Showing papers by "National University of Comahue published in 2008"
TL;DR: It is reported that agriculture has become more pollinator dependent because of a disproportionate increase in the area cultivated with pollinator-dependent crops, thus not supporting the view that pollinator shortages are affecting crop yield at the global scale.
517 citations
TL;DR: Connectivity among native species declined in highly invaded webs, and links were transferred from generalist native species to super-generalist alien species during invasion, which can leave many native species subject to novel ecological and evolutionary dynamics.
Abstract: Plant–animal mutualisms are characterized by weak or asymmetric mutual dependences between interacting species, a feature that could increase community stability. If invasive species integrate into mutualistic webs, they may alter web structure, with consequences for species persistence. However, the effect of alien mutualists on the architecture of plant–pollinator webs remains largely unexplored. We analyzed the extent of mutual dependency between interacting species, as a measure of mutualism strength, and the connectivity of 10 paired plant–pollinator webs, eight from forests of the southern Andes and two from oceanic islands, with different incidences of alien species. Highly invaded webs exhibited weaker mutualism than less-invaded webs. This potential increase in network stability was the result of a disproportionate increase in the importance and participation of alien species in the most asymmetric interactions. The integration of alien mutualists did not alter overall network connectivity, but links were transferred from generalist native species to super-generalist alien species during invasion. Therefore, connectivity among native species declined in highly invaded webs. These modifications in the structure of pollination webs, due to dominance of alien mutualists, can leave many native species subject to novel ecological and evolutionary dynamics.
416 citations
TL;DR: Evidence is analyzed for the claim that IPT is an evolutionary force promoting character displacement in habitat affinity, flowering times, and floral morphology, and for impacts of alien plant species on native species' reproduction.
Abstract: Interspecific pollen transfer (IPT) is one of the mechanisms underlying potential competition among plants for pollinators, and it refers to movement of pollen between different plant species by pollinators that visit their flowers simultaneously. Two components of IPT, related to each other, are distinguished: (a) heterospecific pollen deposition (HPD) on conspecific stigmas, which may interfere with fertilization by conspecific pollen; and (b) conspecific pollen loss (CPL) on heterospecific flowers, which may reduce the amount of pollen transferred between conspecific flowers. Thus, IPT may lead to reciprocal losses for male and female functions of the plant, with potentially important ecological and evolutionary consequences. In this review, we explore the magnitude and prevalence of IPT, examining documented mechanisms and evaluating such potential ecological and evolutionary consequences. We compiled existing evidence of interspecific pollinator sharing and interspecific pollinator switching between ...
387 citations
TL;DR: Elk movements were characterized by a complex interplay between attraction to preferred habitat types and memory of previous movements across the home-range, suggesting that multiphasic structure is fundamental to the movement patterns of elk at all temporal and spatial scales tested.
Abstract: Recent theory suggests that animals should switch facultatively among canonical movement modes as a complex function of internal state, landscape characteristics, motion capacity, and navigational capacity. We tested the generality of this paradigm for free-ranging elk (Cervus elaphus) over 5 orders of magnitude in time (minutes to years) and space (meters to 100 km). At the coarsest spatiotemporal scale, elk shifted from a dispersive to a home-ranging phase over the course of 1-3 years after introduction into a novel environment. At intermediate spatiotemporal scales, elk continued to alternate between movement modes. During the dispersive phase, elk alternated between encamped and exploratory modes, possibly linked to changes in motivational goals from foraging to social bonding. During the home-ranging phase, elk movements were characterized by a complex interplay between attraction to preferred habitat types and memory of previous movements across the home-range. At the finest temporal and spatial scale, elk used area-restricted search while browsing, interspersed with less sinuous paths when not browsing. Encountering a patch of high-quality food plants triggered the switch from one mode to the next, creating biphasic movement dynamics that were reinforced by local resource heterogeneity. These patterns suggest that multiphasic structure is fundamental to the movement patterns of elk at all temporal and spatial scales tested.
317 citations
TL;DR: In this article, the adsorption of tetracycline (TC) on a Patagonian montmorillonite is studied as a function of pH, ionic strength and TC concentration by using X-ray diffraction, UV-Visible spectroscopy, ATR-FTIR spectrographs, batch experiments and adsorsorption modeling.
