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Abstract

Protozooplankton are dominant grazers of phytoplankton and an important component of the microbial food web, as a link between pico and nanoplankton to higher trophic levels. Their fast growing rate, relative abundance, biomass and diversity are used as indicators of organic and toxic pollution. The impact of urbanisation on ecosystems and their sustainability and biodiversity have recently been much studied. We studied the protozooplankton ciliate communities during the vegetation period from April to October in two small lakes (Bābelītis, Gaiļezers) and two reservoirs (Bolderāja, Saurieši). The largest peak of biomass (15.7 × 102 mg/l) was found in Gaiļezers Lake in August and of abundance (60.2 × 103 org/l) in Bābelītis Lake in July. The lowest biomass (0.006 mg/l) and abundance (0.12 × 103 org/l) were found in the Saurieši Reservoir station. The most abundant ciliates were from the order Oligotrichida.

Abstract

Arable soils are one of the most valuable natural resources and their long-term sustainable management is a determining factor in the integrated production of strawberries. It is well known that the current large-fruited garden strawberry (Fragaria × ananassa Duchesne ex Rozier) cultivars are more susceptible to many species of plant-parasitic nematodes and other plant pathogens. The aim of this study was to evaluate the effects of some cultural practices as potential methods for control of nematodes in the integrated production of strawberries. The investigation of the nematode populations was carried out in the region of western Balkan Mountains in Bulgaria (43°33'22.3"N 22°47'03.4"E), with cultivar ‘Maya’. In the surveyed area, plant protection products were applied under an approved scheme complying with the requirements for integrated fruit production (IOBC, IFP). Nematode populations were identified and classified to trophic level. The following genera of plant-parasitic nematodes were identified: Pratylenchus crenatus, P. neglectus, P. thornei, Tylenchorhynchus sp., and Paratylenchus spp. The density and species composition of plant parasitic nematodes were significantly reduced at the end of the study period comparing to the beginning of the study. From the results, it is clear that the integrated production can be defined as an economically feasible production of high quality fruits, giving priority to environmentally safe methods of pest control.

Dynamics , Academic Press, Boston, MA. Kuang, Y. and Takeuchi, Y. (1994). Predator-prey dynamics in models of prey dispersal in two-patch environments, Mathematical Biosciences   120 (1): 77-98. Li, K. and Wei, J. (2009). Stability and Hopf bifurcation analysis of a prey-predator system with two delays, Chaos, Solitons & Fractals   42 (5): 2603-2613. May, R. M. (1973). Time delay versus stability in population models with two and three trophic levels, Ecology   4 (2): 315-325. Prajneshu Holgate, P. (1987). A prey-predator model with switching effect, Journal of

Abstract

The control of insect pests in agriculture is essential for food security. Chemical controls typically damage the environment and harm beneficial insects such as pollinators, so it is advantageous to identify targetted biological controls. Since predators are often generalists, pathogens or parasitoids are more likely to serve the purpose. Here, we model a fungal pathogen of aphids as a potential means to control of these important pests in cereal crops. Typical plant herbivore pathogen models are set up on two trophic levels, with dynamic variables the plant biomass and the uninfected and infected herbivore populations. Our model is unusual in that (i) it has to be set up on three trophic levels to take account of fungal spores in the environment, but (ii) the aphid feeding mechanism leads to the plant biomass equation becoming uncoupled from the system. The dynamical variables are therefore the uninfected and infected aphid population and the environmental fungal concentration. We carry out an analysis of the dynamics of the system. Assuming that the aphid population can survive in the absence of disease, the fungus can only persist (and control is only possible) if (i) the host grows sufficiently strongly in the absence of infection, and (ii) the pathogen transmission parameters are sufficiently large. If it does persist the fungus does not drive the aphid population to extinction, but controls it below its disease-free steady state value, either at a new coexistence steady state or through oscillations. Whether this control is sufficient for agricultural purposes will depend on the detailed parameter values for the system.