Pampa Research Articles

Assessing puma habitat suitability in Uruguay’s Grasslands: exploring source-sink dynamics and conservation implications

ABSTRACT Pumas (Puma concolor) have a broad geographic range across the Americas and are globally listed as Least Concern. However, in Uruguay’s Pampas Grasslands, they are considered Data Deficient and regionally endangered in Argentina and Brazil. Understanding the distribution and population status of pumas is crucial for their conservation. This study examines puma occurrence in Uruguay’s Grasslands within a regional context, assessing habitat suitability and recent land use changes. Using a Species Distribution Model (SDM) in MaxEnt with 224 occurrence records (1999–2011) and bioclimatic and topographic predictors, we found intermediate habitat suitability in the Pampas Grasslands, indicating a naturally sparse puma population. The highest suitability was along riverbanks and riparian areas. Recent land use changes have transformed suitable habitats into areas less likely to support pumas, affecting a significant portion of Uruguay’s land. Our results suggest source-sink dynamics, where Uruguayan puma records likely represent dispersing individuals from established subpopulations in Eastern Argentina and Southern Brazil.

Exploring seed density and limiting similarity to reduce invasive grass performance for grassland restoration purposes

AbstractQuestionsControl of invasive species and seed addition are key steps in grassland restoration. Nevertheless, selecting seed mixes and seed quantities are hard tasks in restoration projects. An interesting idea is to design seed mixes using functional traits and create a community based on limiting similarity to overlap and outcompete the invader. We aimed to test the effect of two sown communities (one created to overlap the invader niche) and three seed sowing densities to reduce the performance of the invasive grass Eragrostis plana.LocationGreenhouse experiment in the Campos Sulinos grasslands region, Southern Brazil.MethodsWe created a bifactorial experiment. The first factor was the sown community, each composed of nine native grasses but with different proportions: (1) Limiting, based on limiting similarity, and (2) Balanced, where all species were sown at the same seed weight. We used leaf functional traits (Specific leaf area, leaf area, leaf dry matter content ) to design the Limiting community. The second factor was the seed density of native species, sowing twice (1) 1 g/m2, (2) 2 g/m2, and (3) 4 g/m2 (i.e., total density was 2, 4, and 8 g/m2). E. plana was sown once at 0.5 g/m2. Above‐ground and below‐ground biomass of all species were collected after nine months to assess the treatment effects.ResultsBiomass production of the invasive species was lower when sown with native species. Nevertheless, both sown communities did not differently affect the invasive biomass production. Higher seed density of native species resulted in lower invasive above‐ground biomass, but not below‐ground biomass. Three native species did not germinate, consequently, the established communities were quite different from those designed.ConclusionsThe low species germination limited our discussion about the use of limiting similarity to design seed mixes. High seed sowing density is a better approach when defining sowing strategies to compete with invasive grasses.

Dendroclimatology of Prosopis nigra in the Espinal woodlands, southeastern South America

This paper evaluates the dendrochronological potential of Prosopis nigra in the subtropical xerophytic forests of northeastern Argentina, an area of the Espinal forest particularly poor in dendrochronological records. Our study is based on tree-ring analyses of 23 cross sections providing a high-quality chronology (Rbar = 0.24 and EPS = 0.92). The mean annual radial increment recorded was 2.38 ± 1.51 mm. The inter-annual variability in the tree rings indicates that water availability from the previous winter to the current summer growing season is the major forcing on tree growth. Above-average rainfall and SPEI from July to February favored radial growth. Our results show for the first time the strong influence of both ENSO 3.4 and subtropical Atlantic SST variations, mediated by changes in local precipitation, on the growth of P. nigra in the Espinal. We concluded that P. nigra has great dendrochronological and dendroclimatological potential, since its rings are visible after careful polishing of the samples, and its inter-annual variations in radial growth are related to regional climate variability. These results can help improve our knowledge of the vulnerability of xerophytic forests to climate change in northeastern Argentina. In addition, this dendroclimatological study provides new proxy climate records for the Pampean grasslands, one of the most important food producing regions in the world.

