Aerial net primary productivity of a natural grassland of La Pampa province, Argentina

La productividad primaria neta aérea (PPNA) anual, estimada por un método decosecha, fue 561 , 508 y 161 g.m2 en 1982, 1983 y 1984, respectivamente. La misma mostró una distribución bimodal, en 1982 y 1983, con un pico primaveral y otro otoñal de menor magnitud; en 1984 hubo un solo máximo a fin de primavera. La biomasa verde mostró el mismo patrón que la PPNA. El material seco en pie se incrementó con el transcurso del tiempo, con un máximo durante la primavera y el verano de los dos últimosaños. La hojarasca no presentó una dinámica estacional regular, alcanzando la máxima acumulación durante el invierno de 1984. La biomasa total pasó de 517 g.m2 el primer año a 970 g.m2 el último. La relación biomasa seca/biomasa verde se incrementó durante el período de muestreo, siendo 1,3,2,5 y 4,5 para el primero, segundo y tercer año respectivamente. La reducción de la productividad primaria aérea en el tercer año podría deberse a: 1) las condiciones hídricas deficitarias reinantes y 2) a la gran acumulación de material seco en pie que interferiría la llegada de luz a las macollas.Aboveground net primary productivity (ANPP), estimated by a harvest method, was 561, 508 and 161 g.m2 in 1982, 1983 y 1984, respectively. Productivity showed a bimodal distribution in 1982 and 1983, with one peak in spring and a lower one in the fall. In 1984 there was only a peak at the end of spring. Green biomass showed the same pattern that ANPP. Standing dead showed an increasing trend, with a maximum during the spring and summer of the last two years. Litter did not show a seasonal dynamics, with the maximun peak in winter of 1984. Total biomass changed from 517 g.m22 (the 1st year) to 970 g.m2 (3rd year). The standing dead green biomass ratio increased during the sampling period: 1,3; 2,5 and 4,5 during the 1st, 2nd and 3rd year, respectively. The reduction of productivity during the 3rd year could be due to 1) low water availability conditions, or 2) that the standing dead material accumulated interfered the light to the tillers.Facultad de Ciencias Agrarias y Forestale

Feeding Habits and Trophic Niche Overlap of Aquatic Orthoptera Associated with Macrophytes

Fil: Capello, Soledad. Instituto Nacional de Limnología (INALI-CONICET-UNL). Santa Fé; ArgentinaFil: Marchese, Mercedes. Instituto Nacional de Limnología (INALI-CONICET-UNL). Santa Fé; ArgentinaFil: De Wysiecki, María Laura. Centro de Estudios en Parasitología y Vectores (CEPAVE). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

Aerial net primary productivity of a natural grassland of La Pampa province, Argentina

La productividad primaria neta aérea (PPNA) anual, estimada por un método decosecha, fue 561 , 508 y 161 g.m2 en 1982, 1983 y 1984, respectivamente. La misma mostró una distribución bimodal, en 1982 y 1983, con un pico primaveral y otro otoñal de menor magnitud; en 1984 hubo un solo máximo a fin de primavera. La biomasa verde mostró el mismo patrón que la PPNA. El material seco en pie se incrementó con el transcurso del tiempo, con un máximo durante la primavera y el verano de los dos últimosaños. La hojarasca no presentó una dinámica estacional regular, alcanzando la máxima acumulación durante el invierno de 1984. La biomasa total pasó de 517 g.m2 el primer año a 970 g.m2 el último. La relación biomasa seca/biomasa verde se incrementó durante el período de muestreo, siendo 1,3,2,5 y 4,5 para el primero, segundo y tercer año respectivamente. La reducción de la productividad primaria aérea en el tercer año podría deberse a: 1) las condiciones hídricas deficitarias reinantes y 2) a la gran acumulación de material seco en pie que interferiría la llegada de luz a las macollas.Aboveground net primary productivity (ANPP), estimated by a harvest method, was 561, 508 and 161 g.m2 in 1982, 1983 y 1984, respectively. Productivity showed a bimodal distribution in 1982 and 1983, with one peak in spring and a lower one in the fall. In 1984 there was only a peak at the end of spring. Green biomass showed the same pattern that ANPP. Standing dead showed an increasing trend, with a maximum during the spring and summer of the last two years. Litter did not show a seasonal dynamics, with the maximun peak in winter of 1984. Total biomass changed from 517 g.m22 (the 1st year) to 970 g.m2 (3rd year). The standing dead green biomass ratio increased during the sampling period: 1,3; 2,5 and 4,5 during the 1st, 2nd and 3rd year, respectively. The reduction of productivity during the 3rd year could be due to 1) low water availability conditions, or 2) that the standing dead material accumulated interfered the light to the tillers.Facultad de Ciencias Agrarias y Forestale

