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The STUDIA UNIVERSITATIS BABEÅž-BOLYAI issue article summary
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Abstract: In the natural ecosystems from the superior sector of the Arie¿ River basin (spruce forests, mixed forests, beech forests, coppices and meadows) there are 8 species of terrestrial isopods: Ligidium hypnorum, Hyloniscus riparius, Hyloniscus transsylvanicus, Protracheoniscus politus, Megepimerio vareae, Trachelipus wächtleri, Porcellium conspersum and Armadillidium carniolense. The specific structure of the isopod communities differs in relation to the type of ecosystem, and also between ecosystems of the same type. We can not conclude that a certain isopod community is typical for a certain ecosystem from low mountain areas. In the researched mountain meadows there live sylvan, humicolous and paludicolous isopod species. The individuals of the populations have a dispersion that is limited to the microhabitats with high humidity and moderate temperatures. Here there are no praticolous species, which are typical for the meadows occurring on hilly and plane areas. Probably, the average annual temperatures recorded in mountain meadows are situated outside of the limits of the optimum thermal values for praticolous species. In forests, the sylvan species Protracheoniscus politus and Trachelipus wächtleri have a wide dispersion on the surface of the soil underneath the litter layer, due to the broad limits of their ecological valence. They tolerate wide oscillations of the temperature and humidity. Paludicolous species (Ligidium hypnorum, Hyloniscus transsylvanicus, H. riparius), humicolous species (Porcellium conspersum) and two sylvan species (Megepimerio vareae and Armadillidium carniolense) have a very low tolerance to the variations of temperature and humidity. Their dispersion in a biotope is limited to microhabitats with high and constant humidity and moderate temperatures that can not exceed 15-18ºC. The dispersion pattern influences the values of the frequency of the species, and also their numerical and relative abundance. The species that depend on a certain type of microhabitat have, in general, small populations in an ecosystem and a low frequency in the collected samples. However, these are not considered to be accidental species, as long as their favorite microhabitats are permanent in an ecosystem. They belong to the category of accessory species. The populations of Protracheoniscus politus have a frequency of 70-100% in all the studied ecosystems. It is a constant and euconstant species, both in forest ecosystems and in meadows. In the forest ecosystems, it is a dominant species. In the studied ecosystems in which the values of ecological diversity and evenness are relatively high, for instance in certain spruce and beech forests, the isopod populations are numerically reduced for all species. The ecological conditions are at the limit of their biological optimum and, in consequence, the survival coefficient is low for the entire community of species. |
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