One of the most important services provided by biodiversity is thought to be the biological control of pests in agricultural landscapes, including aphids on cereals. The food webs potentially contributing to biological control of aphids primarily consist of polyphagous predators, parasitoids and pathogens. The problems of aphid pests have increased greatly since the 1970-ies, possibly as an effect of agricultural intensification, which is thought to have reduced diversity and abundance of these predators and parasites and consequently their biocontrol potential. The main objective of this study was to test this by measuring this potential for biological control of aphids, and relate it to agricultural intensification and predator abundance. We selected 30 farms distributed along agricultural intensification gradients, based on the amount of fertilizers applied per hectare. Estimates of ground-living predator density were obtained using pitfall trapping over a one-week period. Traps were placed inside the cereal fields, 10 m from the margin, in 2 replicates per field. Predation risk due to ground-living predators (biocontrol potential) was estimated by monitoring removal of aphids glued to labels. This was done in the same fields, in the immediate vicinity of the traps, over a period of 2 days. The proportion of aphids eaten per unit time was the response variable. We present the correlations between intensity of agricultural exploitation, predator abundance and biocontrol potential. The outcomes are not straightforward in that intensification begets a reduction in predator density and biocontrol potential. We discuss the potential confounding issues that might have affected our results.
This study determined the effect of larval density-dependent competition for food on development and adult fitness in Sesamia nonagriodes Lef. (Lepidoptera: Noctuidae). Different numbers (5, 10, 15, 20 and 30 individuals) of larvae of the pink stalk borer were reared on a constant amount of food. Although crowding during the immature stages did not significantly increase mortality, it prolonged the larval developmental period and resulted in reduced pupal weight. Females were more adversely affected by high density than males, resulting in lighter females, indicating that female growth is more sensitive to density. The fecundity of the adults reared in the various larval crowding treatments was analysed. Total female fecundity was correlated negatively with increasing larval density. The effects of crowding on fecundity were not caused by the reduced pupal weight, indicating that food shortage during larval development may affect adult traits. Female longevity was negatively affected by density and positively related to pupal weight. Thus, larval density may affect the allocation of food resources and adult fitness. We conclude that crowding related changes during larval development directly affect larval life and reduce female fitness.
Macroptery is common in many species of Orthoptera, but the causes are still discussed. Besides the assumption that macroptery is genetically determined, there is evidence that wing dimorphism is induced by environmental factors, particularly population density. However, most of the research is on pest species. In contrast, knowledge of wing dimorphism in species that occur at low population densites is still poor. Our study aims to test how density actually affects macroptery. As model organisms we chose two bush-cricket species of the genus Metrioptera (Ensifera: Tettigoniidae): While long-winged M. roeselii (Hagenbach, 1822) occur regularly, macropterous M. brachyptera (Linnaeus, 1761) are rare and are never observed outside their mating habitat. Nymphs of populations from the range core of both species (340 individuals each) were reared in groups of three and six individuals per 500 cm3 box, and individually. Our analyses revealed that development of macropters was mainly affected by the initial rearing densities. Compared with those reared individually the number of macropters was significantly higher among individuals reared at medium and high densities. The percentage of macropterous individuals was about twice as high in M. brachyptera as in M. roeselii, and the development of macropters significantly differed between the two species. These findings lead to the conclusion that macropterism is mainly influenced by density stress in both bush-crickets. Genetically determined wing dimorphism is unlikely, otherwise the observed high numbers of long-winged individuals of M. brachyptera, which are very rare under natural conditions, would never have developed in the laboratory. Macropterous M. brachyptera may rarely be found in the field, but we argue that this is due to low natural densities and, accordingly, to rare exposure to density stress.
The influence of increasing number of mating partners on the copulatory behaviour and reproduction in Brandt’s voles (Microtus brandti) was studied. Compared with the control group of 1 ♂ + 1 ♀, our results showed when increasing only female partners, the mating opportunity was increased in males while decreased in female in the treatment group of 1 ♂ + 2 ♀♀; the mating opportunity of male and female were both decreased significantly in the treatment group of 1 ♂ + 3 ♀♀. When increasing only male partners, male mating opportunity in treatment groups 2 ♂♂ + 1 ♀ and 3 ♂♂ + 1 ♀ decreased significantly while no change was significant in females in both treatment groups. When increasing the number of male and female partners simultaneously in the treatment group of 2 ♂♂ + 2 ♀♀, the mating opportunity for both males and females was decreased significantly. Comparing with the control, the mean litter size in all five-treatment groups lessened significantly and female pregnancy rate dropped significantly if they copulated less than five times. From these results, we have demonstrated a significant reproductive interference due to mate competition in Brandt’s voles and thus, competitively reproductive interference may be an important behavioural mechanism in regulating population density in this rodent species. However, due to possible laboratory artifacts, we still need further study, especially in the field, to validate our results.