282 citations
TL;DR: The authors' model and field data show an interaction between plant spatial pattern and bird foraging, which results in neighbourhood-specific dispersal and rates of fruit removal, and as fruiting plants become aggregated, inequalities in fruit-removal rates increase and seed dispersal distance decreases.
Abstract: Summary 1. Frugivores disperse the seeds of the majority of woody plant species world-wide. Thus, insights on how frugivores influence the dispersal of plants and the variability of this process are crucial for understanding plant population dynamics in a rapidly changing world. 2. We used a spatially explicit, stochastic, individual-based model that simulates fruit-removal and seed dispersal by birds to assess bird density, landscape and neighbourhood effects on the inequalities of within-population fruit-removal rates and seed dispersal. We also compared model predictions with spatially-explicit field data. 3. In our simulations, bird density had a strong effect on the distribution of fruit-removal rates creating large inequalities among plants. Also, for equal bird densities, inequalities increased with the landscape level aggregation of plants. 4. Fruit removal increased with increasing plant neighbourhood density although there was a tendency to decline at the highest densities. Neighbourhood density also changed average dispersal distances, but with shorter distances at higher densities. Plants with few neighbours not only had longer distance dispersal but also a larger variance in seed rain across distances than plants with ten or more neighbours. These relationships between neighbourhood density and fruit removal and dispersal distance were scale-dependent with a peak in correlations at 150-m radius. 5. Similar to model predictions, field data shows an inverse relationship between dispersal distances (inferred from bird movements) and fruiting neighbourhood density. Also, fruit-removal rates observed in the field show large numbers of plants receiving little or zero fruit-removal. Fruitremoval rate distributions were statistically indistinguishable between the simulation and field data. But, distributions were strikingly different from two alternative models that lacked spatial effects. 6. Synthesis . Our model and field data show that as fruiting plants become aggregated, inequalities in fruit-removal rates increase and seed dispersal distance decreases. Both of these processes could help create and maintain plant aggregation and affect genetic structuring. The model also predicts that small-scale neighbourhood effects can be controlled by large-scale processes such as overall frugivore abundance and landscape-level plant aggregation. Most importantly, both simulations and field data shows an interaction between plant spatial pattern and bird foraging, which results in neighbourhood-specific dispersal and rates of fruit removal.
185 citations
TL;DR: The demographic timelines obtained for the two species illustrate the continent‐wide response of aquatic life in Patagonia to climate change during the Pleistocene, but also show how differing ecological traits and distributions led to distinctive responses.
Abstract: Changes in lake and stream habitats during the growth and retreat of Pleistocene glaciers repeatedly altered the spatial distributions and population sizes of the aquatic fauna of the southern Andes. Here, we use variation in mtDNA control region sequences to infer the temporal dynamics of two species of southern Andean fish during the past few million years. At least five important climate events were associated with major demographic changes: (i) the widespread glaciations of the mid-Pliocene (c. 3.5 Ma); (ii) the largest Patagonian glaciation (1.1 Ma); (iii) the coldest Pleistocene glaciation as indicated by stacked marine delta(18)O (c. 0.7 Ma); (iv) the last southern Patagonian glaciation to reach the Atlantic coast (180 ka); and (v) the last glacial maximum (LGM, 23-25,000 years ago). The colder-water inhabitant, Galaxias platei, underwent a strong bottleneck during the LGM and its haplotype diversity coalesces c. 0.7 Ma. In contrast, the more warm-adapted and widely distributed Percichthys trucha showed continuous growth through the last two glacial cycles but went through an important bottleneck c. 180,000 years ago, at which time populations east of the Andes may have been eliminated. Haplotype diversity of the most divergent P. trucha populations, found west of the Andes, coalesces c. 3.2 Ma. The demographic timelines obtained for the two species thus illustrate the continent-wide response of aquatic life in Patagonia to climate change during the Pleistocene, but also show how differing ecological traits and distributions led to distinctive responses.
158 citations
TL;DR: In this article, the authors analyzed the birds in the western mountains of the New World to examine the twofold effect of topography on species richness patterns, using two grains at the intercontinental extent and within temperate and tropical latitudes.
