Showing papers by "National University of Comahue published in 2006"

Plant Reproductive Susceptibility to Habitat Fragmentation: Review and Synthesis Through a Meta-Analysis

Abstract: The loss and fragmentation of natural habitats by human activities are pervasive phenomena in terrestrial ecosystems across the Earth and the main driving forces behind current biodiversity loss. Animal-mediated pollination is a key process for the sexual reproduction of most extant flowering plants, and the one most consistently studied in the context of habitat fragmentation. By means of a meta-analysis we quantitatively reviewed the results from independent fragmentation studies throughout the last two decades, with the aim of testing whether pollination and reproduction of plant species may be differentially susceptible to habitat fragmentation depending on certain reproductive traits that typify the relationship with and the degree of dependence on their pollinators. We found an overall large and negative effect of fragmentation on pollination and on plant reproduction. The compatibility system of plants, which reflects the degree of dependence on pollinator mutualism, was the only reproductive trait that explained the differences among the species' effect sizes. Furthermore, a highly significant correlation between the effect sizes of fragmentation on pollination and reproductive success suggests that the most proximate cause of reproductive impairment in fragmented habitats may be pollination limitation. We discuss the conservation implications of these findings and give some suggestions for future research into this area.

Invasive mutualisms and the structure of plant–pollinator interactions in the temperate forests of north‐west Patagonia, Argentina

Abstract: Summary 1 Alien species may form plant–animal mutualistic complexes that contribute to their invasive potential. Using multivariate techniques, we examined the structure of a plant–pollinator web comprising both alien and native plants and flower visitors in the temperate forests of north-west Patagonia, Argentina. Our main objective was to assess whether plant species origin (alien or native) influences the composition of flower visitor assemblages. We also examined the influence of other potential confounding intrinsic factors such as flower symmetry and colour, and extrinsic factors such as flowering time, site and habitat disturbance. 2 Flowers of alien and native plant species were visited by a similar number of species and proportion of insects from different orders, but the composition of the assemblages of flower-visiting species differed between alien and native plants. 3 The influence of plant species origin on the composition of flower visitor assemblages persisted after accounting for other significant factors such as flowering time, bearing red corollas, and habitat disturbance. This influence was at least in part determined by the fact that alien flower visitors were more closely associated with alien plants than with native plants. The main native flower visitors were, on average, equally associated with native and alien plant species. 4 In spite of representing a minor fraction of total species richness (3.6% of all species), alien flower visitors accounted for > 20% of all individuals recorded on flowers. Thus, their high abundance could have a significant impact in terms of pollination. 5 The mutualistic web of alien plants and flower-visiting insects is well integrated into the overall community-wide pollination web. However, in addition to their use of the native biota, invasive plants and flower visitors may benefit from differential interactions with their alien partners. The existence of these invader complexes could contribute to the spread of aliens into novel environments.

Phylogeography of the Percichthyidae (Pisces) in Patagonia: roles of orogeny, glaciation, and volcanism

Abstract: We used molecular evidence to examine the roles that vicariance mechanisms (mountainbuilding and drainage changes during the Pleistocene) have played in producing phylogeographical structure within and among South American fish species of the temperate perch family Percichthyidae. The percichthyids include two South American genera, Percichthys and Percilia , each containing several species, all of which are endemic to southern Argentina and Chile (Patagonia). Maximum-likelihood phylogenies constructed using mitochondrial DNA (mtDNA) control region haplotypes and nuclear GnRH3-2 intron allele sequences support the current taxonomy at the genus level (both Percichthys and Percilia form strongly supported, monophyletic clades) but indicate that species-level designations need revision. Phylogeographical patterns at the mtDNA support the hypothesis that the Andes have been a major barrier to gene flow. Most species diversity occurs in watersheds to the west of the Andes, together with some ancient divergences among conspecific populations. In contrast, only one species ( Percichthys trucha ) is found east of the Andes, and little to no phylogeographical structure occurs among populations in this region. Mismatch analyses of mtDNA sequences suggest that eastern populations last went through a major bottleneck c . 188 000 BP , a date consistent with the onset of the penultimate and largest Pleistocene glaciation in Patagonia. We suggest that eastern populations have undergone repeated founder-flush events as a consequence of glacial cycles, and that the shallow phylogeny is due to mixing during recolonization periods. The area of greater diversity west of the Andes lies outside the northern limit of the glaciers. mtDNA mismatch analysis of the genus Percilia which is restricted to this area suggests a long-established population at equilibrium. We conclude that patterns of genetic diversity in these South American genera have been primarily influenced by barriers to gene flow (Andean orogeny, and to a lesser extent, isolation in river drainages), and by glacial cycles, which have resulted in population contraction, re-arrangement of some watersheds, and the temporary breakdown of dispersal barriers among eastern river systems.