In summer 1992 through spring 1994, amphibian abundance and breeding was studied in the pristine temperate forests, typical of central European lowlands. The years 1991, 1992, and 1993 were among the driest in the recent decades, with the spring-summer precipitation 35% lower than the long-term average. In the primeval forests of Białowieża National Park, common frogs Rana temporaria spawned in small (on average, 0.2 ha) ponds (postglacial melt-out hollows) devoid of wood cover and characterised by water pH 5.1-6.0 (as measured in April). Breeding success of frogs, monitored qualitatively in 1993, was rather poor due to pond desiccation. The capture of amphibians on forest grids revealed that densities and seasonal dynamics differed between wet and drier deciduous forests. No amphibians were captured in the mixed coniferous forests during the study. In the wet ash-alder forests, on average, 39 amphibians ha-1 were recorded in late April, 12 ind ha-1 in summer, and 195–222 ind hasup-1 in autumn (September). In those forests, 90% of captured amphibians were common frogs, 6% common toads Bufo bufo, and 4% moor frogs R. arvalis. In the drier oak-lime-hornbeam forests, amphibians appeared in May, and increased in numbers towards summer (19–24 ind ha-1) and autumn (45–71 ind ha-1). Of all amphibians caught in those forests, 43% were common frogs, 38% common toads, and 19% were moor frogs. A majority of amphibians captured in autumn were young of the year. By mid-October, all amphibians had left the forest for their hibernation sites. Comparison of our data collected in very dry years with other available data from Bia∏owie ̋a Primeval Forest (various years between 1955 and 1998) revealed that summer indices of amphibian abundance were strongly positively correlated with rainfall in April-June of the census year and the previous year.
Among the programmes aimed at developing a standard model for properties and state of the Earth’s crystalline crust, those dealing with drilling the Kola (SG-3), Ural (SG-4) and German (KTB) superdeep boreholes yielded the most interesting results. No marked depth dependence of rock volume density and seismic wave velocities was observed in the sections of SG-3 and SG-4. A new result of the investigations is the discovery of strongly anisotropic rocks in the SG-3, SG-4 and KTB sections. In the massifs of the Kola and German superdeep boreholes such rocks constitute the majority of the drilled sections. The presence of the velocity anisotropy as well as the complex structure of the rocks composing crystalline metamorphosed sequences greatly hamper the interpretation of the results obtained from the seismic survey conducted at the surface., Felix F. Gobratsevich., and Obsahuje bibliografii
The common hamster (Cricetus cricetus L.) is supposed to be an abundant species in Eastern Europe including Ukraine. However, the current data on hamster’s occurrence in Ukraine from 1990 till nowadays show that the species became rare. The common hamster can be found in the West, North-East Ukraine and the Crimean peninsula. The species have declined in the forest-steppe zone and became extinct in most part of the steppe zone. Its actual distribution range has thus been strongly reduced. One of the possible causes of this decline is the habitat loss due to changes in agricultural management.
Data on the webs, prey spectrum, density and fecundity of Theridion impressum from three different habitats [fields of sunflower, fiddleneck (Phacelia), and apple trees] are presented and discussed. The volume of webs were found to vary between 5 (the first free instar) to 117 cm3 (subadult and adult specimens). The mean density of adult spiders per plant was 0.7 (sunflower), 1.5 (fiddleneck) and 1.2 (per apple branch). Spiders preferred to build webs in the upper part of vegetation or at the extremities of tree branches. The prey spectrum was assessed by collecting webs and identifying their contents. Prey items were primarily aphids (73%), Diptera (7.5%), acid Coleoptera and Hymenoptera (both 5.4%). Pests comprised 90% of the prey; the remaining 10% was accounted for by natural enemies, pollinators and other insects. The number of insects captured in webs differed among study habitats (sunflower > fiddleneck > apple tree) though this difference was not statistically significant. Due to greater numbers of aphids in webs on sunflower, the mean prey length was significantly smaller on sunflowers than in other plots. An index of fecundity was obtained by counting the number of eggs in eggsacs. This varied from 48 to 156 per eggsac and was not significantly different between study plots. The number of eggs was strongly correlated with numbers of prey captured per spider.