Timing of foetal growth spurts can explain sex ratio variation in polygynous mammals

The prediction from sex ratio theory that natural selection on sexually dimorphic mammals should favour an excess of male offspring only when mothers are in good condition, has been tested extensively but with little consistency in results. Although recent studies have shown that environmental variations may cause some of the discrepancy, there have also been reports of contrasting sex ratios under similar environmental settings. Here it is suggested that variation in timing of environmental stress and sex-specific differences in foetal growth pattern in relation to maternal condition, may explain such seeming contradictions in sex ratio variation of polygynous mammals.     

Timing and rate of sexual maturation of European eel in brackish and freshwater environments

Maturation rates in three European eel Anguilla anguilla populations increased from September to October and were slightly lower in fresh water than in brackish waters. Average and variance of total length at maturation were larger in females than males.     

GROWTH RATES OF PSEUDOPEDINELLA PYRIFORME (CHRYSOPHYCEAE) IN RESPONSE TO 75 COMBINATIONS OF LIGHT,TEMPERATURE AND SALINITY1

Clonal cultures were established of single cells of Pseudopedinella pyriforme Carter isolated from the Chesapeake Bay. Axenic cultures were incubated at 5, 10 and 15 C; in 2 1/2, 5, 7 1/2, 10 and 15‰; and at 143, 285, 428, 571 and 714 μW/cm² white light. Maintainable growth rates were calculated from absorbance readings taken for 3 to 5 days from acclimated cultures. The maximum number of doublings per day was 0.9 at 2 1/2‰ salinity, 571 μW/ cm² and 15 C. A salinity of 5 ‰ produced the fastest growth at most light intensities up to 428μW/cm² and temperatures of 5, 10 and 15 C.     

Species-specific population-density thresholds in cladocerans?

The population density of a Daphnia species seems more dependent on properties specific to the species than on those specific to the point in the season, location within a lake basin or the given lake itself. In spite of week-to-week fluctuations, the population density for each of two common European Daphniaspecies was found to be remarkably similar within single lakes (from station to station on a single date, and from date to date at a single station) as well as from lake to lake, regardless of trophic state. All lakes on all dates revealed densities in the range 10–50 ind l^–1 for the smaller-bodied D. cucullata and 1–5 ind l^–1 for the larger-bodied D. hyalina, in spite of different intensity of reproduction resulting from different food levels (chlorophyll a between 0.2 and 4.2 g/l). It can be asserted that the population density of each species remains far below the carrying capacity of the habitat K, and does not depend on food levels, which merely set the rate of population increase, while the population density reflects the species' vulnerability to predation by planktivorous fish. The reactive distance (the distance over which a foraging fish can see its prey) in 1+ roach, a dominant planktivore in the lakes studied, has been found to be twice as great for D. hyalina as for D. cucullata, whatever the light intensity. The relative reactive field volume was therefore an order of magnitude greater for the former than for the latter, showing that the densities of the two prey species would be assessed by a foraging roach as equal when, in reality, they differed by an order of magnitude, as they do in various lakes and in various seasons.The first of the two conclusions is that whatever the growth and reproduction in a population of a cladoceran such as Daphnia, its density would be fixed by mortality induced by fish predation. The second would be, that the difference between the bottom-up and top-down effects in freshwater is more than merely the upward or downward direction along the food web, since the bottom-up effects are about the flow control (the rate of net production, individual growth rate, rate of reproduction) and the top-down about the standing-crop control (biomass, individual body size, population density level).     

始红蝽越冬聚集行为对其能量代谢的影响

聚集行为是动物适应不良环境的一种生态对策。始红蝽Pyrrhocoris apterus在成虫滞育越冬期间具有显著的聚集行为。采用LI-6400型光合仪测定了5种聚集度(分别用1头、5头、10头、20头和50头的群体大小表示)下始红蝽的呼吸量,通过呼吸量计算得到各聚集度始红蝽的呼吸速率(rate of respiration,Rr)及能量代谢速率(rate of metabolism,Rm),旨在明确聚集行为是否能够对始红蝽越冬时的能量代谢产生影响。结果表明： 不同聚集度间始红蝽的Rm值存在显著性差异; 并且随聚集度的增加,Rm值与聚集度呈显著负相关,Rm值依次为0.052,0.044,0.041,0.037和0.033 W/g。结果说明聚集行为可以有效降低始红蝽新陈代谢速率,有利于种群成功越冬。     

Harvest reserves reduce extinction risk in an experimental microcosm

Overharvesting by humans threatens a substantial fraction of endangered species. Reserves have recently received enormous attention as a means of better conserving harvested resources, despite limited empirical evidence of their efficacy. We used manipulated microcosms to test whether reserves reduce extinction risk in mobile populations of harvested Tetrahymena thermophila , a ciliate. Here we show that patterns of population distribution inside and outside reserves can be accurately predicted on the basis of simple models of diffusion coupled with logistic controls on local population growth. No extinctions occurred in eight experimental trials with reserves, whereas extinction occurred in seven of eight trials without reserves, as predicted by population viability models based on stochastic population processes. These results suggest that marine reserves may be an effective means of improving long-term viability in heavily harvested fish species.     