UV radiation as a potential driving force for zooplankton community structure in patagonian lakes

Abstract: This article explores the potential role of UV radiation (UVR) as an influence on zooplankton communities. In the first section we provide a general overview of UVR effects on freshwater zooplankton, with an emphasis on Argentine and Chilean environments. In the second section we present the results of a survey involving 53 temperate lakes across a gradient of UVR exposure to determine patterns of species richness and specific diversity. These community characteristics decreased at high potential UVR exposure (i.e. high mean water column irradiance or low lake optical density). A threshold value of mean water column irradiance of approximately 10% of the surface level seems to limit both richness and diversity to minimum values. On the basis of the collected evidence it is not possible to definitely conclude that UVR rather than another covarying factor is responsible for the decrease in specific diversity observed at the lowest end of lake optical depth. However, lakes with values above the previous threshold are likely to exhibit highly depauperate zooplankton communities regardless of the mechanism. As a cautionary note we suggest that changes in the optical characteristics (i.e. changes due to atmospheric conditions, precipitation patterns or vertical displacement of the tree line) may result in sudden shifts in zooplankton community structure.

Yeast Diversity in the Extreme Acidic Environments of the Iberian Pyrite Belt

Abstract: In the Iberian Pyrite Belt (IPB), acid rock drainage gives rise to aquatic habitats with low pH and high concentrations of heavy metals, a situation that causes important environmental problems. We investigated the occurrence and diversity of yeasts in two localities of the IPB: Sao Domingos (Portugal) and Rio Tinto (Spain). Yeast isolation was performed on conventional culture media (MYP), acidified (pH 3) media (MYP3), and on media prepared with water from the study sites (MYPw). The main goal of the study was to determine the structure of the yeast community; a combination of molecular methods was used for accurate species identifications. Our results showed that the largest fraction of the yeast community was recovered on MYPw rather than on MYP and MYP3. Twenty-seven yeast species were detected, 48% of which might represent undescribed taxa. Among these, an undescribed species of the genus Cryptococcus required low pH for growth, a property that has not been observed before in yeasts. The communities of S. Domingos and R. Tinto showed a considerable resemblance, and eight yeast species were simultaneously found in both localities. Taking into consideration the physicochemical parameters studied, we propose a hierarchic organization of the yeast community in terms of high-, intermediate-, or low-stress conditions of the environment. According to this ranking, the acidophile yeast Cryptococcus sp. 5 is considered the most tolerant species, followed by Cryptococcus sp. 3 and Lecytophora sp. Species occurring in situations of intermediate environmental stress were Candida fluviatilis, Rhodosporidium toruloides, Williopsis californica, and three unidentified yeasts belonging to Rhodotorula and Cryptococcus.