Abstract: Although topographic complexity is often associated with high bird diversity at broad geographic scales, little is known about the relative contributions of geomorphologic heterogeneity and altitudinal climatic gradients found in mountains. We analysed the birds in the western mountains of the New World to examine the two-fold effect of topography on species richness patterns, using two grains at the intercontinental extent and within temperate and tropical latitudes. Birds were also classified as montane or lowland, based on their overall distributions in the hemisphere. We estimated range in temperature within each cell and the standard deviation in elevation (topographic roughness) based on all pixels within each cell. We used path analysis to test for the independent effects of topographic roughness and temperature range on species richness while controlling for the collinearity between topographic variables. At the intercontinental extent, actual evapotranspiration (AET) was the primary driver of species richness patterns of all species taken together and of lowland species considered separately. In contrast, within-cell temperature gradients strongly influenced the richness of montane species. Regional partitioning of the data also suggested that range in temperature either by itself or acting in combination with AET had the strongest ‘‘effect’’ on montane bird species richness everywhere. Topographic roughness had weaker ‘‘effects’’ on richness variation throughout, although its positive relationship with richness increased slightly in the tropics. We conclude that bird diversity gradients in mountains primarily reflect local climatic gradients. Widespread (lowland) species and narrow-ranged (montane) species respond similarly to changes in the environment, differing only in that the richness of lowland species correlates better with broad-scale climatic effects (AET), whereas mesoscale climatic variation accounts for richness patterns of montane species. Thus, latitudinal and altitudinal gradients in species richness can be explained through similar climatic-based processes, as has long been argued.
127 citations
TL;DR: This analysis examines how a massive mortality event triggered by the 1998–1999 drought affected adult and sapling mortality and recruitment in a mixed Nothofagus dombeyi and Austrocedrus chilensis forests of northern Patagonia, and assessed changes in forest composition, microenvironments, and seedling density and survival of both species.
Abstract: Severe droughts have the potential of inducing transient shifts in forest canopy composition by altering species-specific adult tree mortality patterns. However, permanent vegetation change will occur only if tree recruitment patterns are also affected. Here, we analyze how a massive mortality event triggered by the 1998–1999 drought affected adult and sapling mortality and recruitment in a mixed Nothofagus dombeyi (Mirb.) Blume – Austrocedrus chilensis (D. Don) Flor. et Boult. forests of northern Patagonia. Comparing drought-induced and tree-fall gaps, we assessed changes in forest composition, microenvironments, and seedling density and survival of both species. Drought-kill disturbance shifted species composition of both canopy and sapling cohorts in favour of A. chilensis. Drought gaps were characterized by a shadier and more xeric environment, affecting the recruitment pattern of N. dombeyi seedlings. The seedling cohort was composed mostly of A. chilensis, and its survival was always higher than tha...
125 citations
TL;DR: It is suggested that plantations with more open canopy could favor biodiversity by increasing individual abundance and species richness of all three assemblages, supporting the view that the least vagile assemblage are most affected by habitat replacement.
114 citations
TL;DR: A new Late Cretaceous titanosaur sauropod from the Bauru Basin of Brazil, Uberabatitan ribeiroi gen. et al. as discussed by the authors, represented by at least three specimens, is described.
Abstract: A new Late Cretaceous titanosaur sauropod from the Bauru Basin of Brazil, Uberabatitan ribeiroi gen. et sp. nov., represented by at least three specimens, is described. The material comes from a level of coarse sandstone within the Serra da Galga sequence in Uberaba County, Minas Gerais State. The fossiliferous strata belong to the Marilia Formation (Serra da Galga Member), Bauru Group, considered to be Maastrichtian in age. The fossils occur in the uppermost levels of the above-mentioned unit; thus, Uberabatitan ribeiroi is the youngest titanosaur to have been recorded from the Bauru Basin. The autapomorphies that support the new species are: (1) anterior and mid-cervicals with postzygodiapophyseal lamina (podl) segmented in zygapophyseal and diapophyseal laminae, of which the first extends rostrodorsally over the second; (2) mid-dorsals with a robust lateral lamina formed mainly by a diapophyseal lamina (probably homologous to the postzygodiapophyseal lamina), and, to a lesser extent, by a relic of the spinodiapophyseal lamina (spdl); (3) mid (and probably posterior) dorsals with accessory neural laminae, which are lateral to the prespinal lamina, and probably homologous to the spinoprezygapophyseal laminae (sprl); (4) mid-caudal centra with deeply excavated lateral faces; (5) pubis very thick and robust, with a very stout longitudinal crest on its external (ventral) face; and (6) proximal end of the tibia with a prominent lateral protuberance, which articulates with an equally prominent medial knob of the fibula. The titanosaurian assemblage at Uberaba includes, apart from U. ribeiroi, well-preserved specimens assigned to species of uncertain affinities (Trigonosaurus pricei and Baurutitan britoi), as well as a few vertebrae assigned to aeolosaurines.
