Patagonian Steppe Research Articles

Midsummer Trophic Overlap Between Guanaco and Sheep in Patagonian Rangelands

Diet overlap estimation among species is important to understand interspecific interactions. Through these interactions, one species may extinguish others through competition or adapt through mechanisms such as resource partitioning. The introduction of domestic herbivores in a native assemblage may introduce competition for resources with wild herbivores. In southern Patagonian steppes, guanaco (Lama guanicoe) populations are increasing after a drastic demise during the past century. This is occurring in protected areas and extensive ranching areas for sheep, and in the latter ranchers have rising concerns regarding competition. In this observational study, we measured diet overlap, food selection and preferences, and niche width for guanaco and sheep to compare use of food resources during the summer season. Feces were analyzed through microhistological technique to determine sheep and guanaco diets. Diets of guanaco and sheep were dominated by tussock grass (Festuca gracillima, sheep > 60%, guanaco > 50%), the most abundant plant species. Although food niche widths, measured through Levin’s Index, were narrow, guanaco presented the broadest niche (P < 0.001). Of the 17 identified plant species present in guanaco and sheep diets, 5 were always selected by both ungulates and 1 was always avoided at the four study sites. Overlap between diets was high (> 0.90), evidencing potential competition. In addition, diet overlap coupled with our results of small variation in use and selectivity of food resources suggest the absence of resource partitioning. Therefore, both species might share resources or coexist, possibly due to high availability or spatial distribution of food resources and guanaco resilience to cope with numerically dominant competition from sheep. These findings offer new insight into the understanding of these species’ interactions. It is also a management challenge to emerging wild and domestic herbivores interactions, as well as livestock production concerns at large.

Strategies to persist in the community: Soil seed bank and above‐ground vegetation in Patagonian pine plantations

AbstractQuestionsIn terms of biodiversity conservation, forest plantations are often considered problematic because they usually have negative effects on natural ecosystems. Soil seed banks could play an important role in restoring vegetation that was originally present, by recruiting species that have disappeared above‐ground. We addressed this topic in plantations located in the Patagonian steppe by asking the following questions: Are richness, abundance and composition of steppe above‐ground vegetation and soil seed bank affected by plantations? Is species composition of the above‐ground vegetation and soil seed bank similar in plantations and in the steppe?LocationNW of Chubut Province, Patagonia, Argentina.MethodsWe selected three plantations located in the steppe, and delimited three sectors: steppe, plantation edge and plantation interior. We compared richness and abundance by species origin and growth form among sectors for the above‐ground vegetation and soil seed bank compartments, using generalized linear mixed models. We compared species composition for each compartment and between them using permutational multivariate analysis of variance and non‐metric multidimensional scaling.ResultsIn above‐ground vegetation, we found a decrease in richness and abundance, and changes in composition from the steppe to the plantation interior. Richness and abundance of the soil seed bank did not show differences among steppe and the plantation sectors, although composition was different among them. Above‐ground vegetation and soil seed bank species composition were always different; native perennial herbs and shrubs were predominant in the above‐ground vegetation while exotic annual herbs dominated the soil seed bank.ConclusionsOur findings suggest that plant recruitment from the soil seed bank would not be sufficient for restoring depleted species pools in the above‐ground vegetation of plantations. Therefore, actions promoting native species reestablishment and control of exotics should be considered to reach the aim of restoring biodiversity in former plantations.

Fish-processing effluent discharges influenced physicochemical properties and prokaryotic community structure in arid soils from Patagonia