Reappraisal of an ankylosaurian dinosaur from the Upper Cretaceous of James Ross Island (Antarctica)

Abstract: The holotype of the upper Campanian ankylosaur Antarctopelta oliveroi n. gen., n. sp., from James Ross Island, Antarctica, is described. Diagnostic characters include short cervicals (centrum length about 70% of the centrum height), distal caudal vertebrae with transverse processes well developed (centrum width including the transverse processes exceeds 30% of the posterior articulation width) and dorsoventrally depressed, and the presence of smooth, sub-circular osteoderms, surrounded by a mosaic of smaller polygonal osteoderms with a rugose surface texture and tiny, button-like ossicles. While a number of features, such as relatively large teeth with respect to the mandible and the presence of an asymmetrical cingulum, suggest an affinity with the Nodosauridae, others such as the dorsoventrally depressed morphology of the distal caudal vertebrae and, especially, the presence of ossified tendons on their ventral side, characterize the Ankylosauridae. This uncertainty impedes evaluation of the paleobiogeographi cal significance of this new species of dinosaur. RESUME

Flowering phenologies of hummingbird plants from the temperate forest of southern South America: is there evidence of competitive displacement?

Abstract: Plant species sharing pollinators may compete through pollination. This type of competition may lead to overdispersed flowering phenologies. However, phenological segregation is difficult to detect in seasonal climates. We compared patterns of phenological overlap in assemblages of ornithophilous plants from three localities of the temperate forest of southern South America with those generated by four different null models. These species were all visited and presumably pollinated by a single species, the hummingbird Sephanoides sephaniodes, which makes this situation ideal to evaluate the role of pollination-mediated competition. For one site, we compiled data on flowering phenologies for three different years. Three models considered the flowering period of the whole assemblage of ornithophilous plants as the phenological window within which flowering phenologies were randomized, but made no further assumptions on how species should be distributed within that temporal frame. The fourth model assigned differential probabilities to different time intervals based on the flowering onset of non-ornithophilous plant species. Observed mean pairwise overlaps for all localities and years were well within the interval defined by the 2.5 and 97.5% percentiles of the randomized distribution of expected mean pairwise overlaps according to models 1–3. However, model 4 showed a consistent trend towards overdispersion of ornihophilous phenologies, which show a shift towards mid- to late-summer flowering. Thus, to the extent that the distribution of flowering of non-ornithophilous species reflects the constraints imposed by a highly seasonal climate, our results provide support to the proposal that pollinator sharing may cause evolutionary displacement or ecological sorting of flowering phenologies. Other factors, such as phylogenetic inertia, could also contribute to explain extant phenological patterns in the highly endemic ornithophilous flora of the temperate forest of southern South America.

Effects of position, understorey vegetation and coarse woody debris on tree regeneration in two environmentally contrasting forests of north-western Patagonia: a manipulative approach

Abstract: Aim To investigate the differential effects of position within gaps, coarse woody debris and understorey cover on tree seedling survival in canopy gaps in two old-growth Nothofagus pumilio (Poepp & Endl) Krasser forests and the response of this species to gaps in two forests located at opposite extremes of a steep rainfall gradient Location Nahuel Huapi National Park, at 41° S in north-western Patagonia, Argentina Methods In both study sites, seedlings were transplanted to experimental plots in gaps in three different positions, with two types of substrate (coarse woody debris or forest floor), and with and without removal of understorey vegetation Survival of seedlings was monitored during two growing seasons Soil moisture and direct solar radiation were measured once in mid-summer Seedling aerial biomass was estimated at the end of the experiment Results Mid-summer soil water potential was lowest in the centre of gaps, in plots where the understorey had been removed, and highest at the northern edges of gaps Direct incoming radiation was highest in gap centres and southern edges, and lowest at northern edges Seedling mortality was highest in gap centres, in both sites Coarse woody debris had a positive effect on seedling survival during summer in the mesic forest and during winter in the xeric forest The removal of understorey cover had negative effects in gap centres during summer Seedling final aerial biomass was positively affected by understorey removal and by soil substrate in both sites In the dry forest gaps, seedling growth was highest in northern edges, whereas it was highest in gap centres in the mesic forest Overall growth was positively related to survival in the xeric forest, and negatively related in the mesic forest Main conclusions Survival and growth were facilitated by the shade of gap-surrounding trees only in the xeric forest Understorey vegetation of both forests facilitated seedling survival in exposed microsites but competed with seedling growth Nurse logs were an important substrate for seedling establishment in both forests; however, causes of this pattern differed between forests Water availability positively controls seedling survival and growth in the xeric forest while in the mesic forest, survival and growth are differentially controlled by water and light availability, respectively These two contrasting old-growth forests, separated by a relatively short distance along a steep rainfall gradient, had different yet unexpected microenvironmental controls on N pumilio seedling survival and growth These results underscore the importance of defining microscale limiting factors of tree recruitment in the context of large-scale spatial variation in resources