TL;DR: Investigating the cultural transmission of two types of traditional plant knowledge in two communities of North-western Patagonia, Argentina found that wild plant use and horticultural knowledge continue to be learned during adulthood, particularly among elder adults and youngsters.
Abstract: Background
In the present study we have investigated the cultural transmission of two types of traditional plant knowledge in two communities of North-western Patagonia, Argentina. In the Pilcaniyeu community, we studied the transmission of traditional knowledge related to horticultural practices in home-gardens, greenhouses and gardens; while in the community of Cuyin Manzano, we studied wild plant gathering customs.
TL;DR: Results show that grazing influenced nutrient cycling by modifying litter breakdown within species as well as the soil environment for decomposition, and indicate that grazing effects on decomposition are likely to involve aerial litter pools rather than the more recalcitrant root compartment.
Abstract: Large herbivores may alter carbon and nutrient cycling in soil by changing above- and below-ground litter decomposition dynamics. Grazing effects may reflect changes in plant allocation patterns, and thus litter quality, or the site conditions for decomposition, but the relative roles of these broad mechanisms have rarely been tested. We examined plant and soil mediated effects of grazing history on litter mass loss and nutrient release in two grazing-tolerant grasses, Lolium multiflorum and Paspalum dilatatum, in a humid pampa grassland, Argentina. Shoot and root litters produced in a common garden by conspecific plants collected from grazed and ungrazed sites were incubated under both grazing conditions. We found that grazing history effects on litter decomposition were stronger for shoot than for root material. Root mass loss was neither affected by litter origin nor incubation site, although roots from the grazed origin immobilised more nutrients. Plants from the grazed site produced shoots with higher cell soluble contents and lower lignin:N ratios. Grazing effects mediated by shoot litter origin depended on the species, and were less apparent than incubation site effects. Lolium shoots from the grazed site decomposed and released nutrients faster, whereas Paspalum shoots from the grazed site retained more nutrient than their respective counterparts from the ungrazed site. Such divergent, species-specific dynamics did not translate into consistent differences in soil mineral N beneath decomposing litters. Indeed, shoot mass loss and nutrient release were generally faster in the grazed grassland, where soil N availability was higher. Our results show that grazing influenced nutrient cycling by modifying litter breakdown within species as well as the soil environment for decomposition. They also indicate that grazing effects on decomposition are likely to involve aerial litter pools rather than the more recalcitrant root compartment.
TL;DR: In the Nothofagus forest region of southern Argentina and Chile in the late 1990s and early 2000s, the risk of wildfire ignition and spread has been exacerbated by increases in lightning associated with higher temperatures, increased ignitions associated with exurban development, and conversion of less flammable native vegetation to more flammably plantations of exotic conifers as discussed by the authors.
Abstract: The present synthesis addresses key questions about several extreme fire events that occurred in the Nothofagus forest region of southern Argentina and Chile in the late 1990s and early 2000s: (1) are there historical precedents for the extent and severity of these recent wildfires? (2) To what extent can large, severe fires be attributed to influences from modern humans, either indirectly through land-use practices or directly through ignition? (3) What are the relationships of these fire events to interannual climatic variability and trends? (4) What are the medium-term ecological consequences of these fire events, particularly in terms of the resiliency of the burned ecosystems? Historic fire regimes vary greatly across the different ecosystem types in the southern Andean region, and the tree-ring record shows that before the 20th century, large severe fires also played a significant ecological role in shaping even the wettest forests. Recent severe droughts at an annual time scale have been facilitated by a trend towards higher temperatures since the mid-1970s. In large parts of the region, the risk of wildfire ignition and spread has been exacerbated by increases in lightning associated with higher temperatures, increased ignitions associated with exurban development, and conversion of less flammable native vegetation to more flammable plantations of exotic conifers.