Grasshopper (Orthoptera: Acridoidea) species diversity in the Pampas, Argentina

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.Facultad de Ciencias Naturales y MuseoCentro de Estudios Parasitológicos y de Vectore

Diversidad y distribución de acridios (Orthoptera: Acridoidea) en pastizales del sur de la región pampeana, 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 distributio

Longevity and fecundity of Dichroplus maculipennis (Orthoptera, Acrididae) at non-outbreaking and outbreaking situations

Longevity and fecundity of Dichroplus maculipennis (Orthoptera, Acrididae) at non-outbreaking and outbreaking situations. Dichroplus maculipennis is one of the most characteristic and damaging grasshopper species of Argentina, mainly in areas of the Pampas and Patagonia regions. We estimated and compared the longevity and fecundity of adult female D. maculipennis under controlled conditions (30°C, 14L:10D, 40% RH) from individuals collected as last instar nymphs (VI) in the field and with a known recent history of low and high density conditions. Densities of D. maculipennis at the collecting sites were 0.95 individuals per m2 in 2006 and 46 ind/m2 in 2009, representing non-outbreaking and outbreaking situations, respectively. Adult female longevity in 2006 (67.96 ± 3.2 days) was significantly higher (p 0.05). The fecundity curves showed that the highest values were at weeks 11 and 13 for the 2006 females, and at week 6 for those of 2009. Since the daily oviposition rate at low and high densities was not significantly different, the diminished fecundity rate at high density is attributable to their reduced longevityLongevidade e fecundidade de Dichroplus maculipennis (Orthoptera: Acrididae: Melanoplinae) em situações de “nonoutbreaking” e “outbreaking”. O gafanhoto Dichroplus maculipennis é um dos mais característicos e prejudiciales da Argentina, principalmente nas regiões das Pampas e da Patagonia. O objetivo deste estudo foi estimar e comparar a longevidade e fecundidade das fêmeas adultas do D. maculipennis sob condições controladas (30°C, 14 luz: 10 obscuridad, 40% RH) a partir do indivíduos coletados em campo como ultimo estadio ninfal (VI) e con historia recente conocida de baixas e altas densidades. As densidades de D. maculipennis nos locais de coleta foram de 0.95 indivíduos por m2 em 2006 e 46 indivíduos/m2 em 2009, representando situações de “non-outbreaking” e “outbreaking”, respectivamente. A longevidade das fêmeas adultas em 2006 (67.96 ± 3.2 dias) foi significamente maior (p < 0.05) do que as de 2009 (37.44 ± 1.98 dias). O número de oviposiçãos por fêmea foi de 3.32 ± 0.44 para 2006 e 1.62 ± 0.26 para 2009. A fecundidade média em 2006 (89.29 ± 11.9 ovos/fêmea) foi significativamente maior (p < 0.05) do que a das fêmeas de 2009 (36.27 ± 5.82 ovos/fêmea). As curvas de fecundidade mostraram que os valores mais elevados ocorreram nas 11ª e 13ª semanas de 2006, e na 6ª semana para à quelas de 2009. Comparando a taxa diária de oviposição para altas e baixas densidades, não apresentaram diferenças significativas (p > 0.05). No entanto, as baixas taxas de fecundidade das fêmeas em densidades elevadas, se devem, provavelmente à longevidade reduzida.Centro de Estudios Parasitológicos y de VectoresFacultad de Ciencias Naturales y Muse

Grassland and shrubland grasshopper community composition in northern La Pampa province, Argentina