Biomass and carotenoid pigment production by patagonian native yeasts

Abstract: New yeast isolates from unexplored Patagonian habitats were studied for the production of biomass and carotenoids as the first step towards the selection of hyper-producing strains and the design of a process optimization approach. Patagonian yeast isolates considered as potential biomass and carotenoid sources were studied using ammonium sulphate and urea as nitrogen sources in semi-synthetic medium (MMS), and agro-industrial byproducts (cane molasses, corn syrup, raw malt extract) as carbon sources. Maximum pigment production (300 μg g−1) was achieved by Rhodotorula mucilaginosa CRUB 0195 and by novel species Cryptococcus sp. CRUB 1046. β-carotene, torulene and torularhodin were the major carotenoids found.

Latitudinal and ecological correlates of morphological variation in Galaxias platei (Pisces, Galaxiidae) in Patagonia

Abstract: We examined the morphological variability (23 morphometric traits) among individual Galaxias platei ( N = 380) col- lected from 20 postglacial lakes in the southern Andes. The lakes were chosen to cover the latitudinal range of the species in Patagonia. Diet examined for a subset of these fish ( N = 261) collected during the summer months (Jan- uary through March), differed among river basins but there were no clear latitudinal trends in the consumption of any prey type. Diet may, however, have partially shaped morphology, as pelvic measures were negatively correlated with consumption of amphipods. Substantial differentiation among populations was observed, primarily in the shape and dimensions of the head, in caudal morphology and in fin length. Our results indicate that the morphology of G. platei varies with latitude, and may be related to risk of predation and diet. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 69-82.

Is the decline of birds and amphibians in a steppe lake of northern Patagonia a consequence of limnological changes following fish introduction

Abstract: 1 Laguna Blanca, in Laguna Blanca National Park, is a lake in Patagonia which has been designated as a Ramsar site since 1971 because of bird diversity and abundance and importance for nesting, particularly for the black neck swan, Cygnus melanocoryphus It is also valued for its populations of endemic amphibians, Atelognathus patagonicus and Atelognathus praebasalticus 2 Avian and amphibian populations have decreased dramatically in recent years Percichthys colhuapiensis, Percichthys trucha (Pisces, Percichthyidae), Salmo trutta and Oncorhynchus mykiss (Pisces, Salmonidae) were introduced into Laguna Blanca in 1965 Since 1986, no Atelognathus frogs have been found The abundance of swans and coots, which are strongly associated with macrophytes for nesting and feeding, has diminished drastically, whereas piscivorous birds have increased 3 The fishless condition of some neighbouring small lakes with abundant pond weeds, aquatic birds and endemic amphibians, was assessed in order to compare the physical and chemical characteristics and the quantitative composition of the benthos among lakes Fish presence at Laguna Blanca and its absence at El Burro, Antinir and Jabon lakes, were confirmed Compared with previous results, it seems that the abundance of Amphipoda (Hyalella), Copepoda and Cladocera at Laguna Blanca has decreased, while Acari has increased and Notostraca has disappeared Water transparency has diminished in Laguna Blanca and now is lower than that of fishless lakes 4 P colhuapiensis were captured only in Laguna Blanca, with the highest captures in the littoral zone The population shows rapid individual growth in the early years and an absence of fish older than 6 years The preponderance of benthos and the presence of macrophytes in the gut contents of adult P colhuapiensis appear to indicate that they are important consumers of these resources 5 This paper concludes that fish introduction in Laguna Blanca led to a complex trophic cascade effect (fish predation on tadpoles, fish competition for avian food, bottom disturbance, zooplankton reduction) producing deleterious effects on the amphibian and bird populations Copyright © 2006 John Wiley & Sons, Ltd

Effect of fire on ground beetles and ant assemblages along an environmental gradient in NW Patagonia: Does habitat type matter?