Along the Patagonian coast, there are processing factories of marine products in land that produce fish-processing effluents. The aim of the present study was to assess the physicochemical properties and the prokaryotic community composition of soils receiving fish-processing effluent discharges (effluent site-ES), and to compare them with those of unaltered soils (control site-CS) in the arid Patagonian steppe. We analyzed soil prokaryotic communities (using amplicon-based sequencing of 16S rRNA genes), soil physicochemical properties and fish-processing effluent characteristics. Soil moisture, electrical conductivity (EC), total and inorganic C were significantly higher in ES than in CS (p < .05). Effluent discharges induced a decrease in the total number of operational taxonomic units (OTUs) and in the Shannon diversity index (p = .0009 and .01, respectively) of soil prokaryotic community. Proteobacteria, Actinobacteria and Acidobacteria were the dominant phyla in CS, while ES soil showed a more heterogeneous composition of phyla. Linear discriminant analysis (LDA) effect size (LEfSe) analysis showed that fish-processing effluent discharges promoted an enrichment of Firmicutes and Bacteroidetes, which are active contributors to organic matter mineralization, along with a decrease of oligotrophic phyla such as Acidobacteria, Chloroflexi, Armatimonadetes and Nitrospirae, commonly found in nutrient-poor arid soils. The concentrations of inorganic C and ammonium, the EC and the soil moisture explained 73% of the total variation within the community composition. Due to its salinity and nutrients, fish-processing effluents have potential mainly for native salt-tolerant plant irrigation, however the impacts of soil prokaryotic community shifts over plant growth remain to be determined.

Roles of the environment, vegetation and spatial structure in the species composition of the Heteroptera community

In the present study, we assessed the assemblages of terrestrial Heteroptera along a 500-km latitudinal and 500-km longitudinal gradient in the north of Argentine Patagonia and investigated the potential effects of the environment, vegetation factors and spatial structure on the community composition of terrestrial Heteroptera at regional scale. To identify the terrestrial Heteroptera assemblages and evaluate their association with different factors, we used multivariate analyses. A total of 840 samplings were carried out in 21 sites of three phytogeographic provinces (Patagonian steppe, Subantarctic province and Monte) along two sampling years. We captured a total of 2007 specimens, 1890 of which were identified to species and morphospecies level, and 57 of which were immature-stage specimens that could not be identified due to their unknown morphology and biology. We identified two distinct terrestrial Heteroptera assemblages: a) one from sites belonging to the Patagonian steppe and Subantarctic province and b) the other from sites belonging to the Patagonian steppe and Monte. The variation in the terrestrial Heteroptera assemblages explained mainly by Isothermality was significant and greater than that explained by the vegetation and the spatial structure. The results showed that, in northern Argentine Patagonia, the different Heteroptera assemblages are more associated with geographic areas with different environmental conditions than with areas with different vegetation types. The results also suggest that the variation in Heteroptera species composition at regional scale is driven by environmental variables related to thermal amplitude and precipitation.

Short-term responses to sheep grazing in a Patagonian steppe

Grazing modifies ecosystem function through direct effects on plants, but also through indirect effects mediated by floristic changes induced by grazing. Although both types of effects occur in the long term, only the direct effects are evident in the short term. We evaluated the short-term direct effects of sheep (Ovis aries) grazing on a Patagonian steppe during one growing season. We measured plant aerial cover in permanent transects located at increasing distances from a watering point in three paddocks with different stocking rates through the growing season. We also measured frequency of defoliation for vegetative and reproductive phases of different plant species located along these transects. Sheep grazing directly (a) reduced aerial cover and/or increased frequency of defoliation of certain preferred grasses and perennial forbs, (b) did not increase the aerial cover of any life form, but only the proportion of bare soil, (c) did not change the litter aerial cover, and (d) defoliated the flowers of even the least preferred shrub. Result a) was coincident with previous plant aerial cover long-term studies; but results (b) and (c) were contrary to long-term studies, probably because they resulted from indirect rather than direct grazing effects. Result (d) was not detected by long-term studies, probably because flower defoliation through grazing is undetectable when measuring shrub plant aerial cover. Our study showed that grazing has short-term direct effects mainly on the most preferred species. This could be useful for rangeland management and conservation of Patagonian steppes because short-term effects may be more easily reversible than long-term ones, and may provide early warning of rangeland condition deterioration.

