Abstract:

En las zonas áridas de Argentina, los bosques de <i>Prosopis flexuosa</i> son de suma importancia porque protegen el suelo en áreas con riesgo elevado de desertificación, y porque ofrecen diversos recursos a los pobladores locales (e.g., leña, forraje y productos alimenticios derivados de sus frutos). La actividad antrópica ha tenido un fuerte impacto sobre estos bosques, en especial desde la segunda mitad del siglo XIX. Por lo tanto, conocer su distribución potencial y compararla la distribución actual permitirá definir zonas prioritarias para la conservación y proponer posibles áreas de reforestación. El objetivo de esta investigación fue generar un modelo de distribución potencial de los bosques de <i>P. flexuosa</i> en la Provincia Biogeográfica del Monte. Para obtener el mapa modelo se utilizó el software Maxent, tomando como datos los registros georeferenciados de presencia de bosques de <i>P. flexuosa</i> y de variables ambientales relevantes para la distribución de muchas especies (variables climáticas, subórdenes de suelos y profundidad de napa freática). En general, el mapa de distribución potencial resultante concuerda con la ubicación de los principales valles, bolsones y llanuras del Monte, en donde se conoce la existencia actual de los bosques de <i>P. flexuosa</i>. Sin embargo, las superficies y los límites de los bosques estimados y los observados difieren en algunos casos, lo que se relacionaría con disturbios antrópicos y/o con otras variables no consideradas en el modelo, como la probabilidad de incendios.

In arid areas of Argentina, <i>Prosopis flexuosa</i> woodlands are of foremost importance since they are thought to protect the soil against erosion in a region with a high risk of desertification, and because they offer several resources to local inhabitants, such as firewood, forage for cattle, and food products derived from its fruit. These woodlands have been strongly impacted by human activities, mainly during the first half of the XIXth century. Knowledge about their potential distribution, as well as a comparison between potential and actual distributions, would allow priority areas for conservation and possible areas for reforestation to be defined. The aim of this work was to generate a model of the potential distribution of <i>P. flexuosa</i> woodland within a region of arid shrublands in central Argentina, known as the Monte desert. Maxent software was used to generate the distribution models. The sofware uses as input a set of georeferenced data of the presence of <i>P. flexuosa</i> woodland, and of those relevant for the distribution of species (e.g., climatic, altitude, slope, aspect, soil and water table depth). The resulting potential distribution model generally coincided with the main valleys, depressions and plains of the region, where <i>P. flexuosa</i> woodland are known to exist currently. However, area and limits of observed and estimated woodland patches differ in some cases, which could be related with anthropogenic disturbances in some of the patches or with variables not included in the model, such as the probability of wildfires.

Abstract:

La introducción de ganado doméstico provocó modificaciones en la vegetación y en el suelo de la Patagonia extra-andina. Estos cambios alteraron procesos ecosistémicos, aumentaron la desertificación y causaron pérdida de biodiversidad. Es frecuente encontrar gradientes decrecientes de actividad animal partiendo de las aguadas (piósferas), que resultan adecuados para determinar el impacto del pastoreo sobre los ecosistemas. El objetivo de este estudio fue evaluar el efecto de la intensidad de pastoreo ovino a partir de gradientes de piósfera sobre la estructura de la vegetación y el suelo en estepas arbustivas representativas de Península Valdés, Argentina. Mediante modelos lineales generalizados mixtos (GLMM) y técnicas multivariadas se estudiaron las variaciones en la cobertura vegetal, complejidad vertical de la vegetación, número y área de parches vegetados, microtopografía del suelo y su compactación en relación con el gradiente de pastoreo. La intensidad del pastoreo disminuyó con la distancia a la aguada y explicó más de 50% de la variabilidad ambiental. Esto demuestra la existencia de efecto piósfera. La cobertura de herbáceas, mantillo, complejidad vertical de la vegetación y la microtopografía aumentaron al disminuir la presión de pastoreo en los sitios más alejados de la aguada, mientras que el porcentaje de suelo desnudo, gravas, cobertura de anuales y la compactación del suelo presentaron un patrón opuesto. Este estudio evidencia, por primera vez, la existencia de piósferas ovinas en Península Valdés e indica que la intensidad de pastoreo en la región se asocia con alteraciones ambientales compatibles con procesos importantes de degradación ecosistémica. Dada la importancia que reviste la península en el contexto de la conservación biológica de la región, se requieren más estudios de este tipo para una implementación efectiva de medidas de manejo que integren la ganadería y la conservación de los recursos naturales.