Seasonal changes in habitat use and behavior of the threatened Pampas meadowlark Leistes defilippii

The Pampas grasslands’ biodiversity is severely threatened by habitat modification, as is the case for the Pampas meadowlark ( Leistes defilippii). Here we study the areas used by the species throughout the year in the Southern Pampas of Argentina, in association with seasonal changes in behavior, in an attempt to provide information for its effective conservation. We selected four grassland sites with livestock activities in which we studied vegetation characteristics and the abundance and behavior of the Pampas meadowlark, during breeding and non-breeding seasons. The species was absent in sites with higher bare ground cover and lower cover of >30 cm vegetation, and with high proportions of forb, shrub or exotic grass species. In those areas where the Pampas meadowlark was present during the breeding season, its abundance was higher where the grassland was entirely dominated by native grasses, and abandoned another site when the grassland became dominated by introduced plant species, after the breeding period. We are the first to report the behavior of a Pampas meadowlark population throughout an entire year with its seasonal changes. Our results and description of the behavior throughout the year highlight the importance of structural heterogeneity of the grasslands, determined by a low intensity of grazing, for the breeding of the Pampas meadowlark. Also, features associated with breeding habitat can’t predict the presence of flocks during the non-breeding season, as noted in our results for vegetation structure, but vegetation composition, food availability and landscape variables could play an important role in determining which areas serve as appropriate habitat during the non-breeding season, when large flocks search the grasslands for food. A better understanding of the habitat requirements and the use of space at different scales by the Pampas meadowlark will allow the identification of the most urgent and effective measures for its conservation.

Highly conserved and extremely variable: The paradoxical pattern of toxin expression revealed by comparative venom-gland transcriptomics of Phalotris (Serpentes: Dipsadidae)

Although non-front fanged snakes account for almost two-thirds of snake diversity, most studies on venom composition and evolution focus exclusively on front-fanged species, which comprise most of the clinically relevant accidents. Comprehensive reports on venom composition of non-front fanged snakes are still scarce for several groups. In this study, we address such shortage of knowledge by providing new insights about the venom composition among species of Phalotris, a poorly studied Neotropical dipsadid genus. Phalotris are known for their specialized venom delivery system and toxic venoms, which can cause life-threatening accidents in humans. We evaluate the venom-gland transcriptome of Phalotris, comparing the following three South American species: P. reticulatus for the Araucaria Pine forests, P. lemniscatus for the Pampa grasslands, and P. mertensi for the Brazilian Cerrado. Our results indicate similar venom profiles, in which they share a high expression level of Kunitz-type inhibitors (KUNZ). On the other hand, comparative analyses revealed substantial differences in the expression levels of C-type lectins (CTL) and snake venom metalloproteinases (SVMP). The diverse set of SVMP and CTL isoforms shows signals of positive selection, and we also identified truncated forms of type III SVMPs, which resemble type II and type I SVMPs of viperids. Additionally, we identified a CNP precursor hosting a proline-rich region containing a BPP motif resembling those commonly detected in viperid venoms with hypotensive activity. Altogether, our results suggest an evolutionary history favoring high expression levels of few KUNZ isoforms in Phalotris venoms, contrasting with a highly diverse set of SVMP and CTL isoforms. Such diversity can be comparable with the venom variability observed in some viperids. Our findings highlight the extreme phenotypic diversity of non-front fanged snakes and the importance to allocate greater effort to study neglected groups of Colubroidea.

Response of endophyte‐infected and endophyte‐free tall fescue plants to partial submergence at two developmental stages

AbstractTall fescue (Festuca arundinacea Schreb.) is a perennial C3 grass species usually associated with the endophyte fungus Epichloë coenophiala that enhances tolerance to biotic and abiotic stresses. Given that the proportion of infected tall fescue plants in the grasslands of the Flooding Pampa (Argentina) has been progressively increasing, it is proposed that endophytes confer tolerance to the stresses characteristic of that environment, especially flooding. Plants from a naturalized population and a commercial cultivar were grown, both with and without endophyte (wild type and AR584 respectively). The plants were subjected to two submergence treatments (i.e., control and partial submergence) in two development stages (5‐leaf stage and beginning of the elongation of internodes). Plant performance (aerial and root biomass, root aerenchyma formation, total root length and root diameter, proportion of reproductive tillers, number of panicles and seeds produced) and endophyte transmission to progeny were evaluated. Endophytes did not alter the ecological fitness of plants under partial submergence. Independently of the water condition, the symbiosis was linked to low biomass in plants from the naturalized population, while the opposite occurred in plants from the cultivar. Partial submergence did not affect the germination of the seeds produced, nor the transmission of the endophyte to the seedlings that originated from them. Our work suggests that the invasion ability of tall fescue in the Flooding Pampa grasslands is not related to an endophyte‐mediated improvement of plants to tolerate water excess.