TL;DR: A significant decline in the relative abundances of salmonids and an increase of P. trucha are found from twenty years back up to the present: basic concepts needed not only in future research but also in management design for Patagonian fish populations.
Abstract: The interaction between native fishes and salmonids introduced in Patagonia at the beginning of the 20th Century, developed at the same time as the environmental change. The phenomenon of global warming has led to the formulation of predictions in relation to changes in the distribution of species, in the latitudinal dimension, both at intralacustrine, or small streams levels. The aim of the present work includes three main objectives: a) to compose a general and updated picture of the latitudinal distribution range of native and alien fishes, b) to analyze the historical changes in the relative abundance of Percichthys trucha, Odontesthes sp., and salmonids in lakes and reservoirs, and c) to relate the diversity and relative abundance of native and salmonid fishes to the environmental variables of lakes and reservoirs. We analysed previous records and an ensemble of data about new locations along the northern border of the Patagonian Province. We compared current data about the relative abundance of native fishes and salmonids in lakes and reservoirs, with previous databases (1984–1987). All samplings considered were performed during spring-summer surveys and include relative abundance, as proportions of salmonids, P. trucha, and Odontesthes sp. For the first time, we found changes in fish assemblages from twenty years back up to the present: a significant decline in the relative abundances of salmonids and an increase of P. trucha. We studied the association between the diversity and relative abundance of native and salmonid fishes and the environmental variables of lakes and reservoirs using Canonical Correspondence Analysis. Relative abundance showed mainly geographical cues and the diversity relied largely on morphometric characteristics. Relative abundance and diversity seem to have a common point in the lake area, included into the PAR concept. Native abundance and alien diversity were negatively related with latitude. Greater native diversity was observed in lakes with high PAR compared with salmonids. Historical changes such as southward dispersion, relative abundance changes, and geographical patterns for relative abundance and diversity are basic concepts needed not only in future research but also in management design for Patagonian fish populations.
TL;DR: It is suggested that native seed predators can be an important component of biological resistance to plant invasion, substantially reducing the chances of exotic seed establishment in Patagonia.
Abstract: Interactions between exotic plants and animals can play a major role in determining success or failure of plant introductions. Seed predation has been seen as important in explaining biotic resistance to plant invasion, but this hypothesis has rarely been tested. We studied seed predation on exotic forest plants on an island in Patagonia, Argentina where 43 pine species, including 60% of the world’s known invasive Pinaceae, were introduced ca. 80 years ago, but where exotics attain relatively high densities only near the original plantings. To test if seed predation limits exotic conifer establishment in this area, we compared seed predation in areas close to plantations (colonized by exotics) and far from them (not invaded). Seeds of exotics were preferred over seeds of native species, possibly because exotic seeds are bigger. Predation was more intense in areas far from plantations than in areas close to them, substantially reducing the chances of exotic seed establishment. Using automatic cameras, we found that both rodents and birds preyed on exotic seeds. This study suggests that native seed predators can be an important component of biological resistance to plant invasion.
TL;DR: In this paper, the effect of previous blanching and calcium impregnation at atmospheric pressure (AI) or in vacuum (VI) on the rate of moisture movement during the first falling rate period of air drying of apples at 60°C was studied.
TL;DR: Comparisons with historical records of Bombus dahlbomii abundances prior to Bombus ruderatus’ invasion suggest that the overall pollination intensity of A. aurea might in fact have risen as a consequence of this invasion, as well as related pollinator traits that might account for potential differences in pollinator efficiency.
