Early changes in Orthopteran assemblages after grassland restoration : a comparison of space-for-time substitution versus repeated-measures monitoring

Grasslands harbour significant biodiversity and their restoration is a common intervention in biodiversity conservation. However, we know very little on how grassland restoration influences arthropod groups. Here we compared orthopteran assemblages in croplands, natural grasslands and one to four-year-old grasslands restored in a large-scale restoration on former croplands in Hortobágy National Park (E-Hungary). Sampling was done by standardized sweep-netting both in a repeated measures design and space-for-time substitution (chronosequence) design. General linear models with repeated measures from five years showed that species richness, abundance and Shannon diversity of orthopterans decreased in the year following restoration but increased afterwards. By the fourth year, species richness almost doubled and abundance increased almost ten-fold in restored grasslands compared to croplands. Multivariate analyses showed that species composition in the first two years did not progress much but by the third and fourth year there was partial overlap with natural grasslands. Local restoration conditions (last crop, seed mixture) and landscape configuration (proportion of natural grasslands < 1 km away) did not influence the above patterns in either the repeated measures or the chronosequence design, whereas time since restoration affected almost all community variables. Our results suggest that generalist ubiquitous species appeared in restored grasslands first and the more sensitive species colonized the restored fields gradually in later years. The qualitative and quantitative properties of the orthopteran assemblages in restored fields did not yet reach those of natural grasslands, therefore, our study suggests that the full regeneration of the orthopteran assemblages takes more than four years

Decreased Functional Diversity and Biological Pest Control in Conventional Compared to Organic Crop Fields

Organic farming is one of the most successful agri-environmental schemes, as humans benefit from high quality food, farmers from higher prices for their products and it often successfully protects biodiversity. However there is little knowledge if organic farming also increases ecosystem services like pest control. We assessed 30 triticale fields (15 organic vs. 15 conventional) and recorded vascular plants, pollinators, aphids and their predators. Further, five conventional fields which were treated with insecticides were compared with 10 non-treated conventional fields. Organic fields had five times higher plant species richness and about twenty times higher pollinator species richness compared to conventional fields. Abundance of pollinators was even more than one-hundred times higher on organic fields. In contrast, the abundance of cereal aphids was five times lower in organic fields, while predator abundances were three times higher and predator-prey ratios twenty times higher in organic fields, indicating a significantly higher potential for biological pest control in organic fields. Insecticide treatment in conventional fields had only a short-term effect on aphid densities while later in the season aphid abundances were even higher and predator abundances lower in treated compared to untreated conventional fields. Our data indicate that insecticide treatment kept aphid predators at low abundances throughout the season, thereby significantly reducing top-down control of aphid populations. Plant and pollinator species richness as well as predator abundances and predator-prey ratios were higher at field edges compared to field centres, highlighting the importance of field edges for ecosystem services. In conclusion organic farming increases biodiversity, including important functional groups like plants, pollinators and predators which enhance natural pest control. Preventative insecticide application in conventional fields has only short-term effects on aphid densities but long-term negative effects on biological pest control. Therefore conventional farmers should restrict insecticide applications to situations where thresholds for pest densities are reached

Alpha and beta diversity of arthropods and plants in organically and conventionally managed wheat fields

1. Most studies in applied ecology use measures of alpha-diversity measures, i.e. the mean diversity on a site, to compare biodiversity effects of different management schemes. The total or alpha-diversity within a region, however, need not be correlated with the mean alpha-diversity within any site of the region. Thus, analyses of alpha-diversity alone may misrepresent the contributions of other diversity components (beta) to total diversity (gamma). 2. We apply a biodiversity-partitioning approach to species richness from a comparison between paired organic and conventional wheat fields in 21 sites from three regions in Germany, where we recorded plants, bees, carabids, staphylinids and spiders in the centre and edge of the fields. 3. Relative values of alpha- and beta-diversity depended on taxon. Both between-site and between-region beta-diversity were very high (in total 60-85%). alpha-Diversity and between-site beta-diversity was larger on the edge than in the centre of fields for all taxa. 4. alpha-Diversity, between-site beta-diversity of plants and bees and between-region beta-diversity of bees were higher in organic than in conventional fields, providing local as well as larger-scale species richness benefits. alpha-Diversity did not differ between management types for the epigaeic arthropods. Lower between-site beta-diversity was found for spiders in organic fields than in conventional fields, resulting in higher total species richness in conventionally managed wheat. 5. Similarity in composition of landscapes surrounding the study fields was correlated with similarity in species composition for epigaeic arthropods in conventional fields. For this group of organisms the variability of landscapes in the sample contributed to increasing beta-diversity. 6. Synthesis and applications. Diversity accounts for the major part of species richness in agro-ecosystems. Implementing an agri-environment scheme such as organic agriculture may result in either an additional increase of total diversity, as could be shown for plants and bees, or in a decrease in total diversity as was the case for the spiders. Therefore, beta-diversity needs to be included in the evaluation of different management schemes for conservation. For plant and bees it is recommended to implement agri-environment schemes in contrasting landscapes and in different regions to maximize total species richness benefits

Staphylinidae and Carabidae overwintering in wheat and sown wildflower areas of different age

Species richness and abundance of staphylinid and carabid beetles overwintering in winter wheat fields and 1- to 3-year-old wildflower areas were investigated during 2000/2001 on 16 study sites in Switzerland. Abundance and species richness of overwintering staphylinids significantly increased with successional age of the wildflower areas and were always higher in older wildflower areas than in winter wheat. A similar but less distinct pattern was observed for the abundance and species richness of carabid beetles. The influence of habitat parameters (vegetation cover, fine sand content, organic matter, pH, soil pore volume, surrounding landscape structure, habitat area) on the staphylinid and carabid assemblages based on the number of individuals per species and site was analysed using canonical correspondence analysis. Vegetation cover was the most significant parameter significantly characterizing both staphylinid and carabid assemblages. The amount of vegetation cover explained 15.7% of the variance, fine sand content accounted for 13.3% and surrounding landscape structure for 10.9% of the variance in the staphylinid assemblage. In the carabid assemblage, vegetation cover was the only significant factor, explaining 24.7% of the variance. This study showed for the first time that the significance of wildflower areas as a reservoir for hibernation for generalist predatory beetles increases with progressing successional age