Modeling population dynamics of invasive pines to optimize their control in native grasslands of Argentina

The spread of invasive alien species over natural environments has become one of the most serious threats to biodiversity and the functioning of ecosystems worldwide. Understanding the population attributes that allow a given species to become invasive is crucial for improving prevention and control interventions. Pampas grasslands are particularly sensitive to the invasion of exotic woody plants. In particular, the Ventania Mountains undergo the advance of alien woody plants; among which the Aleppo pine (Pinus halepensis) stands out due to the extension of the area it covers and the magnitude of the ecological changes associated to its presence. Using a model that describes the population dynamics of the species in the area, we evaluated the expected behavior of the population under different environmental conditions and different management scenarios. When the effect of stochastic fires was simulated, the growth rate was greater than 1 for all the frequencies considered, peaking under fires every nine years, on average. When evaluating the effect of periodic mechanical control of the adult population, the reduction in growth rate was insufficient, except for cutting intensities that significantly exceeded the current operational capacity of the area. Under prescribed fire scenarios, on the other hand, burning frequencies greater than seven years resulted in population reductions. The results highlight the importance of fire in regulating the population of P. halepensis in the Ventania Mountains, with contrasting effects depending on the frequency with which it occurs, which allows considering it as an effective environmental management option for the control of the species.

Towards a Monophyletic Infrageneric Circumscription of Adesmia DC. (Dalbergieae, Leguminosae): a Taxonomic Revision in Adesmia series Adesmia

The Adesmia clade comprises five genera, with Adesmia being the most diverse and speciose, and formerly containing 206 species and 37 varieties, distributed in two subgenera and 43 series. The genus inhabits almost exclusively the South American Arid Diagonal, which hosts some of the driest environments on Earth. Within Adesmia subgenus Adesmia, three series primarily inhabit the Pampa grasslands: series Muricatae, Bicolores, and Subnudae. These taxonomically complex series display overlapping morphological characters and geographical distribution ranges, and their monophyly has never been tested. We carried out a thorough systematic study of the three series, combining Maximum Likelihood and Bayesian analyses of 87 sequences of nrITS DNA of Adesmia. Beased on our phylogenetic results, we provide a taxonomic revision of the species in series Muricatae, Bicolores, and Subnudae. Series Subnudae and Bicolores are nested within series Muricatae, and synonymization of the first two under series Muricatae is here proposed. Three clades containing species with geographical and morphological coherence were unraveled inside Adesmia. Three varieties are elevated to species level, and another six were reduced to synonyms. Seven lectotypes and one neotype are proposed. We recognize 21 species in the new circumscription of Adesmia series Muricatae, and provide a species identification key, descriptions, illustrations, and maps, as well as comments on phenology, taxonomy, etymology, distribution, and habitat. We also present conservation assessments for the species of the series.

Comparative analysis of antibiotic susceptibility patterns and clinical features of mucoid and non-mucoid Pseudomonas aeruginosa infections: a retrospective study.