Variable Hawk (Geranoaetus polyosoma) is a Rare Nesting Species in Santa Cruz Province, Southern Continental Patagonia, Argentina

In Argentina, the Variable Hawk (Geranoaetus polyosoma) inhabits the northwestern, central, and southern parts of the country, but current information on its breeding distribution and conservation status for most Argentine provinces is lacking. Raptor nest surveys in Santa Cruz Province (southern Argentine Patagonia) during the breeding seasons of 1980–1981 and 2008–2011, revealed six active nests (one in 1980, two in 2008, and three in 2010), plus one additional nest (in 2011) showing evidence of use earlier in the breeding season. Additional ornithological surveys in Santa Cruz Province between 1994 and 2018 revealed two more nests (one each in 2002 and 2004). Results of these combined surveys suggest that the Variable Hawk breeds in very low numbers in the southern continental Patagonian steppes, grasslands, and coastal biomes of Santa Cruz Province. This low density substantiates previous reports on the rarity of the species in this province and contrasts with findings from northeastern Patagonia, where it breeds at high densities. Low Variable Hawk breeding abundance in southern continental Argentine Patagonia is likely related to low prey diversity and abundance as well as anthropogenic activities. We recommend surveys be conducted of this hawk and its prey in different biomes throughout Patagonia.

Grazing pressure interacts with aridity to determine the development and diversity of biological soil crusts in Patagonian rangelands

AbstractGrazing is directly related to land degradation and desertification in global drylands. Grazing impacts on vascular plants, reasonably well‐known, depend on its intensity and are modulated by local aridity conditions. However, we do not know how the interplay of grazing intensity and aridity affect biocrusts, topsoil assemblages dominated by cyanobacteria, lichens, and mosses that provide key ecosystem services in drylands. Here, we determined how grazing affects biomass, total cover, and richness of biocrust structural types across a regional aridity gradient in the Patagonian steppe. On average, grazing by sheep reduced biocrust biomass, total cover and richness of structural types by 55, 90, and 59%, respectively. In general, high grazing pressures had a larger impact on biocrusts than moderate or light grazing pressures. For example, biocrust cover was reduced by 85, 89, and 98% by light, moderate, and high grazing pressures, respectively. Although a slightly different response to grazing was observed under low aridity conditions, these more benign climatic conditions did not compensate for the negative effects of trampling by domestic animals on biocrusts. Nonetheless, estimated biocrust recovery rates under medium aridity conditions were faster than previously thought: it took 24, 18, and 58 years to double biocrust biomass, total cover, and richness of structural types. Sheep cannot be just removed in Patagonian rangelands because the production of meat and wool represents the main local economic activity. But landowners must consider our results to protect the ecosystem functions and services provided by biocrusts for future generations to come.

Oribatid mites (Acari: Oribatida) from the Patagonian steppe, Argentina.

Knowledge of the oribatid mite community from Patagonian steppe is scarce compared with other environments, such as the Andean-Patagonian forest. In the present research we identified oribatid mites under different environmental conditions: two Patagonian steppe types (grass and shrub), two soil characteristics (bare and covered soil) and two different seasons (autumn and spring). A total of 42 species/morphospecies were found, 13 were new records for Chubut and one was a new record for Argentina. In view of its ecological role in soil formation, it is fundamental that knowledge about this fauna is enhanced in order to provide baselines for study and to aid further understanding about its ecology.

Small mammal species turnover in response to climatic variations during the Holocene in Patagonia: A paleolandscape reconstruction

The goal of this study was to document the effects produced by Holocene climatic changes on the composition of small mammals along the elevational gradient in the Somuncurá Plateau Protected Area, northern extra-Andean Patagonia. A bone sequence accumulated by the disintegration of owl pellets was analyzed with taphonomic, paleoecological, and paleoenvironmental purposes. The studied site is located near the boundary between the Southern Monte and the Patagonian Steppes, and the paleontological sequence encompasses the middle Holocene. Multivariate analyses were used to classify Holocene samples into a regional geographical pattern, following the elevational and vegetation gradients. Comparisons between fossil and recent owl pellet samples indicated that species composition differed substantially during the middle Holocene. The species recovered constitutes the current assemblages from the bunchgrass steppes at the higher elevations of the plateau and implies an extension of the Patagonian Steppe occupying areas currently under the Monte influence. This paleoenvironmental context would have been developed under lower temperatures and stronger westerly winds. With temperature as the main factor to the structuring of the small mammal communities in Somuncurá, both past and present, special attention must be paid to the design of conservation strategies for this Protected Area considering future scenarios of climate change.