Abstract: The response of beetle and ant assemblages to fire (2–5 y old) and the dependence of that response on habitat type were analyzed. Using pitfall traps, beetles (Coleoptera) and ants (Formicidae) were sampled in replicated forest, scrub, and steppe areas including paired unburnt and burnt plots. A total of 176 species of beetles (8245 individuals) and 22 species of ants (115,056 individuals) were captured. Most beetle families (65%) were captured in the forest, while most ant species were most frequently captured in the steppe (45%). Beetle abundance was the same in unburnt and burnt plots in the three habitats, but ant abundance was higher in burnt than in unburnt plots. Fire usually decreased species richness of both taxa, but the strength of this effect depended on the habitat type. Coleoptera richness was lower in burnt than in unburnt plots in the forest and steppe but was the same in unburnt and burnt scrub plots. Ant richness was lower in burnt forest and scrub plots and was similar between ...

Asynchronous spermatogenesis and biennial female cycle of the viviparous lizard Phymaturus antofagastensis (Liolaemidae): reproductive responses to high altitudes and temperate climate of Catamarca, Argentina

Abstract: This paper studies minimum SVL at sexual maturity, sexual dimorphism, operational sex ratio, male and female reproductive cycles, and litter size of viviparous Phymaturus antofagastensis, a species living at high altitude in the temperate climate of Catamarca, Argentina. Males reached sexual maturity at 90 mm, and females at 79 mm. Adult males attained significantly larger body size and head width than adult females. Histological analysis showed asynchrony in spermatogenesis timing among males and spermatozoa storage in epididymis throughout the reproductive season (spring to early autumn). Females showed a biennial reproductive cycle taking at least one activity season to perform either vitellogenesis or pregnancy. Brood size resulted in two offspring, a condition similar to other species of the genus, with births occurring in late summer. The reproductive cycle of Phymaturus antofagastensis shows a new response in males and females to harsh environments characterized by short activity seasons, long hibernation periods and large daily and seasonal thermal fluctuations.

Current distribution and conservation of the huemul (Hippocamelus bisulcus) in Argentina and Chile

Abstract: ) is anendemic deer of the Andean-Patagonian for-ests of Argentina and Chile. Originally itsdistribution extended from 34 to 54o S in Chileand occupied areas of Andean forests andecotonal steppes of Argentina between 36 and52o S (Diaz, 2000). From the beginning of theEuropean colonization the distribution andabundance of this species began to declinedue to hunting pressure, destruction of habi-tat and predation by dogs, and probably alsodue to susceptibility to diseases of livestock,competition with domestic animals and intro-duced exotic species (Povilitis, 1998; Diaz andSmith-Flueck, 2000; Serret, 2001).The huemul has become extinct in the Chil-ean VI and VII administrative regions (34o-36oS). There are no current records of its pres-ence between 38 and 41o S in Chile or inMendoza and most of Neuquen provinces inArgentina (Lopez et al., 1998). At present, thespecies is classified as endangered (Glade,1988; Diaz and Ojeda, 2000; IUCN, 2000).The evaluation of thresholds of occurrenceand trends in distribution range is an impor-tant tool for the assessment of conservationstatus of species (IUCN, 2001). In spite of thefact that huemul are legally protected in bothcountries and that there have been efforts toconserve them since the 1930s, actions aimingat defining its distribution are recent (Serret,1992; Lopez et al., 1998; Diaz, 2000). We havestudied the current distribution of huemul andidentified the location of clusters of occur-rence in the context of existing protected ar-eas and administrative unit boundaries in bothChile and Argentina.The study area includes the coastal landsand the Andean foothills and highlands withinthe historical distribution of the species(Povilitis, 1998; Diaz, 2000). This area com-prises the provinces of Neuquen, Rio Negro,Chubut and Santa Cruz in Argentina and theVIII, IX, X, XI and XII regions in Chile.Records of current presence of huemul werebased on the data set of Lopez et al. (1998),the revision and analysis of “gray” literature,and interviews with park rangers, park war-dens and wildlife biologists fromAdministracion de Parques Nacionales ofArgentina (APN), Direcciones Provinciales deFauna in Argentina, Fundacion Vida SilvestreArgentina, Corporacion Nacional Forestal ofChile (CONAF), and Comite Nacional Pro

