Plant and insect diversity along a pollution gradient: understanding species richness across trophic levels

We analysed species richness of plants and true bugs (Insecta, Heteroptera) along a pollution gradient in Scots pine stands in Central Germany. As a c onsequence of particulate deposition, pH-values of soils increased in the v icinity of the emission source. Therefore, emission increased productivity. Species richness of plants increased with decreasing distance from emissio n source, and thus with increasing productivity. Similarly, species richnes s of herbivorous Heteroptera increased with decreasing distance from emissi on source, whereas, surprisingly, abundance decreased. The proportion of sp ecialised herbivorous bug species is largest in the vicinity of the emissio n source. Thus, the diversity pattern of herbivores may be explained by the 'specialisation hypothesis' and not the 'consumer rarity hypothesis'. Spec ies richness and abundance of carnivorous Heteroptera showed no significant trend along the gradient. Overall our data favour the 'bottom-up' control of species diversity in the analysed system.