Conspecific leaf litter and root competition inhibits shrub emergence in the Patagonian steppe

A critical stage in the establishment of new individuals is seedling emergence and litter is a main factor affecting this stage. Recent research found that adults of Chuquiraga avellanedae are over-dispersed. Among several mechanisms, this pattern might be due to the negative influences of adults on seedlings through root competition. We performed field and glasshouse experiments to evaluate (i) the effects of C. avellanedae leaf litter and root presence on the emergence of conspecific seedlings, and (ii) the effects of leaf litter type (C. avellanedae litter, inert litter, no litter) and seed burial depth (seed at the surface or buried) on the emergence of C. avellanedae and Nassella tenuis (dominant grass) seedlings. The field experiment demonstrated root competition from adult plants on shrub seedlings, reducing seedling emergence. However, the effect of root competition did not differ between microsites (under-shrubs vs. between-shrubs). We dismiss the effect of allelopathy because inert litter (i.e., plastic leaves) had the same negative effect as C. avellanedae litter, indicating a mechanical effect. The glasshouse experiment revealed a species-specific response of seedling emergence. C. avellanedae litter limits the emergence of conspecific seedlings but was neutral with regard to the emergence of grass seedlings (N. tenuis). No differences in root competition between microsites and reduction of shrub seedlings by litter suggest that the over-dispersed pattern found for C. avellanedae is caused, at least partially, by litter effects on seedling emergence.

Temporal and spatial variability in soil CO2 efflux in the patagonian steppe

Soil respiration is a major flux of CO2 to the atmosphere. Despite its significance there is a limited understanding of its magnitude, controlling factors and how it varies over time and space in arid ecosystems. We evaluated the temporal pattern of soil CO2 efflux and their response to rain pulses in a patagonian steppe, taking into account the spatial heterogeneity (bare soil and vegetated patches). We measured soil CO2 efflux in bare soil and vegetated patches along the year. We also analyzed physical and chemical soil traits, root density and heterotrophic bacterial count. Soil water content and temperature exhibited seasonal variability and it was larger in bare soil patches than in vegetated patches. Root density, organic matter and phosphorus were higher in vegetated patches than in bare soil. CO2 efflux was 48% higher in vegetated patches than in bare soil patches. Soil CO2 efflux decreased from summer to winter, reaching its maximum value (about 0.6 μmol m2 s−1) in spring. In both patch types, soil CO2 efflux was explained by the interaction between soil temperature and soil water content. Soil CO2 efflux also was positively correlated with soil root density. Bare soil and vegetated patches exhibited distinct response to a rain pulses. Vegetated patches were highly sensitive to rainfall events, generating a large CO2 pulse, returning to previous values after three days. Bare soil CO2 efflux did not exhibit significant changes after a rain pulse. In patagonian arid ecosystems, the seasonal variation in soil respiration is explained mainly by the interaction between soil temperature and water content. Bare soil patches had higher water content but lower root density resulting in lower soil CO2 respiration than vegetated patches. However, at ecosystem level the contribution of bare soil to total soil CO2 efflux was similar to the contribution of vegetated patches because bare soil cover is 65% in the study area. Changes in the number of small rain events as well as changes in plant cover could have large consequences on soil ecology and biochemistry in dry and heterogeneous ecosystems.

Evolutionary history of herbivory in the Patagonian steppe: The role of climate, ancient megafauna, and guanaco

Herbivory is an important ecological process than has influenced the evolution of grassland-savannah systems. The evolutionary history of herbivory largely determines how resilient plant communities are to herbivory, with communities evolving with a long history generally possessing plant adaptations that make them able to cope with such disturbance. Thus, the evolutionary history of herbivory can serve as an indicator of a system’s resilience to modern grazing. Determining this history, however, is problematic because quantitative measures of herbivory and knowledge of plant origin are needed over appropriate evolutionary time frames. Paleoecology offers a useful framework for assessing this evolutionary history of plant-herbivore interactions. The Patagonian steppe is a phytogeographic province of South America whose evolutionary history of herbivory has been debated. Past discussions have focused completely on the abundance of its sole large ungulate herbivore—the guanaco (Lama guanicoe Müller 1776)—since European colonization of the continent. Here we use a paleoecological approach to reconstruct the evolutionary history of herbivory and plant evolution in the Patagonian steppe over a much broader, geologic time frame (Cenozoic) to shed light on the matter. We examine the role of past climate, ancient megafauna, and guanaco in shaping the vegetation and briefly discuss how present land use may be misaligned with the steppe’s evolutionary history of herbivory.

