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Receptividad ganadera: marco teórico y aplicaciones prácticas
Golluscio,Rodolfo;
Ecolog?-a austral , 2009,
Abstract: this article is conceived as a didactic aid to use in graduate and post-graduate courses of ecology and grassland science. it aims to illustrate the concept of carrying capacity when applied to animal production systems, and also the difficulties involved in its calculus. the concept of carrying capacity derives from the classical logistic model of population growth, and is defined as the maximum density a population can attain in one habitat. however, that model assumes that (1) the environment is invariable in time and space, (2) all the individuals of the depredators or parasites. taking into account that these three assumptions are not fulfilled in animal production systems, and that human intervention alters ecosystem carrying capacity, the concept of carrying capacity of animal production systems differs from that of the logistic model. the carrying capacity of animal production systems has been defined as "the maximum animal density that can be maintained in one area under a certain production level without deteriorate the resource". the most adequate conceptual framework to understand the factors determining the carrying capacity of animal production systems is the model of energy flux. it suggests that domestic herbivores may consume only a proportion of aboveground net primary production, known as harvest index, to make a sustainable use of rangeland ecosystems. there not exist, until now, an universally accepted methodology to estimate the carrying capacity of animal production systems because of: (1) the lack of reliable models to predict harvest index in sites differing in environmental conditions or vegetation structure, or in different years or seasons, (2) the vast array of factors determining carrying capacity, including those directly linked to forage availability (as precipitation, fertility, soil texture, etc.) as good as those environmental factors unlinked to forage availability (as water availability, climatic risks, predators, etc.) and those
Arbustos de la estepa patagónica: ?adaptados a tolerar la sequía o el pastoreo?
Golluscio,Rodolfo A; Cavagnaro,Fernando P; Valenta,Magalí D;
Ecolog?-a austral , 2011,
Abstract: drought is the main selective force in arid zones acting on plant populations. features that confer plants tolerance to drought also provide tolerance to herbivory. therefore, even the plants of arid zones with a short grazing history would be tolerant to herbivory. evolutionary history of grazing in central and northwest patagonian steppes has been considered brief and dominant spiny shrubs have been considered adapted to tolerate drought. here, we present experimental evidences that question that conceptual model. (1) the three most conspicuous shrubs in the dominant community at south-western chubut (mulinum spinosum, adesmia volckmanni and senecio filaginoides) are not subjected to severe water stress conditions because their roots explore deep soil layers with relatively high water potentials almost all year. that is reflected in high leaf water potential, high isotopic discrimination against heavy carbon isotope and low response to rainfall. (2) instead, the three shrubs show evasion herbivory strategies. m. spinosum and a. volckmanni have very aggressive thorns, while s. filaginoides has a high content of carbon-based secondary metabolites. these chemical compounds are believed to have an anti-herbivory role. besides that, in two of these three species, levels of physical or chemical defences were increased under grazing conditions. (3) finally, as defensive strategies do not preclude herbivore consumption in absolute terms, shrubs are important components of sheep diet. sheeps eat leaves of non-chemically defended species and flowers of all of them. these evidences suggest that grazing pressure of native herbivores would have been high and persistent enough to promote natural selection processes that conducted to dominance of grazing resistant shrub genotypes.
Cálculo de la receptividad ganadera a escala de potrero en pastizales de la Pampa Deprimida
Vecchio,María Cristina; Golluscio,Rodolfo A; Cordero,Miriam I;
Ecolog?-a austral , 2008,
Abstract: we estimated the carrying capacity (cc) of a farm by combining satellite images, aimed at measuring the area of each plant community, with biomass measurements to estimate aboveground net primary production (anpp) and the proportion of anpp that can be consumed by animals (harvest index; hi). we estimated cc of each paddock as the mean cc of the different plant communities, weighed by the area occupied by each community within the paddock. carrying capacity of each community was obtained as the ratio between the product of anpp x hi and the individual annual intake. we estimated the anpp of the most conspicuous plant communities (b and i) within an area that had been fenced to exclude domestic herbivores two years before the beginning of this study. we estimated hi as the ratio between consumption and anpp, estimating animal intake from the biomass loss between entry and exit of animals from grazed paddocks. community b showed a higher anpp and hi than community i (4584 vs. 2969 kg dm.ha-1.yr-1 and 75% vs. 61%, respectively). the carrying capacity of each paddock ranged between 0.6 and 0.8 animal units.ha-1.yr-1, was associated to the proportion of the area occupied by community b, and was higher than the cc estimated from empirical models. our results suggest that both quality and reliability of cc estimates depend on quality and reliability of available anpp and hi data.
