Aim The objectives of this study were to relate species density, richness and relative abundance of grasshoppers to habitat vegetation and to detect variations in these variables among native and exotic plant communities which reflected disturbance history.Location Twenty-seven sites were selected in 2000 representing a variety of native and exotic plant communities, with different degrees of disturbance history, in south-east Buenos Aires province, Argentina.Methods Grasshopper mean density, species relative abundance and species composition were estimated at each site via standard flushing and sweep net techniques. Plant associations at each site were estimated by evaluating the percentage canopy of ground cover of native perennial grasses, introduced perennial forbs, annual pastures, halophilous species, perennial pastures, native perennial forbs, introduced annual forbs and plant species richness. Based on vegetation variables, sites were classified into five disturbance categories: native grasslands, halophilous grasslands, pastures, moderately disturbed pastures and highly disturbed pastures. ResultsGrasshopper communities from sites dominated by introduced plant species (forbs, sown grasses and dicots), were characterized by relatively high densities and a high proportion of potential pest species. Native grassland sites showed lower grasshopper densities, while halophilous grassland had high densities, but with low proportion of potential pest species.Main conclusions Results from this study suggest that the most abundant and economic important species of the pampas, Dichroplus elongatus, was associated with sown pasture plants (grasses and dicots) and introduced forbs, and negatively correlated with natural communities (native vegetation and halophilous species). These relationships imply that appropriate management practices that leave more areas with natural vegetation and include perennial pastures and native species in the rotations could show beneficial in reducing the overall density and the proportion of the primary pest species in south-eastern Buenos Aires province.
Abstract. A study was conducted to describe the major features of geographical and temporal variation in the diversity of grassland grasshopper species (Orthoptera: Acridoidea) in different sites of the Pampas, Argentina. Species richness and relative abundance were assessed at 12 sites in eastern La Pampa and western Buenos Aires provinces, from 1994 through 1999. Mean species richness at the regional level was 10, and 34 grasshopper species were collected throughout of the study. Comparison with grasshopper species diversity from the Great Plains of North America is discussed. An evaluation of the proportions of species in each of the three distribution groups (broad, intermediate and narrow) revealed that, over all sites, broadly distributed species made up 14.7% of species composition and intermediately and narrowly distributed species made up 26.5% and 58.8%, respectively. The three top‐ranked species in the studied sites were Dichroplus elongatus, D. pratensis and Staurorhectus longicornis. Results showed that, contrary to what was expected, one of the widely distributed species in the region (i.e. Baeacris punctulatus) does not always constitute one of the most abundant species. Finally, the loss of one of the historically most common species in the Pampas, D. maculipennis, is also discussed.
Diversity and distribution of grasshoppers (Orthoptera: Acridoidea) in grasslands of the Southern Pampas region, Argentina. In Argentina, the grasslands of Pampas region comprise approximately 15% of the country. As in other grasslands of the world, grasshoppers are among the most important native herbivores. Their economic importance has been recognized in Argentina since the mid to late nineteenth century, since outbreaks of different species have become recurrent phenomena. Therefore, the main objective of this work was to study their diversity and distribution in grasslands of the Southern Pampas region (Laprida county, Buenos Aires province), as one of the most affected areas. The study was conducted during five seasons (2005-10). Sampling sites were represented by the most common plant communities in this area, classified in four categories: native grasslands, disturbed grasslands, implanted pastures and halophilous grasslands. The samplings were conducted from mid-spring to early autumn, with five or six samples per season. We estimated the following population descriptors: species richness (S), eveness (E), dominance (J), and diversity index (H´). In order to evaluate the similitude of the grasshopper communities present in the different plant communities, we used qualitative and quantitative coefficients of similitude. A total of 22 species of grasshoppers were collected, of which 21 belong to the family Acrididae. The subfamily Melanoplinae was the most diverse with eight species. The largest species richness was recorded in native grasslands (18). The different communities of grasshoppers had similar indices of evenness and dominance (p>0.05). Considering all plant communities, the average value of Shannon-Wiener index was 1.58±0.075. There was a positive correlation between evenness index and species richness (p<0.05). The diversity index H' was different between plants communities (p<0.05), and it was higher in the disturbed grassland (1.75±0.096, p<0.05) than in the halophilous grasslands (1.34±0.12). Native and disturbed grasslands had a higher plant richness than halophilous grasslands and implanted pastures (p<0.05). There was a positive relationship between plant richness and grasshoppers species richness, and diversity of grasshoppers. According to the qualitative indices applied, the similitude between different grasshopper communities was higher than 60%. In general, the species that had a higher frequency of occurrence showed greater abundance and distribution. Covasacris pallidinota, Dichroplus elongatus, D. maculipennis, Borellia bruneri and B. pallida were the most widely distributed species, most of them (12) showed a restricted distribution and few (five) an intermediate distribution.
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