The introduction of domestic livestock in the arid Patagonia produced changes in vegetation and soil that altered fundamental ecosystem processes, increasing desertification and biodiversity loss. In this region, it is common to observe gradients of decreasing animal activity from watering points where livestock impact is greatest near the watering sites, called piospheres, particularly suitable for assessing the effect of grazing on arid ecosystems. The aim of this study was to evaluate the effect of sheep-grazing intensity using piospheres on the structure of the vegetation and soil in shrubby steppes of Peninsula Valdes, Argentina. Variation of plant cover, vertical complexity of the vegetation, number and area of vegetated patches, micro-topography and soil compaction in relation to piosphere gradients were studied using Generalized Linear Mixed Models (GLMM) and multivariate analyses. Grazing intensity decreased according to increasing distance to the watering point. This fact, explaining more than 50% of the overall environmental variability, confirmed the existence of a piosphere gradient on each studied site. Such environmental changes were characterized by a gradual increase in grass and litter cover, vertical complexity of vegetation and soil microtopography at increasing distances from the watering point. Percentages of bare soil and gravel, cover of annual grasses and soil compaction showed the opposite pattern. This study demonstrates, for the first time, the existence of sheep piospheres in the shrubby steppes of Peninsula Valdes. Our results indicate that sheep-grazing intensity is associated with changes in the structure and composition of the vegetation and the soil characteristics that are compatible with degradation processes in the study region. Taking into account the importance of Peninsula Valdes in the context of biodiversity conservation, more studies of this type are required to implement effective management actions integrating livestock and conservation efforts on the terrestrial ecosystems of the region.

Abstract:

In arid conditions, the low quality of the forage and water shortage could be attenuated by the introduction of Opuntia species. Several plant species grows well under Prosopis canopy, responding to a higher nutrient content in the soil, It was hypothesized that productivity and nutrient content, mainly crude protein (CP), of Opuntia ellisiana planted under Prosopis would be higher than of those planted outside the canopy, and that these parameters would be influenced by the cactus position: north or south from the centre of the tree. Sampling was done in 18 plants under the canopy of Prosopis and 23 outside of it. After one year of the plantation, the totality of cladodes was harvested. The productivity per plant was 3.1 and 5.7 cladodes and 34.9 and 48.1 g of dry matter (DM), outside and under the canopy, respectively. The bromatological values (%) were moisture: 89.1 and 91.9, organic matter (OM): 76.7 and 79.8, CP: 4.4 and 8.1, acid detergent fiber (ADF): 13.7 and 18.2, neutral detergent fiber (NDF): 29.0 and 31.5, K: 3.1 and 3.6, P: 0.07 and 0.11, Ca: 5.5 and 4.4, Na: 0.04 and 0.02, outside and under the canopy, respectively. Crude protein, moisture, OM, ADF, NDF, K, P and productivity per plant were higher under the canopy, whereas Ca and Na values were higher outside the canopy (p&lt;0.05). Magnesium (1.9 and 1.9%) was not affected by the position outside or under the canopy. The north or south orientation did not influence any of the analysed parameters.