At a Microsite Scale, Native Vegetation Determines Spatial Patterns and Survival of Pinus contorta Invasion in Patagonia

Research Highlights: The invasive species Pinus contorta, has become a new component of the vegetation in the Patagonian Steppe, invading the complex matrix of bare ground, tussock grasses and cushion plants. At a microsite scale, the type of native vegetation is one of the multiple factors determining the establishment of P. contorta and in some cases, increasing its survival, and as a result, the invasion of the species. Background and Objectives: The presence of trees, particularly pines, where they are naturally absent, represents a clear threat to Patagonian steppe ecosystems. Thus, understanding the interaction between pines and native plant species may be the key to understanding the invasion and applying management actions. Pinus contorta is considered one of the most aggressive among the pines species, with recognized impacts on regions in the southern hemisphere and Europe, and it is one of the main invaders in the Patagonian steppe. Our aim in this study is to determine the influence of surrounding vegetation on P. contorta spatial distribution, its establishment and future development in the Chilean Patagonia. Materials and Methods: We used point pattern analysis to determine the existence of spatial associations between P. contorta and the resident vegetation of the Patagonian steppe. Further, a seeding experiment was carried out to assess the influence of the surrounding vegetation during P. contorta establishment and first growing season. Results: We found that young P. contorta individuals are positively associated with the native cushion plant B. magellanica and also to tussock grasses. Seeding experiments showed that P. contorta is influenced by resident plant species during establishment and is able to establish on any ground cover type in the Patagonian steppe, but some resident plant species increase P. contorta survival chances. Conclusions: Pinus contorta is interacting with native vegetation and becoming an active component of the Patagonian steppe mosaic. Although pines can establish in any type of vegetation in the Patagonian steppe mosaics, native cushion and tussock grasses may be facilitating the process and promoting pine survival, allowing it to survive and thrive in this stressful environment.

Effect of population density on diet composition and dietary niche breadth of guanaco (Lama guanicoe, Müller 1776) in northeastern Patagonian steppes

The optimal foraging theory postulates that as animal population density increases, the progressive decline in preferred forage availability results in changes in diet composition and widening of dietary niche breadth. For sedentary guanaco populations, some authors proposed a mechanism of population density limitation below the environmental carrying capacity, mediated through territoriality. Under the optimal foraging theory, increased density would lead to changes in guanaco diet selectivity and composition. Conversely, under the self-regulation hypothesis, guanacos would not affect preferred forage availability and no differences in guanaco diet would be expected. We tested these contrasting hypotheses by assessing both the differences in the proportion of grasses and shrubs present in guanaco diet and dietary niche breadth at three contrasting densities in northeastern Patagonian steppes. We did not find guanaco density effects on preferred forage availability, grass-shrub proportions in the diet and diet selectivity. Guanacos showed a mixed diet composed by plant species of both high and low nutritional quality independently of population density. The lack of changes in diet composition suggests that guanacos did not perceive a restriction in forage availability in terms of either biomass or nutritional content, regardless the observed increase in population density.

Vertical aerosol distribution in the southern hemispheric midlatitudes as observed with lidar in Punta Arenas, Chile (53.2° S and 70.9° W), during ALPACA

Abstract. Within this publication, lidar observations of the vertical aerosol distribution above Punta Arenas, Chile (53.2∘ S and 70.9∘ W), which have been performed with the Raman lidar PollyXT from December 2009 to April 2010, are presented. Pristine marine aerosol conditions related to the prevailing westerly circulation dominated the measurements. Lofted aerosol layers could only be observed eight times during the whole measurement period. Two case studies are presented showing long-range transport of smoke from biomass burning in Australia and regionally transported dust from the Patagonian Desert, respectively. The aerosol sources are identified by trajectory analyses with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) and FLEXible PARTicle dispersion model (FLEXPART). However, seven of the eight analysed cases with lofted layers show an aerosol optical thickness of less than 0.05. From the lidar observations, a mean planetary boundary layer (PBL) top height of 1150 ± 350 m was determined. An analysis of particle backscatter coefficients confirms that the majority of the aerosol is attributed to the PBL, while the free troposphere is characterized by a very low background aerosol concentration. The ground-based lidar observations at 532 and 1064 nm are supplemented by the Aerosol Robotic Network (AERONET) Sun photometers and the space-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). The averaged aerosol optical thickness (AOT) determined by CALIOP was 0.02 ± 0.01 in Punta Arenas from 2009 to 2010.

