Germination ecology of drupelets of the fig (Ficus carica L.)

Abiotic and biotic factors and their effects on germination of fig drupelets were studied. The drupelets germinated between 10^oC and 30^oC.Constant humidity was necessary for germination and frequent drying out of the substrate was unfavourable. Total darkness for the whole duration of the experiments had a slighly negative effect on germination. The fastest germination occurred at constant humidity and an alternating temperature of 20/30^oC with exposure to light for 8 hours (at the higher temperature) and to darkness for 16 hours (at the lower temperature).Natural or artificial removal of drupelets from the syconium guaranteed a high germination percentage, whereas no germination occurred in drupelets left inside the syconium. Hence birds and mammals act as dispersal agents and mediators of germination. As they eat pieces of fig syconium, they free the drupelets from the flesh, eliminating the effect of inhibitors and/or microenvironments with high osmotic pressure inside the syconium. These findings support the hypothesis that germination occurs in autumn or spring depending on the climatic zone in which the species grows.     

Interactions of colonisation density and leaf environments on survival of Trioza eugeniae nymphs

1. Female eugenia psyllids Trioza eugeniae oviposit on the margins of expanding young Syzygium paniculatum leaves. The developing nymphs, feeding within pit‐shaped galls on the leaves, cause the leaves to become curled and deformed. The degree of leaf curling was correlated positively with densities of T. eugeniae nymphs. 2. High relative humidity increased persistence of nymphs on leaves at low insect densities, but persistence did not differ between high or low relative humidity conditions when nymphal densities were high and leaves were greatly curled. 3. Direct insolation increased nymphal mortality. Nymphs on the abaxial leaf surface in the direct sun had lower mortality than similarly exposed nymphs on the adaxial leaf surface. 4. Field populations showed high preference for abaxial leaf surfaces and a stronger preference for shaded adaxial surfaces than for exposed adaxial surfaces. 5. Adverse environmental conditions of direct insolation and low relative humidity may be mitigated by leaf curl associated with moderate populations, however competition at high nymphal density supersedes any potential benefit arising from leaf curling and has a negative effect on nymphal survival.     

The contribution of abiotic processes to buried litter decomposition in the northern Chihuahuan desert

Summary Creosobebush (Larrea tridentata) fine litter was treated with either the general biocide HgCl₂ and CuSO₄ or water (controls) and buried 5 cm beneath the soil surface in the northern Chihuahuan Desert. The treated litter showed significantly less mass loss than controls during the three month summer-autumn field study; controls lost about 20% of the original mass while treated litter lost less than 2%. In addition, the total nitrogen content of the control litter increased from an initial concentration of about 14.08 g kg^-1 to 17.62 g kg^-1 dry weight by the end of the study, while treated litter nitrogen content decreased to 13.30 g kg^-1. Results suggest abiotic processes other than leaching have little effect on the decomposition of buried litter in this environment.     

Oscillations in a system with material cycling

We study a system of two integrodifierential equations which models the evolution of a biotic species feeding on an abiotic resource. We also consider nutrient recycling with time delay. By Hopf bifurcation theory we prove the existence of stable oscillations for a range of values of the input of nutrients.Work performed within the activity of the research group Evolution Equations and Physico-Mathematical Applications, M.P.I. (Italy), and under the auspices of G.N.F.M., C.N.R. (Italy)     

Differences in low pH tolerance among closely related sunfish of the genus Enneacanthus

Synopsis Three closely related sunfish in the genus Enneacanthus were examined to determine if differences existed in their tolerance to low pH that could explain their contrasting distributions. Na fluxes of E. obesus, E. gloriosus, and E. chaetodon were measured during 12 h exposure to pH 4.0 and 3.5 (all species), and 3.25 (former 2 species only). All experienced ionic disturbances upon acid exposure resulting from inhibition of active Na influx and stimulation of passive Na efflux, but E. gloriosus and E. chaetodon experienced greater disturbances than E. obesus at all pH's tested. Body and plasma Na concentrations of E. gloriosus were measured after one week of exposure to a range of pH's for comparison with previously published data from E. obesus. Exposure to pH 4.0 and below caused a depression in body and plasma Na concentration of E. gloriosus, and only two of 10 fish survived the one week test period at pH 3.5; none survived at pH 3.25. In contrast, exposure to pH 4.0 for five weeks had no effect on body Na concentration of E. obesus, all 10 fish survived exposure to pH 3.5 for two weeks. Growth of E. gloriosus and E. obesus were measured separately during 12 weeks of exposure to a range of pH's. E. gloriosus exposed to pH 4.25 and 4.0 grew at a lower rate than those at higher pH's (4.5, 5.0, and 5.8), and body Na concentrations of fish at pH's 4.25 and 4.0 were significantly less than the others. With declining pH E. obesus did not exhibit reduced growth until pH 3.75 was reached; no depression in body Na concentration occurred at this pH. These results show that there are marked differences in low pH tolerance among closely related species of Enneacanthus which could affect their distributions and competitive interactions.     