En condiciones de aridez, la baja calidad del forraje y la escasez de agua podrían ser atenuadas con la introducción de especies de Opuntia. Varias especies tienen buen crecimiento bajo la canopia de Prosopis spp., respondiendo a un contenido más alto de nutrientes en el suelo. Se hipotetizó que la productividad y el contenido de nutrientes, principalmente proteína cruda (PC), de Opuntia ellisiana establecidas bajo la canopia de Prosopis serían más altos que los implantados fuera de la misma y que estos parámetros serían influenciados por la posición del cactus: norte o sur respecto del centro del árbol. Se muestrearon 18 plantas de cactus bajo la canopia y otras fuera de la misma. Después de un año de crecimiento, se cosechó la totalidad de los cladodios. La productividad por planta fue 3,1 y 5,7 cladodios y 34,9 y 48,1 g de materia seca (MS), fuera y bajo la canopia, respectivamente. Los valores bromatológicos (%) fueron humedad: 89,1 y 91,9, materia orgánica (MO): 76,7 y 79,8, PC: 4,4 y 8,1, fibra detergente ácida (FDA): 13,7 y 18,2, fibra detergente neutra (FDN): 29,0 y 31,5, K: 3,1 y 3,6, P: 0,07 y 0,11, Ca: 5,5 y 4,4, Na: 0,04 y 0,02, bajo y fuera de la canopia, respectivamente. Proteína cruda, humedad, MO, FDA, FDN, K, P y productividad por planta fueron más altas bajo la canopia, mientras que los valores de Ca y Na fueron más altos fuera de la canopia (p&lt;0.05). Magnesio (1,9 y 1,9%) no fue afectado por la posición bajo y fuera de la canopia, respectivamente. La orientación norte o sur no influenció los parámetros analizados.

Author affiliation: Grünwaldt, Josefina María. Instituto Argentino de Investigaciones de las Zonas Áridas <IADIZA>

Author affiliation: Guevara, Juan Carlos. Instituto Argentino de Investigaciones de las Zonas Áridas <IADIZA>

Author affiliation: Martínez Carretero, Eduardo. Instituto Argentino de Investigaciones de las Zonas Áridas <IADIZA>

Author affiliation: Grünwaldt, Eduardo Guillermo. Instituto Argentino de Investigaciones de las Zonas Áridas <IADIZA>

Abstract:

Interactions mediated by extrafloral nectary (EFN)-bearing plants that reward ants with a sweet liquid secretion are well documented in temperate and tropical habitats. However, their distribution and abundance in deserts are poorly known. In this study, we test the predictions that biotic interactions between EFN plants and ants are abundant and common also in arid communities and that EFNs are only functional when new vegetative and reproductive structures are developing. In a seasonal desert of northwestern Argentina, we surveyed the richness and phenology of EFN plants and their associated ants and examined the patterns in ant–plant interaction networks. We found that 25 ant species and 11 EFN-bearing plant species were linked together through 96 pairs of associations. Plants bearing EFNs were abundant, representing ca. 19 % of the species encountered in transects and 24 % of the plant cover. Most ant species sampled (ca. 77 %) fed on EF nectar. Interactions showed a marked seasonal pattern: EFN secretion was directly related to plant phenology and correlated with the time of highest ant ground activity. Our results reveal that EFN-mediated interactions are ecologically relevant components of deserts, and that EFN-bearing plants are crucial for the survival of desert ant communities.

Author affiliation: Aranda Rickert, Adriana Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Cientificas y Transferencia Tecnológica de Anillaco; Argentina

Author affiliation: Diez, Patricia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Cientificas y Transferencia Tecnológica de Anillaco; Argentina

Author affiliation: Marazzi, Brigitte. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina

Abstract:

The discovery of biotic and ecological factors that influence genetic isolation in populations contributes to our understanding of speciation, one of the most important issues in evolutionary biology. In this paper, we ask whether differences in climate preferences are influencing genetic isolation in two assemblages of populations of Berberis trifoliolata Moric., the Northeastern and the Mexican Plateau groups. Agarito, as this species is known, is a remarkable shrub in the arid regions of North America and found mostly in the Chihuahuan Desert. Ecological niche modeling and two tests of niche evolution were carried out. The Ecological Niche Modeling suggests that the potential distribution of the Northeastern group does not predict that of the Mexican Plateau group, and nor does the latter predict the former. Tests of niche evolution indicate a divergent niche between these two groups. Among the most important climate factors detected in the multivariate niche evolution test are mean annual temperature and annual precipitation. We concluded that the two lineages exemplify an incipient speciation process.