Mapeo indirecto de la vegetación de Sierra de la Ventana, provincia de Buenos Aires
Lizzi,José M; Garbulsky,Martín F; Golluscio,Rodolfo A; Deregibus,Alejandro V;
Ecolog?-a austral , 2007,
Abstract: the cartography of the vegetation increases the understanding of the extension and spatial distribution of different communities and has become an important tool for planning strategies for both conservation and use. remnant grasslands in buenos aires province have been well-studied, though the vegetation of sierra de la ventana has yet to be mapped at a level of detail appropriate to its spatial heterogeneity. one reason for this, is that conventional photo interpretation or image classification techniques are less suitable for making good vegetation maps of areas with complex topography. in this study we used techniques of predictive vegetation mapping at a regional scale and applied it to the natural vegetation of sierra de la ventana, a hill system located in southwestern buenos aires with a large part devoted to agriculture and livestock grazing. the technique presented in this paper combines remote sensed data (landsat tm7) and a digital elevation model at a regional scale, with a previous study that related the most conspicuous plant communities in the region with topography at a more detailed scale. we constructed an algorithm to assign each pixel to the corresponding vegetation unit (vu) that uses the geo-edaphic environment and topographic variables as input variables. the sixteen vu identified using the digital data (spatial resolution = 90 m) showed a high correlation with the vu identified in the field (r = 0.88, n = 100 ground control points). the technique developed in this study represents an advance on vegetation mapping and could be extrapolated to other hilly areas that already have a basic vegetation description. our results provide new knowledge on the spatial heterogeneity of this area. the map of natural vegetation is a useful resource for improving grazing management. some of the differences between field data from the foothill sites and the derived map may arise from the impacts of grazing. our results could help to generate hypotheses on th
Caracterización química de arbustos patagónicos con diferente preferencia por parte de los herbívoros
Cavagnaro,Fernando P; Golluscio,Rodolfo A; Wassner,Diego F; Ravetta,Damián A;
Ecolog?-a austral , 2003,
Abstract: in southwestern chubut (patagonia, argentina), shrubs provide safe sites for the recruitment of almost all the species of the community. as different shrubs species are subjected to different sheep grazing pressures, the knowledge of their response mechanisms to grazing is crucial to the designing of sustainable systems of grazing management for these ecosystems. this work tested two hypotheses related to the adaptive and plastic responses to grazing for the three dominant shrubs of this community (adesmia campestris, mulinum spinosum and senecio filaginoides). we studied the chemical composition of leaves of these shrubs under two contrasting sheep grazing pressures. we carried out a chemical screening to sequentially extract three groups of different polarity carbon based secondary metabolites (cbsm): oil, phenols and hydrocarbon compounds. we found that (1) the less preferred species (senecio filaginoides) contained higher levels of the three fractions of cbsm than the other two species (adaptive response), and (2) only in senecio filaginoides the cbsm content, in particular those of oil and hydrocarbon fractions, increased with grazing. the absence of plastic responses in the other two species could be related to the presence of structural defenses (thorns).
Divergencias en la estimación de receptividad ganadera en el noroeste de la Patagonia: diferencias conceptuales y consecuencias prácticas
Golluscio,Rodolfo A; Bottaro,Hugo; Rodano,Daniel; Garbulsky,Martín F; Bobadilla,Segundo; Buratovich,Osvaldo; Villa,Martín;
Ecolog?-a austral , 2009,
Abstract: an effective estimate of the carrying capacity of different vegetation types would contribute to reduce some grazing-induced desertification processes in patagonia. at present there are several methods in use. however, none can be considered "a priori" as the reference-method. in this study, we compared the estimates obtained by two commonly used in northwestern patagonia, aboveground net primary productivity method (mppna) and pastoral value method (mvp). using both methods, we calculated the carrying capacity for 119 sites encompassing a wide range of anpp (130 to 2100 kg dm.ha-1.y-1). estimates obtained using mppna were generally higher than those obtained using mvp, and the difference widened as anpp increased. we used path analysis to identify the determinants of both estimates and their difference. mppna values depend mainly on anpp, as the other component of the metric (harvest index) is also calculated as a function of anpp. on the other hand, mvp values are more strongly dependent on the value of forage consumed prior to measurement than on the pastoral value of the stand at that time (vpstand), as the latter is used to estimate the amount of forage available at the time of measurement. vpstand, in turn, depends more on forage cover than on the vp of the vegetation (vpveg). as expected, the difference between the two carrying capacity estimates widened as anpp increased and as forage consumed prior to measurement decreased. the difference between estimates also broadened as vpstand increased, reflecting an indirect effect of anpp as sites of high vpstand had also high anpp and forage cover. the analysis suggests that mppna and mvp provide the upper and lower limits, respectively, to carrying capacity estimates. these estimates could be improved by developing more reliable models for the estimation of harvest index and forage available at the time of measurement, reducing the sensitivity to anpp of the first variable and increasing the sensitivity to anpp of
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