桑树磷脂酶MaPLA1-2D亚型4个基因的克隆与胁迫应答分析

磷脂酶(phospholipase)是一类在植物生长发育和胁迫应答中起重要调控作用的磷脂水解酶,也是一类重要的信号转导酶。而磷脂酶A1(PLA1)在植物应答生物胁迫和非生物胁迫中的功能研究鲜见报道。研究从桑树(Morus alba L.)中克隆了磷脂酶PLA1的1个亚型MaPLA1-2D基因,对其进行了序列分析、组织表达、胁迫诱导表达和蛋白亚细胞定位分析。结果表明,桑树PLA1-2D亚型基因包括4个成员,命名为MaPLA1-2D.1~MaPLA1-2D.4。4个基因在桑树根和叶中高水平表达,蛋白亚细胞定位在叶绿体。序列和进化分析表明MaPLA1-2D基因4个成员与拟南芥AtDAD1基因的保守结构域序列具有较高相似度且进化关系紧密。MaPLA1-2D基因4个成员的启动子含有多种胁迫应答顺式元件和激素响应元件;胁迫诱导表达模式分析表明MaPLA1-2D基因表达受干旱和脱落酸处理显著诱导。以上结果说明,MaPLA1-2D基因与拟南芥DAD同源,可能在桑树非生物胁迫应答中发挥重要功能。     

The life histories and population dynamics of two carabid species on a Dutch heathland

Summary We deal with the causes of the synchronously fluctuating numbers of subpopulations of the carabid species Calathus melanocephalus as compared with the asynchronously fluctuating numbers of subpopulations of the carabid Pterostichus versicolor. Both species continuously occupy a large heath area, Dwingelder Veld (1600 ha), in The Netherlands, and are studied there in the same localities with the same methods. Of the adults of C. melanocephalus, 90% do not cover more than 2 ha during the entire reproductive season, while 90% of adults of P. versicolor cover no more than 12 ha. In C. melanocephalus egg production in the field is usually similar to that under optimal feeding conditions in the laboratory, but in P. versicolor egg production seems to be much lower in the field. In the field 70–80% of the eggs most probably are killed by eelworms, followed by more than 90% mortality among the remaining larvae. Comparing mortality of developmental stages in laboratory experiments with that in field experiments in enclosures, it appears that mortality of larvae is not density-dependent, even when density in the experiments is much higher than it ever is in the field. Larval mortality mainly results from the poor ability of the larvae to find prey, even when in field experiments prey density is increased far above natural densities. We discuss why these poor prey-finding abilities are not improved by natural selection. In the spring breeder P. versicolor differences between localities both in abiotic factors, soil moisture and surface temperature, and biotic factors, reactions of prey species to abiotic factors, in spring and summer when the larvae are maturing contribute to the asynchronous fluctuations of numbers between subpopulations. In the autumn breeder C. melanocephalus possible differences in biotic factors between sites are outnumbered by the effects of winters with a higher or lower than normal amount of precipitation respectively. During a wet winter mortality among the larvae is much higher than during a dry winter. As these winter conditions are similar over large areas (many km²) the fluctuations of numbers between subpopulations are synchronous.Communication No. 443 of The Biological Station, Wijster     

Both facilitation and limiting similarity shape the species coexistence in dry alkali grasslands

Facilitation is an important driver of community assembly, and often overwhelms the effect of competition in stressed habitats. Thus, net effect of biotic interactions is often positive in stressed grasslands, where dominant species and litter can protect the subordinate species. Besides facilitation, niche partitioning can also support species coexistence leading to limiting similarity between subordinate species. Our aim was to provide a detailed analysis of fine-scale biotic interactions in stressed alkali grasslands. We supposed, that there are positive relationships between the main biomass fractions and species richness. We expected the expansion of trait ranges and the increase of trait dissimilarity with increasing biomass scores (total litter, green biomass of dominant species) and species richness. We studied the relationships between main biomass fractions, species richness, functional diversity and functional trait indices (ranges, weighted means and Rao indices). We used fine-scale biomass sampling in nine stands of dry alkali grasslands dominated by Festuca pseudovina. The detected relationships were always positive between the main biomass fractions (green biomass of dominant species, total litter and green biomass of subordinate species) and species richness. We found that the green biomass of dominant species and total litter increased ranges and dissimilarity of functional traits. Our results suggest that in dry alkali grasslands facilitation is crucial in shaping vegetation composition. The green biomass of dominant species and total litter increased the biomass production of subordinate species leading to overyielding. We found that mechanisms of facilitation and limiting similarity were jointly shaping the species coexistence in stressed grasslands, such as alkali grasslands.