Author affiliation: Angulo, D. F.. Instituto de Ecologia; México

Author affiliation: Amarilla, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina

Author affiliation: Sosa, V.. Instituto de Ecologia; México

Abstract:

A large number of protected areas worldwide have been impacted by biological invasions, threatening the biodiversity they aim to protect. The wild boar (Sus scrofa) is one of the most threatening invasive species in Argentina, already occupying many ecoregions, including the central Monte Desert. However, there are no studies regarding the use that wild boars make of this invaded biome and what factors (climate or landscape) determine or contribute to the establishment of this species. The objectives of this study were to assess habitat use of the wild boar at spatial and temporal scales in the central Monte Desert, and to assess if climatic factors influence its abundance. Our results show that, at habitat-level the wild boar exhibited preferences for a particular habitat (Larrea shrubland) for feeding. At microhabitat-level, we found a positive association between herb cover and wild boar presence. In addition, we found a strong and positive association between the number of days with low temperatures and the number of wild boar signs registered. Therefore, we consider that in the central Monte Desert, habitat selection by wild boars is most likely determined by a maximization of food intake and a minimization of exposure to high temperature.

Author affiliation: Cuevas, Maria Fernanda. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Mendoza. Instituto Arg de Invest. de Las Zonas Aridas; Argentina;

Author affiliation: Ojeda, Ricardo Alberto. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Mendoza. Instituto Arg de Invest. de Las Zonas Aridas; Argentina;

Author affiliation: JAKSIC ANDRADE, Fabián Miguel. Universidad Catolica de Chile. Center For Advanced Studies In Ecology And Biodiversity; Chile;

Abstract:

Biotic interactions are vital to ecosystem functioning. Interactions among individuals lie at the core of population and community dynamics, and therefore play a central role in the existence and persistence of species. Plants form the food base of most terrestrial ecosystems and are therefore not surprisingly involved in a substantial portion of biotic interactions. Plants, animals, and microbes face great challenges to survival in the desert environment, and these interactions play a critical role in the survival of many species.

Author affiliation: Marazzi, Brigitte. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina

Author affiliation: Bronstein, Judith L..

Author affiliation: Sommers, Pacifica N..

Author affiliation: López, Blanca R..

Author affiliation: Bustamante Ortega, Enriquena.

Author affiliation: Búrquez, Alberto.

Author affiliation: Medellín, Rodrigo A..

Author affiliation: Aslan, Clare.

Author affiliation: Franklin, Kim.

Abstract:

Assemblage patterns could be primarily generated by two types of drivers: exogenous (such as environmental and climatic factors) and endogenous (interactions such as competition, predation, mutualism or herbivory). The most widely accepted hypothesis states that at smaller scales (such as patch scale),interspecific interactions are the major drivers structuring communities, whereas at larger regional scales, factors such as climate, topography and soil act as ecologicalfilters that determine assemblage composition. The general aim of this paper is to compare different exogenous drivers in terms of theirrelative dominance in structuring desert small mammal communities across a range of spatial scales, from patch to regional, and compare them with previous results on endogenous drivers. Our results show that as spatial scale increases, the explanatory power of exogenous factors also increases, e.g. from 17% atthe patch scale (i.e. abundance) to 99% at the regional scale (i.e. diversity). Moreover, environmental drivers vary in type and strength depending on the community estimator across several spatial scales. On the other hand, endogenous drivers such as interspecific interactions are more important at the patchscale, diminishing in importance towards the regional scale. Therefore, the relative importance of exogenous versus endogenous drivers affects small mammal assemblage structure at different spatial scales. Our resultsfill up a knowledge gap concerning ecological drivers of assemblage structure at intermediate spatial scales for Monte desert small mammals, and highlight the importance of dealing with multi-causal factors in explaining ecological patterns of assemblages.

