Interactions among grasses, shrubs, and herbivores in Patagonian grass-shrub steppes

The Patagonian shrub steppe, as most Patagonian ecosystems, is dominated by tussock grasses and shrubs. Our main objective was to review the ways in which grasses and shrubs interact and how this affects the structure and functioning of the steppe and discuss the impact of grazing on them. Water is the main limiting resource in the Patagonian shrub steppe. Competition and facilitation control grass and shrub density and distribution. Introduction of sheep since the beginning of the century may have affected vegetation and ecosystem structure and functioning and modified the grass-shrub relationships. We use a simple conceptual model to suggest how sheep grazing can modify the result of competition and the grass/shrub balance in ecosystems that show different levels of degradation. Additionally, grazing may disrupt the current two phase organization of vegetation and therefore may radically affect the ecosystem functioning of the steppe

Biozones of Patagonia (Argentina)

We present a classification of Patagonian ecosystems based on functional attributes derived from the seasonal curves of Normalized Difference Vegetation Index (NDVI), calculated from spectral data provided by the NOAA/AVHRR satellites. The attributes used were the annual integral, the relative range of NDVI, and the date of maximum NOW. These attributes capture critical aspects of the seasonal dynamics of carbon gains and allow for a good description of the spatial heterogeneity of ecosystem function in temperate areas. Our analysis defined 12 biozones that capture current ecosystem functioning. The units defined showed a good agreement with previously defined phytogeographical provinces. Mapping biozones based on attributes derived from satellite data does not require assumptions on the relationship between vegetation units and environmental features. This reduces the errors associated to the lack of correlation between the vegetation and environmental features

The climate of Patagonia general patterns and controls on biotic processes

In this article we review the main characteristics of the Patagonian climate, the spatial and temporal patterns of the most important climatic variables, and the influence of climate on ecosystem processes. The winter distribution of precipitation determines an asynchrony between the wet and the growing season in Patagonia. The amount of water that can be transferred from the wet season to the growing season depends mainly on the physical characteristics of the soil. In the semiarid steppe of Chubut, drainage accounted for 10% of annual precipitation. Winter distribution of precipitation determines also an asynchronic dynamics of evaporation and transpiration fluxes. The ENSO phenomenon have a significant impact on regional precipitation. In central-west Patagonia, spring precipitation (September to November) was lower than normal during La Niña events and greater than normal during El Niño events. From December to February the opposite pattern can be observed: higher than normal precipitation during La Niña events and lower than normal precipitation during El Niño events. The impact of this phenomenon on the seasonal temperature was not as clear as for precipitation. We did not detect any temporal trends in annual precipitation for the period 1961-1996. The phenology of carbon gains is quite homogeneous in Patagonia. Most of the region showed a peak of production in November, when, simultaneously, water availability and temperature are high. Toward the west, production peaked later (December). Deciduous forests showed the peak in January and February

Modelos en ecología

Los modelos suelen estar rodeados por un “halo de misterio “ que restringe su uso. Nuestro objetivo es desmitificarlos, a fin de promover su difusión en la solución de los variados problemas que afrontan quienes deben manejar ecosistemas. Los puntos centrales de este artículo son los conceptos de modelo como simplificación de un sistema y de sistema como todo conjunto cost dos o más partes interrelacionadas. Del análisis de esos conceptos se deduce que los problemas básicos, tanto para construir como para usar modelos, son la definición del sistema y la identificación de sus partes y de las interacciones entre ellas. No existe un único tipo de modelos ni un único método para construirlos: la estructura, el desarrollo y los alcances de cada modelo dependen estrechamente del problema que se quiere resolver con él. A modo de ejemplo se detallan las diferentes etapas que se siguieron para la construcción de un modelo, utilizado confines didácticos, que simula la dinámica de la biomasa de los pastos en la estepa del Sudoeste de Chubut y su variabilidad en respuesta a diferentes condiciones ambientales. Se discute la necesidad de reformular supuestos básicos del modelo afín de que sus resultados resulten más acordes con el conocimiento actual del sistema estudiado.Models are usually surrounded by an atmospliere of mistery that limits their use. Our aire is to end this myth in order to promote the diffusion of models as tools to solve the problems faced by ecosystem managers. The retain points of this article are the concepts of a model as a simplification of a system, and system as a whole that contains at least two interrelated parts. The three basic problems of constructing and using models, which can be deduced from the analysis of those concepts, are the definition of the system, their parts, and the interactions among them. There is not ti single kind of model or method to construct it: the structure, the construction, and the achievements of each model closely depend on the problem to be solved with it. As an example, this paper details the different steps followed to construct a model, used with educational purposes, which predicts the biomass dynamics of the steppe of SW Chubut, Argentina, and its variability in response to environmental conditions. We discuss some discrepaticies between the results of the model and our knowledge of the system, and show how some of the basic assumptions must be reformulated