Pseudomonas aeruginosa (PA) is a prevalent opportunistic pathogen that has close associations with both acute and chronic infections. However, there exists an insufficiency of accurate and comprehensive data pertaining to the antimicrobial susceptibility patterns and clinical characteristics of both mucoid and non-mucoid strains of PA (mPA and non-mPA, respectively). From January 1, 2021 to December 31, 2022, a thorough retrospective study was carried out to examine and compare the antibiotic susceptibility test outcomes and clinical characteristics of hospitalized patients with mPA and non-mPA infections. This study investigated a cohort of 111 patients who were diagnosed with mPA infections, as well as 792 patients diagnosed with non-mPA infections. Significant demographic disparities, including gender (p < 0.001), age (p < 0.001), length of hospital stay (p < 0.001), diabetes (p = 0.043), and hypertension (p < 0.001), are evident between the mPA and non-mPA groups. The mPA group commonly necessitates hospitalization for respiratory system diseases, whereas the non-mPA group is associated with concomitant cardiovascular and cerebrovascular diseases. The mPA group demonstrates lower utilization rates of medical devices, such as Foley catheter (p < 0.001), nasogastric tube (p < 0.001), mechanical ventilation (p < 0.001), tracheostomy (p < 0.001), arterial and venous catheterization (p < 0.001), and exhibits superior organ function status, including lower incidences of hypoalbuminemia (p < 0.001), septic shock (p < 0.001), liver dysfunction (p < 0.001), renal failure (p < 0.001), and respiratory failure (p < 0.001). The non-mPA group is more vulnerable to infection with two or more bacterial pathogens compared to the mPA group, with the non-mPA group frequently resulting in Enterobacteriaceae infections and the mPA group being associated with fungal infections. Variations in antibiotic sensitivity are noted for Amikacin (p < 0.001), Ciprofloxacin (p < 0.001), Cefepime (p = 0.003), and Levofloxacin (p < 0.001) in antibiotic susceptibility testing, with resistance patterns closely tied to specific antibiotic usage. There are significant demographic characteristics, clinical manifestations and antibiotic susceptibility between mPA and non-mPA infections. It is crucial to emphasize these characteristics due to their significant role in preventing and treating PA infections.

Flying singers: spatio-temporal distribution and acoustic dynamics of two species of Carinetini (Hemiptera: Cicadidae) cicadas in sympatry

Abstract The natural history of Neotropical cicadas is poorly understood. Here, we describe comparatively the spatio-temporal distribution and acoustic dynamics of two Carinetini cicadas in sympatry: colourful-cicada, Carineta diardi, and eryngo-cicada, Guaranisaria llanoi. Males of both species emit conspicuous acoustic signals during flight, a rare behaviour in cicadas. Although sympatric and synchronic, these species are not syntopic, occurring in different habitats: colourful-cicada occurs in Atlantic Forest and eryngo-cicada in native Pampean grasslands. Vertical stratification also occurs: colourful-cicada flies, sings, and copulates along the forest edge and canopy (above 2 m), while eryngo-cicada flies, sings, and copulates only in open areas (below 1 m), performing directional flights between the ‘Gravatá’ eryngo patches—a keystone plant species used as shelter, and calling and reproduction site. Acoustic repertoires vary between species: colourful-cicada presents two types of signals (flying and calling songs) and eryngo-cicada has four types (flying, calling, courtship, and wing-flicks emitted by the females). Furthermore, acoustic differences between species were found in the flying songs, but no specific differences were found in the peak frequency of their calling songs. These results show that spatial use of ‘flying singer’ cicadas can vary in habitat, providing coexistence in sympatry.

Ecosystem stability of temperate grasslands in response to variability of hydrological conditions

AbstractThe relationship between biodiversity and the stability of ecosystem functioning over time has been widely studied. The current global context has refloated this topic for biodiversity's role in buffering the effects of different disturbances. In general, the results of these studies show that ecosystem functioning is more stable over time in more diverse systems. However, these results are derived from empirical research on small‐scale studies, where species and disturbances conditions are manipulated. In this work, we used climate and floristic information data obtained from surveys over an extended period on Flooding Pampa grasslands (Argentina) with a remotely sensed indicator of the stability of net primary productivity at a regional scale over a broad temporal range to evaluate the relationship between species diversity and the stability of ecosystem functioning under different water conditions. We found a close correlation between Normalized Difference Vegetation Index responses of natural grasslands and climate variability in the study area. Besides, grasslands with higher species richness and diversity showed greater stability in ecosystem functioning at different water conditions. The results obtained could be relevant in natural resource management for the close relationship between diversity–stability in a local and regional productive context characterized by a simplified landscape of space and time.