Nutrient and microbiological characteristics of fine benthic organic matter in sediment settling ponds

1. Fine benthic organic matter (FBOM, particles <1 mm) was collected eight times in 1995 and 1996 from settling ponds located at the base of five catchments, and assayed for total C, N and P, extractable ammonium, mineralisable N, organic P, labile polysaccharides, denitrification potential, acetylene reduction and respiration rates, and β‐glucosidase and phosphatase activities. The five catchments (10–101 ha in size) are located in the Pacific North‐west of the United States. They contain either old‐growth forests dominated by Douglas‐fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) or stands that were harvested 30 years ago and replanted with Douglas‐fir, with riparian zones dominated by red alder (Alnus rubra), bigleaf and vine maple (Acer macrophyllum; A. circinatum) and understory herbaceous plants. 2. C : N ratios were significantly higher, and mineralisable N, extractable ammonium and labile polysaccharides were all significantly lower, in FBOM from old‐growth catchment sediment than in FBOM from catchments containing harvested stands, showing that the chemical characteristics of FBOM were influenced by forest harvest. C and N concentrations were greatest in sediment from old‐growth catchments, but microbial activities (respiration, denitrification potential, phosphatase and β‐glucosidase) tended to be greater in sediment from the harvested catchments. 3. Levels of certain chemical components of harvested‐catchment FBOM were elevated relative to those found in old growth; specifically, organic and total P, extractable ammonium, mineralisable N and labile polysaccharides, suggesting that stream FBOM from harvested basins is more biodegradable than stream FBOM from old‐growth basins. 4. In addition to effects of past timber harvest on FBOM characteristics, there were also significant seasonal differences in both logged and unlogged catchments in all variables except mineralisable N, labile polysaccharides and acetylene reduction rates. 5. The results indicate that past timber harvest in five river basins influenced both composition of and seasonal fluctuations in fine benthic organic matter (FBOM) collected from stream sediments in settling ponds, suggesting a linkage between forest harvest and stream productivity. 6. Comparisons between seasonal patterns in stream and settling pond sediment FBOM characteristics suggested that the readily decomposable organic matter entering sediments during a storm event are rapidly transported and decomposed during their movement through the catchment basin. It also showed the validity of studying settling pond sediments as a surrogate for mountain stream sediments.     

Coevolution is linked with phenotypic diversification but not speciation in avian brood parasites

Coevolution is often invoked as an engine of biological diversity. Avian brood parasites and their hosts provide one of the best-known examples of coevolution. Brood parasites lay their eggs in the nests of other species, selecting for host defences and reciprocal counteradaptations in parasites. In theory, this arms race should promote increased rates of speciation and phenotypic evolution. Here, we use recently developed methods to test whether the three largest avian brood parasitic lineages show changes in rates of phenotypic diversity and speciation relative to non-parasitic lineages. Our results challenge the accepted paradigm, and show that there is little consistent evidence that lineages of brood parasites have higher speciation or extinction rates than non-parasitic species. However, we provide the first evidence that the evolution of brood parasitic behaviour may affect rates of evolution in morphological traits associated with parasitism. Specifically, egg size and the colour and pattern of plumage have evolved up to nine times faster in parasitic than in non-parasitic cuckoos. Moreover, cuckoo clades of parasitic species that are sympatric (and share similar host genera) exhibit higher rates of phenotypic evolution. This supports the idea that competition for hosts may be linked to the high phenotypic diversity found in parasitic cuckoos.     

THE USE OF IMMOBILIZATION IN ALGINATE BEADS FOR LONG-TERM STORAGE OF PSEUDANABAENA GALEATA (CYANOBACTERIA) IN THE LABORATORY1

A new method for long-term storage of algal cultures in the laboratory was tested. The procedure is based on the cell immobilization technique. Cells of the filamentous cyanobacterium Pseudanabaena galeata Bocher were immobilized in sodium-alginate beads and stored for 14–18 months. The structure and functional features of the organism were maintained in this immobilized state and no ultrastructural biochemical, or growth rate differences were detected between stock and previously immobilized cell cultures after this period. We discuss the advantages of this method compared to other preservation methods and recommend the use of immobilization in alginate beads for long-term algal storage.     

The effects of deforestation on wildlife along the transamazon highway

Hunting, although prohibited, is widely practiced by the rural inhabitants settled along the Transamazon highway. In 1997 and 2000, we investigated subsistence hunting in Uruará, a township located on an Amazonian pioneer front (Brazil). We analyze hunting practices, game yield, hunting efficiency and their relation to forest coverage rate. The hunting methods were stand hunting (55.5%) and beating (44.5%). Paca (Agouti paca), tatus (Dasypus novemcinctus and D. septemcinctus), and collared peccary (Pecari tajacu) were the most frequently hunted species, supplying 68% of the gross game weight. Beating was significantly more efficient than stand hunting (3 vs. 1.9 kg/hunter/h, Mann–Whitney U test, P=0.02). Hunting territories were classified in three categories according to forest coverage rate. The higher the forest coverage rate the larger was the harvested species and the more efficient the hunter (Kruskal–Wallis test P=0.01). Considering the ecological and demographic changes in this pioneer settlement, development of a viable plan for game management and forest preservation is of great importance.