A Concept Map of Evolutionary Biology to Promote Meaningful Learning in Biology

Is it possible to teach biology without mentioning evolution? The answer is yes, but it is not possible for students to understand biology without the evolutionary context on which the meaning and intellectual value of biological concepts depend. Meaningful learning of evolution requires (1) that the students incorporate new knowledge into a cognitive structure linked with higher-order concepts; (2) a well-organized knowledge structure; and (3) a positive emotional attachment and identification (affective commitment) to the subject by the learner. Concept maps are useful tools in meaningful learning. We present a concept map that organizes concepts of history of life and the processes that generate it, and the hierarchical relationships among them. Biological evolution is a compelling account of life on Earth and of human origins. It constitutes a unifying explanatory framework that can generate a powerful affective commitment to the subject. The concept map provided here is tied to the Next Generation Science Standards (NGSS).Facultad de Ciencias Naturales y Muse

Few multiyear precipitation-reduction experiments find a shift in the productivity-precipitation relationship

Well-defined productivity–precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity–precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation–reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effects of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation–manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity–precipitation relationship downward the spatial fit. The majority of experiments (72%) showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land-model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation–reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid

Connectivity: insights from the U.S. Long Term Ecological Research Network

Ecosystems across the United States are changing in complex and surprising ways. Ongoing demand for critical ecosystem services requires an understanding of the populations and communities in these ecosystems in the future. This paper represents a synthesis effort of the U.S. National Science Foundation-funded Long-Term Ecological Research (LTER) network addressing the core research area of “populations and communities.” The objective of this effort was to show the importance of long-term data collection and experiments for addressing the hardest questions in scientific ecology that have significant implications for environmental policy and management. Each LTER site developed at least one compelling case study about what their site could look like in 50–100 yr as human and environmental drivers influencing specific ecosystems change. As the case studies were prepared, five themes emerged, and the studies were grouped into papers in this LTER Futures Special Feature addressing state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the “connectivity” theme and has examples from the Phoenix (urban), Niwot Ridge (alpine tundra), McMurdo Dry Valleys (polar desert), Plum Island (coastal), Santa Barbara Coastal (coastal), and Jornada (arid grassland and shrubland) sites. Connectivity has multiple dimensions, ranging from multi-scalar interactions in space to complex interactions over time that govern the transport of materials and the distribution and movement of organisms. The case studies presented here range widely, showing how land-use legacies interact with climate to alter the structure and function of arid ecosystems and flows of resources and organisms in Antarctic polar desert, alpine, urban, and coastal marine ecosystems. Long-term ecological research demonstrates that connectivity can, in some circumstances, sustain valuable ecosystem functions, such as the persistence of foundation species and their associated biodiversity or, it can be an agent of state change, as when it increases wind and water erosion. Increased connectivity due to warming can also lead to species range expansions or contractions and the introduction of undesirable species. Continued long-term studies are essential for addressing the complexities of connectivity. The diversity of ecosystems within the LTER network is a strong platform for these studies

Expert perspectives on global biodiversity loss and its drivers and impacts on people

Despite substantial progress in understanding global biodiversity loss, major taxonomic and geographic knowledge gaps remain. Decision makers often rely on expert judgement to fill knowledge gaps, but are rarely able to engage with sufficiently large and diverse groups of specialists. To improve understanding of the perspectives of thousands of biodiversity experts worldwide, we conducted a survey and asked experts to focus on the taxa and freshwater, terrestrial, or marine ecosystem with which they are most familiar. We found several points of overwhelming consensus (for instance, multiple drivers of biodiversity loss interact synergistically) and important demographic and geographic differences in specialists’ perspectives and estimates. Experts from groups that are underrepresented in biodiversity science, including women and those from the Global South, recommended different priorities for conservation solutions, with less emphasis on acquiring new protected areas, and provided higher estimates of biodiversity loss and its impacts. This may in part be because they disproportionately study the most highly threatened taxa and habitats