On period doubling bifurcations of cycles and the harmonic balance method

Abstract: This works attempts to give quasi-analytical expressions for subharmonic solutions appearing in the vicinity of a Hopf bifurcation. Starting with well-known tools as the graphical Hopf method for recovering the periodic branch emerging from classical Hopf bifurcation, precise frequency and amplitude estimations of the limit cycle can be obtained. These results allow to attain approximations for period doubling orbits by means of harmonic balance techniques, whose accuracy is established by comparison of Floquet multipliers with continuation software packages. Setting up a few coefficients, the proposed methodology yields to approximate solutions that result from a second period doubling bifurcation of cycles and to extend the validity limits of the graphical Hopf method.

Combined use of killer biotype and mtDNA-RFLP patterns in a Patagonian wine Saccharomyces cerevisiae diversity study.

Abstract: The aim of this work was to characterize the indigenous wine Saccharomyces cerevisiae diversity within the Argentinean Patagonia. Two cellars with particular enological practices located in different winegrowing areas were selected and 112 indigenous S. cerevisiae isolates were obtained from spontaneous red wine fermentations carried out in them. Thirty-five and 19 patterns were distinguished among the total indigenous isolates using mtDNA-RFLP and killer biotype analysis, respectively. The combination of both typing techniques rendered a higher variability with 42 different patterns, i.e. 42 strains, evidencing a great diversity in S. cerevisiae populations associated with spontaneous red wine fermentations in Northwestern Patagonia. The analysis of the relatedness among strains using Principal Coordinates Analysis from combined data allowed the clustering of the strains into two populations significantly related to their origin fermentations. The combined use of the mtDNA-RFLP analysis together with the killer biotype method proved to be a powerful tool in the fingerprinting of the enological S. cerevisiae strains.

Predation on snakes of Argentina: Effects of coloration and ring pattern on coral and false coral snakes

Abstract: The occurrence of coral snake coloration among unrelated venomous and non‐venomous snake species has often been explained in terms of warning coloration and mimicry. In Argentina, no field tests have been conducted to confirm this mimetic association between one venomous coral species (Micrurus phyrrocryptus, Elapidae) and two non‐venomous snake species with a similar color pattern (Lystrophis pulcher and Oxyrhopus rhombifer, Colubridae). The aims of this work were to test for the possible aposematic or cryptic function of the ring pattern and coloration of coral snakes and false coral snakes from central Argentina, and to analyse whether the pattern is effective throughout the year. Predation on snakes was estimated by using non‐toxic plasticine replicas of ringed venomous and non‐venomous snakes and unbanded green snakes placed along transects in their natural habitat during the dry and rainy season. Ringed color pattern was attacked by predators despite the background color. One of the replica types wa...

Trends on COTS component identification

Abstract: Identification of COTS candidates is a complex activity itself. It implies not only dealing with an impressive number of possible candidates but also with unstructured information that requires a careful analysis. In this context, some proposals currently use description logics to develop an ontology for matching requested and provided services, or propose taxonomies for classification; others suggest extending the identification stage with a learning phase, which provides support to the COTS component discovery process. In this paper, we present common features and differences among some of these proposals, identifying relevant issues for COTS component classification and identification in the near future.