Restoration of invaded temperate grasslands: species phenology adds to microsite and seed availability

AbstractQuestionsRestoring diversity in temperate grasslands requires eliminating invaders and recovering different native phenological groups. Clipping and seed addition promote native grass recovery, but these effects could depend on the phenological overlap between invaders and native species. We evaluated the importance of the interaction between two types of clipping, species phenology and sowing to restore temperate grasslands invaded by the cool‐season forage species Festuca arundinacea (tall fescue).LocationFlooding Pampa grassland (Buenos Aires, Argentina).MethodsWe applied selective and non‐selective clipping on tall fescue during the peak growing season, combined with the sowing of native cool‐ and warm‐season grasses. Plant species cover was estimated visually for 3 years; species were categorized by functional groups. Moreover, through emergence trials, we evaluated whether the soil seed bank had been impoverished by invasion.ResultsRegardless of selectivity, clipping decreased tall fescue cover by 12%/year, which reduced microsite limitation. Consequently, total native richness increased by 5 spp./year and cover increased from 3% to 50% by the last experimental year, independent of clipping type. Moreover, native warm‐season grasses, the group with the least phenological overlap with invaders, increased by nearly 25% in cover and by 5 spp./m2 with clipping and independently of sowing. Contrarily, native cool‐season grasses, with more phenological overlap with invaders, increased 5% with propagule addition. Furthermore, the seed bank was enriched with tall fescue and depleted of cool‐season grasses.ConclusionsOur results reveal that overcoming microsite limitation is a necessary condition to restore plant diversity in grassland invaded by tall fescue. Nevertheless, seed limitation and phenological overlap may be particularly important to restore the diversity of some native functional groups of plants. Considering the phenology of species can help to identify either clipping targets or phenological groups to be sown when restoring native diversity.

A new analytical framework for Maxent species distribution models unveils complex spatiotemporal suitability patterns for two migratory seedeaters (Aves: Sporophila) of conservation concern

Maxent species distribution models (SDMs) for rare, migratory taxa can be hindered by methodological and analytical issues. To overcome these problems, we developed an analytical framework to build SDMs for key stages of the annual lifecycle of the Marsh Seedeater and the Black-bellied Seedeater, two Neotropical grassland bird species of conservation concern. Occurrence data were compiled from multiple sources and ten environmental variables were used as predictors. We built SDMs with different spatial partitions, feature classes, and regularization multipliers, and devised a procedure to select models with high discrimination ability, low overfitting, statistically significant performance metrics, and high biological realism. From a total of 992 SDMs, 22 fully met the selection criteria for both species. These selected SDMs were equally or less overfit than non-selected ones and were mostly trained with the checkerboard 2 and n − 1 jackknife partitions. For each modeling scenario, we projected and interpreted composite models that emphasized areas of both consensus and divergence across individual predictions, rather than choosing a single model from the set of final SDMs. In the breeding season, areas of highest suitability occurred in restricted, disjunct sectors of the Campos and Pampas grasslands for the Marsh Seedeater and the highland grasslands of southern Brazil for the Black-bellied Seedeater. In the winter, high suitability for the Marsh Seedeater occurred in the western and northern Cerrado and the Pantanal, while in the spring migration, high suitability for the Black-bellied Seedeater was mostly concentrated in the southeastern portion of the Cerrado. The restricted breeding distribution of the Black-bellied Seedeater suggests that its conservation status should be reviewed. Both species shift their climatic niches and track their habitats throughout the year, responding to a few topographic, land-use, and climatic variables that represent different niche components. By addressing major modeling issues in a three-step model selection procedure, we were able to project precise and biologically interpretable SDMs with the level of complexity required for each modeling scenario. Our framework is readily replicable and can be used to unravel intricate spatial suitability patterns of organisms whose distribution undergoes temporal shifts throughout the year.

Using 137Cs and 210Pbex to assess soil redistribution at different temporal scales along with lithogenic radionuclides to evaluate contrasted watersheds in the Uruguayan Pampa grassland

The use of environmental radionuclides in soil monitoring has made it possible to establish erosion rates. The combined use of 137Cs and 210Pbex is a common approach for determining mean annual erosion rates retrospectively in two different time windows; 137Cs in the past 50–60 years whereas 210Pbex provide a longer period up to 100 years. However, these radionuclides have contrasting sensitive behaviors, 210Pbex is able to be more sensitive to recent redistribution events of its last period of disintegration (22.3 yr) than 137Cs, being more sensitive to the past erosion and depositional events.This work studies soil redistribution rates at different temporal scales and the variability of lithogenic radionuclides by contrasting two watersheds with different land uses. The watersheds are Arroyo del Arbolito (AAW) and Cañada del Horno (CHW), both located near the Baygorria hydroelectric dam reservoir in Uruguay. Erosion rates obtained with 137Cs and 210Pbex using the MODERN conversion model for both watersheds showed that there are no significant differences for 210Pbex estimates, which suggests that the land management practices for both watersheds in the last twenty years do not differ and the erosion rates remained the same as the earlier period. However, significant differences were found for erosion estimated by using 137Cs in CHW vs AAW (p ≤ 0.05) and cultivated vs. natural pasture (p ≤ 0.001), which indicates that the main erosion events occurred further in the past. Furthermore, these changes in erosion estimated using both isotopes coincide with changes in land use and land management, from tillage-based practices in the past to the predominance of no-tillage since the early 2000 s. This change in soil management resulted in a reduction of approximately 50% in soil loss in those cultivated areas since 1965. In AAW, 51.7% of the sampled points exceeded the tolerable erosion rate (7 Mg.ha−1.yr−1) estimated using 137Cs, whereas for 210Pbex, 37% of the sampled points exceeded this limit. For CHW, 63.6% of the sampled points exceeded the tolerable erosion limit (9 Mg.ha−1.yr−1) estimated by using 137Cs, whereas for 210Pbex, 34.2% exceeded this limit. Our results suggest that the variation of lithogenic radionuclides by erosion is dependent on soil type and erosion magnitude. This study, which describes the use of two fallout soil radiotracers, provides new insights into the impact of land use conversion on soil degradation in the Pampas grassland ecosystem.

The relative role of climate and biotic interactions in shaping the range limits of a neotropical orchid

AbstractAimThe centre‐periphery hypothesis (CPH) explains the decline of species abundance towards range limits and how this is driven by increasing ecological marginality. So far, most studies testing the CPH have focused on abiotic factors contributing to marginality, while the role of biotic interactions in limiting species distribution has been neglected. Here, we investigate both drivers' roles in restricting an orchid's range along a broad environmental gradient.LocationAtlantic Forest and Pampas grasslands (south and southeastern Brazil).TaxaSand dune orchidEpidendrum fulgens(Orchidaceae).MethodsWe integrated empirical data on geographical distribution, pollinator richness and genetic diversity along the entire range of the species to investigate whether range limits match niche limits and whether habitat suitability declines towards low‐ and high‐latitude species ranges. We performed niche models to predict niche limits and used polynomial and linear regression models to investigate the associations between ecological niche and species range as well as to test the relationship between genetic‐derived metrics and the geographical and ecological distances.ResultsEcological conditions become more marginal towards the edges of theE. fulgensrange, with an abrupt variation in precipitation. While pollinator richness increases habitat suitability ofE. fulgensin the low‐latitude edge range, climate has primarily shaped the species' high‐latitude limit. Genetic diversity within populations decreases, while genetic differentiation increases towards both margins, although with a more consistent pattern for the low‐latitudinal component.Main ConclusionsThis study corroborates the predictions of CPH regarding ecological and genetic patterns of variation in space and highlights distinct factors limiting geographical distribution at the opposite margins of a latitudinal and narrowly distributed species. This improves our understanding on how biotic and abiotic variables limit species distribution ranges along latitudinal gradients in an extremely diverse and vulnerable tropical ecosystem, with potential for informing conservation practices.

