Struktura troficzna ekosystemów trawiastych - studia porównawcze

Breymeyer, Alicja I.

doi:ISSN 0013-2969

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Title: Struktura troficzna ekosystemów trawiastych - studia porównawcze

Abstract:

This is a review and analysis of the latest ecological works on the trophic structure of grassland ecosystems. The analysis has been made as follows: (1) Introduction to the topic and definitions of basic terms used, (2) Autotrophs— vascular plants in grassland ecosystems, this including (2.1.) Production, (2.2.) P/B index, (2.3.) Vertical distribution of organic matter. The series of measurements of productivity of grassland ecosystems are compared (Table I) showing great similarity on the large areas of North America and Soviet Union. The difference between the highest and the lowest primary production is about ten-fold. The relationship between the above-ground plant production and the precipitation (Fig. 1) looks quite distinct. The prevalence of underground organic matter over the green one increases with the decreasing amount of water available in the environment (Figs. 2, 3, Table II). Grassland ecosystems have a very high P/B index which proves their high production efficiency as compared with other terrestrial ecosystems. (3). Heterotrophs — their ecological characteristics and role in matter cycling in the ecosystem. Distinct conditioning of trophic structure by ecosystem utilization, e.g., grazing, mowing is shown (Fig. 4). As a result of grazing in the grassland ecosystems a trophic chain of coprophagous forms is developed (Fig. 5). An analysis of the biomass distribution of various invertebrate consumers shows that the absolute prevalence is obtained usually by soil fauna, consisting mainly of saprophages (Table III). As regards bioenergetics characteristics, consumers of grassland ecosystems show a great variety (Fig. 6, analyses of indices A/C, P/A, R/A, in the paper). But always the expenditure of energy on living costs distinctly exceeds that on production of body tissues. (4) Trophic pyramids in grassland ecosystems and (5) Quantitative relations among trophic levels. On the basis of American (Fig. 7) and French literature (Fig. 8) trophic pyramids of different grassland ecosystem types are discussed and then the quantitative relations among trophic levels are calculated (Tables IV—VI). It has been found that even several thousands (2000—3000) units of heterotrophe biomass fall per a unit of autotrophe biomass — as it happens in ecosystems under bad, extreme abiotic conditions. Whereas it is 70—300 in ecosystems of temperate zones. The biomass ratio for levels of consecutive consumers (phytophages/predators) ranges from 2 to 18 and thus is several rows lower. The last chapter „Remarks on the strategy of grassland ecosystems” is a discussion of various possible ways of evolution of grassland ecosystems.