Residential energy transition and thermal efficiency in an arid environment of northeast Patagonia, Argentina

We have studied changes in energy use and practices due to a program which partially replaced firewood by fossil fuels. The program has been running for nearly five years in rural dwellings in Patagonia Argentina, where limited provision of fuelwood and social vulnerability are found. As a case study we focused on the community of Laguna Blanca, Province of Río Negro, located in the Patagonian steppe. Dwellings are one-family houses which were built with no energy efficiency measures, exposing reinforced concrete structures, fired-clay bricks, metal roofs and single-glass windows to severe weather. Since 2014, a government program fully subsidized the refilling of Liquid Petroleum Gas (LPG) to vulnerable rural communities, which were provided with a 200-kg gas tank and a gas heater in each household. An expected decrease in the use of fuelwood was observed, along with a very high consumption of LPG (around 650 kWh/m2 year), which can be for the first time assessed due to the known amount of LPG provided. The lack of energy efficiency policies led to very high operational costs and environmental impacts. Based on the dwellings' characteristics, we have also found that the LPG subsidies saved in 2.2 years would return the investment for a thermal insulation that would reduce 50% the gas consumption and substantially improve comfort.

Role of Grazing Intensity on Shaping Arbuscular Mycorrhizal Fungi Communities in Patagonian Semiarid Steppes

Arbuscular mycorrhizal fungi (AMF) are vital for maintaining ecosystem structure and functioning and can be affected by complex interactions between plants and herbivores. Information found in the literature about how ungulate grazing affects AMF is in general contradictory but might be caused by differences in grazing intensities (GIs) among studies. Hence we studied how different GIs affect the composition, diversity, and abundance of AMF communities in a semiarid steppe of Patagonia. We predicted that 1) total AMF spore abundance (TSA) and diversity would decrease only under intense-grazing levels and 2) AMF species spore abundance would depend on their life-history strategies and on the GI. To test our predictions, we compared AMF communities among nongrazed (NG), moderately grazed (MG, 0.1–0.3 sheep ha1), and intensely grazed sites (IG, > 0.3 sheep ha1). GI was the most important factor driving changes in TSA and diversity, regardless of host plant identity. TSA, diversity, and evenness significantly decreased in IG sites but were not affected by MG. AMF species spore abundance varied depending on their life-history strategies and GI. Families with high growth rates like Glomeraceae and probably Pacisporaceae showed the highest spore abundance in all sites but decreased under IG. Species with higher carbon demands like Gigasporaceae showed low spore abundance and frequency in NG and MG sites and were absent in IG sites. In contrast, species with low growth rates, but efficient carbon usage, like Acaulosporaceae, showed low spore abundance in all sites but increased in IG sites compared with NG or MG sites. We conclude that intensification of grazing reduces AMF diversity and abundance, with the likely loss of AMF benefits for plants, such as improved nutrient and water uptake and soil aggregation. Therefore, sustainable grazing systems should be designed to improve or restore AMF communities, particularly in degraded rangelands, like the Patagonian steppes.

Effects of Introduced Plants on Diet and Seed Preferences of Pogonomyrmex carbonarius (Hymenoptera: Formicidae) in the Patagonian Steppe.