Author affiliation: Rodriguez, Maria Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina

Author affiliation: Ojeda, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina

Abstract:

The wild boar, Sus scrofa, was first introduced for hunting purposes in Argentina in 1906 and presently occupies a wide range of habitats. Understanding the food habits of invasive species is important for predicting the effects of animal food consumption on the environment and on human activities, such as farming. The wild boar is an omnivorous, opportunistic species whose diet is determined by the relative abundance of different types of foods. In general, the wild boar´s diet has been widely studied in the world, both as a native and invasive species, but little is known regarding food resource selection in the Monte Desert biome. Our study assessed the seasonal variation in the diet of wild boars, as well as the nutritional quality of consumed items. Further, we determined the diet selection of this species. Diet analyses were based on faecal samples collected over two seasons (wet and dry) during one year. Herbs were the most frequently consumed food item, with wild boars showing a selection for them in both seasons. The wild boar uses food resources according to seasonal availability (larger trophic niche breadth under higher plant diversity, as in the wet season). In turn, within each season, it selects items of high forage quality and high carbohydrate contents. In conclusion, this foraging strategy enables wild boar to maximize energy budget through food selection in order to survive in a semi-arid environment such as the Monte Desert.

Author affiliation: Cuevas, Maria Fernanda. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Mendoza. Instituto Arg. de Invest. de Las Zonas Aridas;

Author affiliation: Ojeda, Ricardo Alberto. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Mendoza. Instituto Arg. de Invest. de Las Zonas Aridas;

Author affiliation: Dacar, Maria Ana. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Mendoza. Instituto Arg. de Invest. de Las Zonas Aridas;

Author affiliation: Jaksic, Fabian. Universidad Catolica de Chile. Center For Advanced Studies In Ecology And Bidiver;

Abstract:

Geologic events promoting the aridization of southern South America contributed to lineage divergences and species differentiation through geographic (allopatric divergence) and biotic and abiotic factors (ecological divergence). For the genus Anarthrophyllum, which is distributed in arid and semi-arid regions of Patagonia, we assessed how these factors affected species diversification and reconstructed its possible biogeographic history in South American arid environments. Sequences were obtained from two molecular markers: the ITS nuclear region and the trnS-trnG plastid region. Using Parsimony, Maximum likelihood and Bayesian inference individual gene trees were reconstructed, and a species tree was obtained using multi-species coalescent analysis. Divergence times among species were estimated using secondary calibrations. Flexible Bayesian models and stochastic character mapping were used to elucidate ancestral geographic distributions and the evolution of the floral and vegetative phenotypes in the genus. Gene trees and species tree analyses strongly support Anarthrophyllum as monophyletic; all analyses consistently retrieved three well-supported main clades: High Andean Clade, Patagonian Clade 1, and Patagonian Clade 2. Main diversification events occurred concomitant with the Andean uplift and steppe aridization; the Andean mountain range possibly acted as a species barrier for the High Andean Clade. Vegetative traits showed adaptations to harsh climates in some clades, while pollinator-related floral features were associated with independent diversification in bee- and bird-pollinated clades within both Patagonian Clades. In conclusion, evolutionary and biogeographic history of Anarthrophyllum resulted from the action of ecological, historical, and geographic factors that acted either alternatively or simultaneously.

Author affiliation: Achimón, Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Author affiliation: Johnson, Leigh. University Brigham Young; Estados Unidos

Author affiliation: Cocucci, Andrea Aristides. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Author affiliation: Sersic, Alicia Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina. Universidad Nacional de Córdoba; Argentina

Author affiliation: Baranzelli, Matias Cristian. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina