ANALYSIS OF SPECIES COMPOSITION AND ABUNDANCE OF GRASSHOPPERS (ORTH, ACRIDIDAE) IN NATURAL AND FERTILIZED GRASSLANDS

Grasshopper densities were estimated in natural and agricultural grasslands on sandy soils. As compared to other arthropod groups grasshoppers react strongly to increasing fertilization level, first by decreasing species number next by decreasing density. This makes the combination of grasshopper species number and density to a sensitive tool for the monitoring of nitrogen load in grasslands. Effects of management type were insignificant. High percentages of grasshopper variation explained by maximum temperature, vegetation biomass, light extinction and intensity of the management suggest that these factors affect grasshoppers more than the fertilizer load does. This is supported by several field observations from literature. It is hypothesized that the distributions of grasshopper species with relatively slow development rates are shrinking by the effects of enhanced eutrophication on grasshopper environment, viz. increasing height and structural density of the vegetation, and consequently decreasing maximum temperature near the soil surface; slowly developing species may not be able to complete their annual cycle in such a cool environment. The positions of species on gradients are interpreted and discussed.