Invasive species may interact with resident species and disrupt previously established interactions, with effects on the whole community. If introduced seeds are selectively consumed by native granivores, this could limit the establishment or spread of invasive plants (biotic resistance), and reduce the predation pressure upon native seeds. We determined if the presence of introduced plants affects the diet and the seed preferences of the ant Pogonomyrmex carbonarius (Mayr) in a Patagonian steppe. We expected a higher proportion of introduced seeds in the diet of nests located in areas with a high abundance of introduced species (roadsides) than in nests located in low invaded areas. Diet composition was obtained by collecting items retrieved by workers to colonies and compared between areas of contrasting abundance of introduced species. Field-based choice experiments were performed to evaluate whether exotic seeds were preferred to native ones under a paired comparisons design. Native seeds predominated in the diet. A low proportion of introduced species were included only in colonies close to the road. Ants preferred native seeds to introduced ones, and showed a marked preference for seeds of the native grass Pappostipa speciosa (Trin. & Rupr.) Romasch. (Poaceae), typical of the Patagonian steppe. The presence of introduced plants had little influence on interactions of P. carbonarius with seeds in the Patagonian steppe. Therefore, this ant species would not exert a control on the studied introduced plants, illustrating a case of low biotic resistance to invasion by these species.

Simulation model suggests that fire promotes lodgepole pine (Pinus contorta) invasion in Patagonia

To best understand plant invasions and predict unexpected outcomes it is necessary to integrate information on disturbance, the local environment, and demography. Disturbance by fire has been shown to promote invasions worldwide, but precise interactions between fire, native and invading species remain unclear. Indeed, trade-offs exist between fire-induced mortality of seed sources and increased establishment, driving invasion outcomes. A positive feedback between lodgepole pine (Pinus contorta) invasions and fire has been identified but only above a certain pine density. Above this threshold, fire resulted in increased pine dominance at the plot level, however below this threshold establishment rates did not change. We used a spatially explicit invasion simulation model modified to include fire to explore the implications of these complex interactions between pine invasions and fire. We asked if fire promoted P. contorta invasion across a Patagonian steppe site and if this depended on the age of the invasion when it burned. Our simulations indicated that, although fire was not necessary to initiate invasion, fire in communities where pine invasions were at least 10 years old resulted in increased spatial extent and maximum invasion density compared to unburned simulations. Fire through younger invasions did not alter the progression of the invasion compared to unburned simulations. Pine invasions should be managed before they reach an advanced stage where positive feedbacks between fire and pine invasion could lead to dramatic increases in invasion rate.

Unraveling patterns and processes of diversification in the South Andean-Patagonian Nassauvia subgenus Strongyloma (Asteraceae, Nassauvieae)

Congruence among different sources of data is highly desirable in phylogenetic analyses. However, plastid and nuclear DNA may record different evolutionary processes such that incongruence among results from these sources can help unravel complex evolutionary histories. That is the case of Nassauvia subgenus Strongyloma (Asteraceae), a taxon with five putative species distributed in the southern Andes and Patagonian steppe. Morphometric and phylogeographic information cast doubt on the integrity of its species, and previous molecular data even questioned the monophyly of the subgenus. We tested those questions using plastid and nuclear DNA sequences by the application of different methods such as phylogenetic trees, networks, a test of genealogical sorting, an analysis of population structure, calibration of the trees, and hybridization test, assembling non-synchronous incongruent results at subgenus and species levels in a single reconstruction. The integration of our molecular analyses and previous taxonomic, morphological, and molecular studies support subgenus Strongyloma as a monophyletic group. However, the topology of the nuclear trees and the evidence of polyploids within subgenus Nassauvia, suggest a hypothetical origin and initial radiation of Nassauvia related to an ancient hybridization event that occurred around 17–6.3 Myr ago near the Andes in west-central Patagonia. Plastid data suggest a recent diversification within subgenus Strongyloma, at most 9.8 Myr ago, towards the Patagonian steppe east of the Andes. These processes cause phylogenies to deviate from the species tree since each putative species lack exclusive ancestry. The non-monophyly of its species using both plastid and nuclear data is caused mainly by incomplete lineage sorting occurred since the Miocene. The final uplift of the Andes and Pliocene-Pleistocene glacial-interglacial and its consequences on the landscape and climate structured the genetic composition of this group of plants in the Patagonian steppe. The molecular data presented here agree with previous morphological studies, in that the five putative species typically accepted in this subgenus are not independent taxa. This study emphasizes that adding more than one sequence per species, not combining data with dissimilar inheritance patterns without first performed incongruence tests, exploring data through different methodologies, considering the timing of events, and searching for the causes of poorly resolved and/or incongruent phylogenies help to reveal complex biological underlying processes, which might otherwise remain hidden.