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Influence of the population density and the amount of food on Chironomus plumosus (L.) and Tubificidae. Laboratory experiments

Kajak Z., Prus P.

Polish Journal of Ecology

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2004

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Vol. 52, nr 1

47-53

EN

The aim of this paper has been to examine experimentally the importance of the density of larvae and of the addition of the food for Chironomus and Tubificidae using selected parameters and indices of their populations. Increase of the density of Chironomus plumosus larvae (0.5-50.0 thousands ind. m^-2) in laboratory experiments resulted in the decrease of emergence of imagos, number of tube apertures (3.5-0.4 apertures ind.^-1), and in the lower rate of tubes building. The addition of the food (powdered dry daphnids or food tablets for aquarial fish) had only slight effect on tube numbers but it decreased clearly the getting out of larvae from tubes (probably due to improved feeding conditions inside tubes). It had also a slight negative effect on the survival of larvae. Numbers and individual growth of Tubificidae were positively dependent on the addition of the food (also in the form of naturally dead Chironomus larvae) and negatively - on the density of Chironomus

2

Effects of the density of larvae and type of substrate on Chironomus plumosus L. (Diptera: Chironomidae) population. Laboratory experiments

Kajak Z., Prus P.

Polish Journal of Ecology

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2001

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Vol. 49, nr 4

369-378

EN

Strong dependence of larval tube numbers on the population density, the condition of larvae and feeding situation occurred, but no correlation with the type of substrate was found. Numbers of larval tubes per individual were on the average 2.6 times lower at high (20 and 40 thousands ind. m^-2) than at low (2 - 2.5 thousands ind. m^-2) initial densities of larvae. They fluctuated strongly, but only at low densities, indicating the very high activity of larvae; high densities probably restrained this activity. The grown up larvae succeeded in finishingtheir full development in the mineral substrate with the tiny (<0.1 mm) layer of the natural mud at the top of it. No conical nettings (inside larval tubes) for food filtration were observed. The larvae fed mostly on the internal walls of their tubes; sometimes they also collected particles from the surface of the substrate (especially of substrates poor in the organic matter), after the food was furnished. The emergence of imagines depended on the larval density but quite differently than the numbers of tubes. The threshold for the decreased tube numbers per individual was between 2.5 and 20 thousands individuals m^2, while that for the emergence of imagines - between 20 and 40 thousands individuals m^2.

3

Long-term dynamics of the bank vole Clethrionomys glareolus at Pallasjarvi, northern Finnish taiga

Henttonen H.

Polish Journal of Ecology

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2000

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Vol. 48, Suppl.

87-96

EN

The whole rodent community (eight arvicoline species) has been followed at Pallasjarvi, at the northern limit of Clethrionomys glareolus in Finnish Lapland, since 1970. Dynamics were cyclic until the mid 1980's but since then the pattern has been stable. Also the species abundances have changed. The delayed density dependence, characterising the cyclic period, is not found during the stable period. Causes for this change in cyclicity are discussed. The bank vole is the most common rodent species in forests up to its northern limit. The long-term, Year around live trapping studies and feeding experiments suggest e.g. that delayed maturation of young is not optimal but due to social constraints. Food addition resulted in higher densities, but the effect on the density-dependent structure was negligible and the dynamics were not affected by food addition.

4

Cellular Automata and Many-Particle Systems Modeling Aggregation Behavior Among Populations

Morale D.

International Journal of Applied Mathematics and Computer Science

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2000

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Vol. 10, no 1

157-173

EN

A cellular automaton model is presented in order to describe mutual interactions among the individuals of a population due to social decisions.The scheme is used for getting qualitative results, comparable to field experiments carried out on a population of ants which present an aggregative behavior. We also present a second description of a biological spatially structured population of N individuals by a system of stochastic differential equations of Ito type. A 'law of large numbers' to a continuum dynamics described by an integro-differential equation is given.

5

Species composition, coexistence and mortality factors in a carrion-exploiting community composed of necrophagous Diptera and their parasitoids (Hymenoptera)

Ulrich W.

Polish Journal of Ecology

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1999

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Vol. 47, no 1

49-72

EN

In a beech forest on limestone, the community of carrion (dead Arion ater slugs) exploiting Diptera and their parasitoids (Hymenoptera) was studied. The carcass sustained 17 species of Diptera and 12 of Hymenoptera. With the exception of Kleidotoma psiloides (Eucoilidae), all of the parasitoid species bred were polyphagous and attacked all of the fly species present. The populations of the fly and wasp species were highly aggregated. The degree of aggregation depended in an inversely manner on the density. The dispersion of the parasitoids was independent from the number of hosts. Diptera, which lay their eggs in a late stage of decay, showed a negative correlation between aggregation and the weight of the slugs. There was no interspecific competition detectable between the fly species. The parasitoids did compete markedly only at high levels of parasitism. The parasitoids showed only a weak (negative) density dependent reaction to the numeber of hosts present. The degree of density dependence was more pronounced in the more infrequent species. The total parasitoid numbers increased in a linear manner with increasing host densities, and therefore the overall parasitism rate was roughly constant for different host numbers. Large predators and necrophages (Silphidae, Carabide, Arion ater) had a high impact on the mortality of the flies and wasps. in experimental boxes that allowed free access to these species, they totally prevented the development of phorid flies and their parasitoids.