Latto and Hassell (1987) disagree with the conclusion of Den Boer (1986), that the winter moth population at Wytham Wood, studied by Varley and Gradwell, was not regulated. They attempt to ...demonstrate regulation by means of a simulation model. In the present paper the validity of this model is tested step by step. The fixing of the initial and final densities, as practised by Den Boer and rejected by Latto and Hassell, did not prevent population explosions and extinctions, as was assumed by Latto and Hassell. It is shown that the deterministic formulation of the density dependence of pupal predation, as used by Latto and Hassell, deviates systematically from the field data. Replacing the values of the key-factor (k1) by random values drawn from a normal distribution (Latto and Hassell) affects the dynamics such that the ability of pupal predation to govern density is improved in the model. Changing mortalities other than the key-factor does not significantly influence the pattern of fluctuations nor the limits of density. Models should leave intact the essentials of the reality under study, while removing distracting elements (Levins 1968). As both the timing of the key-factor, and its correlation with pupal predation are essential features of the winter moth population at Wytham Wood between 1950 and 1968, the model of Latto and Hassell does not apply to this population. By simply changing log10(eggs/female) it is shown that the power of the density dependence of pupal predation to govern possible trends in density of the winter moth population at Wytham Wood is weak. On the other hand, the model of Latto and Hassell gives insight into the conditions that might favour regulation of numbers. Although the model of Poethke and Kirchberg (1987) preserves more features of the pertinent winter moth population than that of Latto and Hassell (1987) it still deviates in one essential aspect: the succession in time of both the (coupled) mortalities and the deviations from the deterministic density dependence are taken at random. Therefore, also this model is still too far from the field population to be a sound base for the statistical speculation proposed by Poethke and Kirchberg.
From 1978 to 1980,two population of Henosepilachna niponica feeding on wild thistle (Cirsium spp.) were studied in different habitats, Sawai and Kashio at Ohshika village, Nagano Prefecture, by ...construction of life tables and mark-recapture of adults. The life histories of the two populations were seasonally synchronous with the phenology of the host plant and population densities never reached a level where food shortage occurred. Both populations were characterized by high mortality(95-97%)during the immature stages due to egg cannibalism by adults, and predation by polyphagous arthropods on eggs, larvae and pupae. The reproductive rate(=no. of newly emerged females per overwintered female)during the three-year study period was low in both populations, that in Sawai(0.9-1.8)being more stable than that in Kashio(1.3-5.4). According to key factor analysis, the variation in number of eggs laid per female was the major factor responsible for the variation in reproductive rate seen in Sawai. No clear tendencies were evident in Kashio. The reason for this difference in variation pattern between the two population was obscure. The variation in number of eggs laid per female also seemed to play an important role in stabilizing population densities in both populations.
Provider: Czech digital library/Česká digitální knihovna - Institution: Academy of Sciences Library/Knihovna Akademie věd ČR - Data provided by Europeana Collections- Development and survival of ...larvae of two predatory ladybird species, Harmonia axyridis (Pallas) and Coccinella septempunctata L. on hibiscus (Hibiscus syridis L.) trees was followed daily outdoors during four seasons. Data were analysed and stage-specific mortality in a stage-structured model was estimated using Manly's (1997) method. Subsequently, key factor analysis was used to determine the life stages in which the daily mortality was best correlated with the total mortality during larval life. Consistently with the results from the first two years, the larvae suffered the greatest mortality during the first and fourth instars. The k-values for these two instars were also best correlated with those for the whole larval life, especially in H. axyridis.- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
An analysis of observations on modifications during aging of the characteristics of chromosomes during the mitotic cycle of their mutations and unscheduled aging leads to the conclusion that enhanced ...heterochromatinization during aging prevents the action of reparative enzymes, and results in increased numbers of cells with chromosomal aberrations.
Electric arc is a especial switching apparatus's phenomenon in switching loop current, reliability and using life of apparatus can be directly influenced by time of arcing, which is considered as the ...important index of switching apparatus. According to the time of apparatus arcing, we can divide it into different grades. Factors that influence the time of apparatus arcing include material, design, techniques, operation, power, equipment and circumstance. Selecting all these factors as sample, using the time of apparatus arcing to determine the sample type, we can extract the key factor using FICSEM in the same type samples, and can obtain the factor combination that achieve the same apparatus arcing time. We can improve the product quality by improving the key factor, and can reduce the product cost by using the optimal factor combination. So we can evade producing risks and can improve economy benefits.
PDF