Abstract: Biological invasions might constitute a major threat to mutualisms. Introduced pollinators might competitively displace their native counterparts, which in turn affects the pollination of native plants, if native and alien visitors differ in pollinator effectiveness. Since its invasion in 1994 into south-west Argentina, the introduced European bumblebee Bombus ruderatus has continuously increased in abundance, along with a simultaneous decrease in the abundance of the native Bombus dahlbomii. The latter is the only native bumblebee species of the temperate forests of southern South America, and the main pollinator of the endemic herb Alstroemeria aurea. In order to evaluate the impact of the ongoing displacement of the native by the alien bumblebee, we compared the pollinator effectiveness (i.e., the combination of pollinator efficiency per visit and visitation frequency) between both bumblebee species, as well as related pollinator traits that might account for potential differences in pollinator efficiency. Native Bombus dahlbomii, which has a larger body and spent more time per flower, was the more efficient pollinator compared to Bombus ruderatus, both in terms of quantity and quality of pollen deposited per visit. However, Bombus ruderatus was a much more frequent flower visitor than Bombus dahlbomii. As a consequence, Bombus ruderatus is nowadays a more effective pollinator of A. aurea than its native congener. Despite the lack of evidence of an increase in seed set at the population level, comparisons with historical records of Bombus dahlbomii abundances prior to Bombus ruderatus' invasion suggest that the overall pollination intensity of A. aurea might in fact have risen as a consequence of this invasion. Field experiments like these, that incorporate the natural variation in abundance of native and alien species, are powerful means to demonstrate that the consequences of invasions are more complex than previous manipulated and controlled experiments have suggested.
TL;DR: Support for the fencing of recently burned Nothofagus and Austrocedrus forests in the national parks for periods long enough to allow the dominant tree species to grow to heights at which they are no longer severely inhibited by cattle browsing is provided.
TL;DR: This is the first comprehensive phylogenetic study of Phyllactinia and other endo-parasitic genera of the Erysiphales and revealed that host range expansion at higher taxonomic levels (higher than family level) is independent of the phylogeny of plants.
TL;DR: Andean-Patagonian forests are especially interesting for the study of N and P limitation because they receive minimal atmospheric pollution, have little influence of vascular N-fixing species, and grow on volcanic soils that retain P.
TL;DR: Plants can gain access to and benefit from the nutrient content of ant RD, supporting the hypotheses that enhanced resource availability promotes exotic plant performance that could increase the likelihood of biological invasions.
Abstract: Understanding the mechanisms that promote the invasion of natural protected areas by exotic plants is a central concern for ecology. We demonstrated that nests of the leaf-cutting ant, Acromyrmex l...
TL;DR: The RAC yeast community resembles that of acidic aquatic environments resulting from anthropic activities such as the São Domingos mines in Portugal and the Rio Tinto in Spain, respectively, and the isolated yeast species were organized into different grades of adaptation to the RAC aquatic system.
TL;DR: The existence of negative autocorrelation in seed production between year 0 and year -2 at the individual tree level suggests the presence of 'switching' or internal resource allocation, thus discarding the resource matching hypothesis.
Abstract: Masting, the intermittent and synchronous production of large seed crops, may result from either of two major processes: resource matching and economy of scale. Components of cone production in Araucaria araucana were partitioned among populations and trees to ascertain the existence of masting and the processes involved. Cone production data from seven populations were obtained during a 9-year period and seed gathering data were available for an 18-year time series from six sites in an area of more than 7600 km 2 . Araucaria araucana showed environmentally triggered, intermittent, moderately fluctuating, and highly regionally synchronous reproduction.The mean pairwise correlations of cones production among populations and seed gathering sites were 0.89 and 0.74, respectively, suggesting synchrony in reproduction. Among trees we observed a mean correlation of 0.74 with values ranging from 0.66 to 0.81 for the analysed populations.The existence of negative autocorrelation in seed production between year 0 and year -2 at the individual tree level suggests the presence of 'switching' or internal resource allocation, thus discarding the Resource Matching hypothesis. Mean coefficient of variation (CVp) among populations was moderate (0.95) and similar to the modal CVp values reported in the published reports. Mean CVi among individual trees was 1.16, suggesting a large number of equally and synchronously fluctuating trees, rather than a few largely fluctuating individuals. These results suggest that pollination efficiency and/or predator satiation hypotheses could be responsible for the masting cycles in this conifer. Ancillary data about limitation of airborne pollen dispersion and temporal variation in the amount of seeds per cone and about seed predator satiation, also support both proposed mechanisms.
