter is most correlated to the development and distribution of mangrove vegetation in the area indicating that basal area and biomass volume are inversely correlated with soil salinity.     

MORTALITY PLATEAUS AND THE EVOLUTION OF SENESCENCE: WHY ARE OLD-AGE MORTALITY RATES SO LOW?

Age-specific mortality rates level off far below 100% at advanced ages in experimental populations of Drosophila melanogaster and other organisms. This observation is inconsistent with the equilibrium predictions of both the antagonistic pleiotropy and mutation accumulation models of senescence, which, under a wide variety of assumptions, predict a “wall” of mortality rates near 100% at postreproductive ages. Previous models of age-specific mortality patterns are discussed in light of recent demographic data concerning late-age mortality deceleration and age-specific properties of new mutations. The most recent theory (Mueller and Rose 1996) argues that existing evolutionary models can easily and robustly explain the demographic data. Here we discuss the sensitivity of that analysis to different types of mutational effects, and demonstrate that its conclusion is very sensitive to assumptions about mutations. A legitimate resolution of evolutionary theory and demographic data will require experimental observations on the age-specificity of mutational effects for new mutations and the degree to which mortality rates in adjacent ages are constrained to be similar (positive pleiotropy), as well as consideration of redundancy and heterogeneity models from demographic theory.