Nest‐site features influence nest survival of the Hellmayr's pipit in extensive cattle‐grazed grasslands

AbstractThe Pampas Grasslands in South America have been almost completely transformed by urbanization and agriculture. Many grassland birds persist only in extensive natural pasturelands, which are under constant pressure from fragmentation, cattle‐grazing, and exotic plant species. Identifying which habitat features affect bird breeding success is important for their conservation in altered habitats, although few studies have been conducted in the Pampas Grasslands. We analyzed the influence of habitat features on the daily nest survival rates (DSR) of the Hellmayr's pipit (Anthus hellmayri), a grassland passerine endemic to South America, in a cattle‐grazed grassland. We evaluated the effects of vegetation features at a nest‐site scale, proximity to habitat edges, cattle density, and temporal factors. During 3 breeding seasons (2017–2020), we confirmed the fate of 90 nests, 25 of which were successful (27.8%). Predation was the most common cause of failure (80%), followed by weather‐induced abandonment (10.8%). Average DSR was 0.9106, with a cumulative survival probability of only 7.4%. The best model indicated that DSR was higher in nests adjacent to grass clumps than in those placed in depressions and followed a quadratic trend with nest age. Clump nests may be better protected from aerial predators and rainfall; hence pipits could be more successful in areas with more grass clumps. The very low nest success raises concern regarding the value of these grazing fields as breeding habitats; we urge authorities and landowners to increase conservation efforts in the remaining natural grasslands in the Pampas.

Distribution patterns and habitat preferences of medium and large mammals of the order Rodentia in the Carcarañá river basin, Southern Santa Fe province, Argentina

This contribution analyzes the distribution patterns and habitat preferences of wildlife in highly anthropized environments. Considering that the pampas grasslands are one of the most modified natural ecosystems in the world and that both the capybara (Hydrochoerus hydrochaeris Linnaeus, 1766) and the coypu (Myocastor coypus Molina, 1782) have historically been some of the most characteristic mammals of this ecosystem, it is from these two species that the environmental variables that best explain their distribution and affectation will be analyzed.

Assessing multiple limiting factors of seasonal biomass production and N content in a grassland with a year-round production.

There is little evidence on the extent that multiple factors simultaneously limit ecosystem function of grasslands with year-round production. Here we test if multiple factors simultaneously limit (i.e., more than one factor at a time) grassland functioning in different seasons and how they interacted with N availability. In a Flooding Pampa grassland, we ran a separate factorial experiment in spring, summer, and winter with several treatments: control, mowing, shading, P addition, watering (only in summer), and warming (only in winter), each of them crossed with two nitrogen treatments: control and N addition. Grassland functioning was assessed by aboveground net primary productivity (ANPP), green and standing dead biomass, and N content at the species group level. Out of 24 potential cases (three seasons by eight response variables), 13 corresponded to just one limiting factor, 4 to multiple limiting factors, and the other 7 to no evidence of limitation. In conclusion, grassland functioning in each season was most often limited by just one factor, while multiple limiting factors were rarer. Nitrogen was the prevailing limiting factor. Our study expands our knowledge of limitations imposed by factors associated with disturbance and stress, such as mowing, shading, water availability, and warming in grasslands with year-round production.

Composition and phylogenetic structure of Pampean grasslands under distinct land use and presence of alien species

Composition and phylogenetic structure of Pampean grasslands under distinct land use and presence of alien species

Inexorable land degradation due to agriculture expansion in South American Pampa

From 1985 onwards, South America has undergone a major expansion in agriculture at the expense of native vegetation (for example, native Pampa grassland). As an emblematic crop, the surface area cultivated with soybeans has increased by 1,000% between 1990 and 2020 in Uruguay. The environmental consequences of this massive land-use conversion on soil degradation remain poorly documented, although agriculture expansion is projected to continue to increase in the coming years in South America. In this study, sediment cores were collected in reservoirs located downstream of two contrasted agricultural catchments draining the Rio Negro River (Uruguay) to reconstruct the sediment dynamics and the sources of erosion associated with this expansion. Results demonstrated the occurrence of two periods of acceleration of sediment delivery since the 1980s. The first period of acceleration was recorded in the mid-1990s and was related to afforestation programs. The second and larger acceleration phase was recorded after 2000 during the soybean crop expansion. This period was marked by a greater supply of sediment from the native grassland source, highlighting the impact of agriculture expansion at the expense of native vegetation. Conservation measures should therefore be urgently taken to preserve biodiversity and soil functions in this region. The impacts on soil degradation of the massive land-use conversion of South American Pampa grasslands to agriculture are not well documented. This study estimates, over the period 1982–2019, the impacts of such conversion on the sediment cascade and how soil and water resources are affected as a result.