TL;DR: The results suggest that diet, the ability to be active over a broad thermal range, and a longer activity season can counteract the effect of body temperature on the timing and allocation of energy to growth, maturation and reproduction.
TL;DR: It is hypothesize that the low rates of invasion currently observed can result at least partly from high densities of exotic deer, which, despite their preference for natives, can prevent establishment of both native and exotic trees.
Abstract: How interactions between exotic species affect invasion impact is a fundamental issue on both theoretical and applied grounds. Exotics can facilitate establishment and invasion of other exotics (invasional meltdown) or they can restrict them by re-establishing natural population control (as predicted by the enemy- release hypothesis). We studied forest invasion on an Argentinean island where 43 species of Pinaceae, including 60% of the world's recorded invasive Pinaceae, were introduced c. 1920 but where few species are colonizing pristine areas. In this area two species of Palearctic deer, natural enemies of most Pinaceae, were introduced 80 years ago. Expecting deer to help to control the exotics, we conducted a cafeteria experiment to assess deer preferences among the two dominant native species (a conifer, Austrocedrus chilensis, and a broadleaf, Nothofagus dombeyi) and two widely introduced exotic tree species (Pseudotsuga menziesii and Pinus ponderosa). Deer browsed much more intensively on native species than on exotic conifers, in terms of number of individuals attacked and degree of browsing. Deer preference for natives could potentially facilitate invasion by exotic pines. However, we hypothesize that the low rates of invasion currently observed can result at least partly from high densities of exotic deer, which, despite their preference for natives, can prevent establishment of both native and exotic trees. Other factors, not mutually exclusive, could produce the observed pattern. Our results underscore the difficulty of predicting how one introduced species will effect impact of another one.
TL;DR: The increase in the antioxidant metabolism observed in the posthatching phase of development of B. arenarum embryo constitutes a defense against natural and human‐generated pro‐oxidants present in the aquatic environment, and is concluded that oxidative stress is overcome by the antioxidant defenses.
Abstract: Amphibians may be critically challenged by aquatic contaminants during their embryonic development. Many classes of compounds, including organophosphorus pesticides, are able to cause oxidative stress that affects the delicate cellular redox balance regulating tissue modeling. We determined the progression of antioxidant defenses during the embryonic development of the South American common toad, Bufo arenarum. Superoxide dismutase (SOD) and catalase (CAT) activities were high in the unfertilized eggs, and remained constant during the first stages of development. SOD showed a significant increase when the gills were completely active and opercular folds began to form. Reductase (GR) activity was low in the oocytes and increased significantly when gills and mouth were entirely developed and the embryos presented a higher exposure to pro-oxidant conditions suggesting an environmental control. Reduced glutathione (GSH) content was also initially low, and rose continuously pointing out an increasing participation of GSH-related enzymes in the control of oxidative stress. GSH peroxidases and GSH-S-transferases showed relatively high and constant activities, probably related to lipid peroxide control. B. arenarum embryos have plenty of yolk platelets containing lipids, which provide the energy and are actively transferred to the newly synthesized membranes during the early embryonic development. Exposure to the pro-oxidant pesticide malathion during 48 h did not significantly affect the activity of antioxidant enzymes in early embryos, but decreased the activities of CAT, GR, and the pool of GSH in larvae. Previous work indicated that lipid peroxide levels were kept low in malathion-exposed larvae, thus we conclude that oxidative stress is overcome by the antioxidant defenses. The increase in the antioxidant metabolism observed in the posthatching phase of development of B. arenarum embryo, thus constitutes a defense against natural and human-generated pro-oxidants present in the aquatic environment.
TL;DR: Pollen limitation of the yield among animal-pollinated crops may be common and indicative not only of pollinator scarcity, but also of poor pollination quality, whereby pollinator efficiency, rather than just abundance, can play a broader role than previously appreciated.