Fil: Wysiecki, María Laura de. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios en Parasitología y Vectores; ArgentinaFil: Sánchez, Norma Elba. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios en Parasitología y Vectores; ArgentinaFil: Ricci, Susana E.. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Humanas. Departamento de Sistemas Naturales y Ambiente; Argentin

Producción de raíces de dos pastizales pastoreados de la Sierra de la Ventana, Provincia de Buenos Aires, Argentina

La productividad radical de dos pastizales ubicados a diferente altitud fue estimada a partir del crecimiento de raíces dentro de cilindros de malla plástica rellenos con suelo libre de raíces. En el pastizal basal, ubicado a 450 m sm, la producción fue 560 g. m-2. año-1 y en el de altura, ubicado a 850 m sm, 565 g. m-2. año-1. El crecimiento fue netamente primaveral en el primero y primaveral y estival en el segundo. En ambos pastizales los procesos de desaparición de raíces dominaron en el verano y el otoño. La desaparición de raíces equivalió a 90% de lo producido anualmente en el pastizal basal y a 42 % en el de altura. La mayor concentración de biomasa de raíces (60-67%) se detectó en los primeros 10 cm de profundidad. Los picos de biomasa fueron 645 ± 85.8 g. m-2 en el pastizal basal y 477 ± 37.7 g. m-2 en el de altura, ambos en la primavera. La diferente fenología registrada en los procesos funcionales de estos pastizales puede explicarse por su diferente composición de especies, ya que en el basal predominaron gramíneas de ciclo inverno primaveral (micro y mesotérmicas), mientras que en el pastizal ubicado a mayor altura codominaron especies de ciclo estival (megatérmicas).Root productivity, estimated by growth into plastic (16 mm2 mesh) cylinders filled with soil free from roots, was 560 g. m-2 and 565 g. m-2 in a low altitude grassland (450 m sm) and a a high altitude grassland (850 m sm), respectively. Peaks of productivity were registered in spring in the low site and in spring and summer in the high site. Biomass losses dominated in summer and fall in both grasslands. 90% of annual production dissapeared at, the low grassland, and 42% at the high grassland. 60-67% of root biomass was concentrated in the top 10 cm of soil. Peaks of biomass were 645 ± 85.8 g. m-2 and 477 ± 37. 7 g. m-2 at the low and high altitude grasslands, respectively, and both were registered in the spring. The differences observed in these functional aspects of these grasslands might be attributed to their different species composition. The low-altitude grassland was dominated by cool-season grasses, while the high-altitude grassland was dominated by warm-season grasses

The biology and some population parameters of the grasshopper, Ronderosia bergi, under laboratory conditions

Some biological and population parameters of Ronderosia bergi (Stl) (Orthoptera: Acrididae: Melanoplinae) were estimated by monitoring five cohorts of the first generation (F1) of individuals born in captivity from grasshoppers collected in the South of Misiones province, northeastern Argentina, and held under controlled conditions (30° C, 14:10 L:D, 40% RH). The mean embryonic development time was 40.6 ± 1.7 days. Five nymphal instars were recorded. Total duration of nymphal development was 30.8 ± 0.54 days. The mean lifespan of cohorts was 22.6 ± 0.7 weeks. The number of egg-pods per female was 7.6 ± 1.44, and the amount of eggs per egg-pod was 16.45 ± 0.85. Mean fecundity was 125 ± 5.83 eggs per female with an oviposition rate of 1.55 ± 0.57 eggs/female/day. Survivorship curves showed that mortality was concentrated in the final weeks of adulthood, and the life expectancy curve decreased accordingly. The population parameters estimated gave the following values: the net rate of reproduction (R0) was 46.75 ± 11.2, generation time (T) was 18.87 ± 1.67 weeks, duplication time (D) was 3.31 ± 0.34, the intrinsic rate of population growth (rm) was 0.21 ± 0.021 and the finite rate of population increase () was 1.24 ± 0.026. The reproductive values (Vx) indicated that the largest contribution of females to the subsequent generation was between weeks 15 and 25.Centro de Estudios Parasitológicos y de Vectore