Abstract: A decline in pollination function has been linked to agriculture expansion and intensification. In northwest Argentina, pollinator visits to grapefruit, a self-compatible but pollinator-dependent crop, decline by approximately 50% at 1 km from forest edges. We evaluated whether this decrease in visitation also reduces the pollination service in this crop. We analysed the quantity and quality of pollen deposited on stigmas, and associated limitation of fruit production at increasing distances (edge: 10, 100, 500 and 1000 m) from the remnants of Yungas forest. We also examined the quantitative and qualitative efficiency of honeybees as pollen vectors. Pollen receipt and pollen tubes in styles decreased with increasing distance from forest edge; however, this decline did not affect fruit production. Supplementation of natural pollen with self- and cross-pollen revealed that both pollen quantity and quality limited fruit production. Despite pollen limitation, honeybees cannot raise fruit production because they often do not deposit sufficient high-quality pollen per visit to elicit fruit development. However, declines in visitation frequency well below seven visits during a flower’s lifespan could decrease production beyond current yields. In this context, the preservation of forest remnants, which act as pollinator sources, could contribute to resilience in crop production. Like wild plants, pollen limitation of the yield among animal-pollinated crops may be common and indicative not only of pollinator scarcity, but also of poor pollination quality, whereby pollinator efficiency, rather than just abundance, can play a broader role than previously appreciated.
TL;DR: In this article, the degradability and nutrient release capacity of municipal organic waste (MOW) composts obtained with different management practices: shredding and/or mixing with wood shavings, cocomposting with biosolids, and vermic-composting.
Abstract: We studied the degradability and nutrient release capacity of municipal organic waste (MOW) composts obtained with different management practices: shredding and/or mixing with wood shavings, cocomposting with biosolids, and vermicomposting. As indicators of degradability and nutrient release capacity, we measured net N and C mineralization, extractable-P release, N retained in microbial biomass, and dehydrogenase activity in 16-week laboratory incubations, using soil amended at a rate of 40 g kg −1 . We also determined the extent to which these indicators were predicted from the chemical characteristics of the amendments. All products increased soil N and P availability, and the size and activity of soil microbial populations. Carbon and N mineralization, and extractable-P release were influenced by amendment chemical characteristics, especially organic matter, total N, total P, C to N ratio, extractable-P and water soluble C. Cocomposting MOW and biosolids is an important alternative for MOW management, because it was the most effective strategy at increasing product degradability and nutrient release capacity (highest net N and C mineralization, extractable-P release, and microbial biomass-N). Shredding MOW increased C mineralization, while the addition of wood shavings decreased net N mineralization, but generally did not affect C mineralization. Thus, these two practices should be used when these specific product characteristics wish to be achieved. Vermicomposting did not prove to be an efficient strategy when MOW was mixed with biosolids.
TL;DR: Low food quality may also impose a weaker antioxidant response on the organisms, a response of considerable ecological relevance in transparent Andean lakes which combine high UVR intensities with low seston P :C ratios.
Abstract: We experimentally tested the effect of food quality (phosphorus [P] : carbon [C] ratio) on the response of antioxidant enzymes to ultraviolet radiation (UVR) in Daphnia commutata fed with Chlamydomonas reinhardtii. Algal cultures were grown at different concentrations of phosphorus and light intensities, resulting in significant differences in the P :C ratios (mmol P[µmol C]−1; 6.05, 1.70, and 0.83). After 12 d of D. commutata growth under these three food quality treatments, we observed significant differences in individual biomass and protein content of Daphnia. Subsequently, we carried out an ultraviolet exposure experiment to determine if stoichiometric constraints imposed would limit enzymatic defenses against UVR oxidative stress. The UVR-exposure experiment consisted of a factorial design with three levels of food P :C (low, medium, and high) and two levels of UVR (exposed and protected). The activities of glutathione S-transferases (GST) and catalase (CAT), enzymes involved in protection and repair of damage caused by UVR, were determined. Enzyme activities in the animals exposed to or protected from UVR showed a direct relationship with food P :C ratio that fit exponential models. Although GST and CAT differed slightly in their response to UVR, both enzymes were significantly affected by food quality: In low P :C treatments, there was significantly lower enzyme activity in response to UVR for both enzymes. Low food quality (less P for biosynthesis) may also impose a weaker antioxidant response on the organisms, a response of considerable ecological relevance in transparent Andean lakes which combine high UVR intensities with low seston P :C ratios.