Showing papers by "National University of Comahue published in 2010"

Erosion of lizard diversity by climate change and altered thermal niches.

Abstract: It is predicted that climate change will cause species extinctions and distributional shifts in coming decades, but data to validate these predictions are relatively scarce Here, we compare recent and historical surveys for 48 Mexican lizard species at 200 sites Since 1975, 12% of local populations have gone extinct We verified physiological models of extinction risk with observed local extinctions and extended projections worldwide Since 1975, we estimate that 4% of local populations have gone extinct worldwide, but by 2080 local extinctions are projected to reach 39% worldwide, and species extinctions may reach 20% Global extinction projections were validated with local extinctions observed from 1975 to 2009 for regional biotas on four other continents, suggesting that lizards have already crossed a threshold for extinctions caused by climate change

Building the bridge between animal movement and population dynamics

Abstract: While the mechanistic links between animal movement and population dynamics are ecologically obvious, it is much less clear when knowledge of animal movement is a prerequisite for understanding and predicting population dynamics. GPS and other technologies enable detailed tracking of animal location concurrently with acquisition of landscape data and information on individual physiology. These tools can be used to refine our understanding of the mechanistic links between behaviour and individual condition through ‘spatially informed’ movement models where time allocation to different behaviours affects individual survival and reproduction. For some species, socially informed models that address the movements and average fitness of differently sized groups and how they are affected by fission–fusion processes at relevant temporal scales are required. Furthermore, as most animals revisit some places and avoid others based on their previous experiences, we foresee the incorporation of long-term memory and intention in movement models. The way animals move has important consequences for the degree of mixing that we expect to find both within a population and between individuals of different species. The mixing rate dictates the level of detail required by models to capture the influence of heterogeneity and the dynamics of intra- and interspecific interaction.

The interpretation of habitat preference metrics under use–availability designs

Abstract: Models of habitat preference are widely used to quantify animal–habitat relationships, to describe and predict differential space use by animals, and to identify habitat that is important to an animal (i.e. that is assumed to influence fitness). Quantifying habitat preference involves the statistical comparison of samples of habitat use and availability. Preference is therefore contingent upon both of these samples. The inferences that can be made from use versus availability designs are influenced by subjectivity in defining what is available to the animal, the problem of quantifying the accessibility of available resources and the framework in which preference is modelled. Here, we describe these issues, document the conditional nature of preference and establish the limits of inferences that can be drawn from these analyses. We argue that preference is not interpretable as reflecting the intrinsic behavioural motivations of the animal, that estimates of preference are not directly comparable among different samples of availability and that preference is not necessarily correlated with the value of habitat to the animal. We also suggest that preference is context-dependent and that functional responses in preference resulting from changing availability are expected. We conclude by describing advances in analytical methods that begin to resolve these issues.

Stochastic modelling of animal movement

Abstract: Modern animal movement modelling derives from two traditions. Lagrangian models, based on random walk behaviour, are useful for multi-step trajectories of single animals. Continuous Eulerian models describe expected behaviour, averaged over stochastic realizations, and are usefully applied to ensembles of individuals. We illustrate three modern research arenas. (i) Models of home-range formation describe the process of an animal ‘settling down’, accomplished by including one or more focal points that attract the animal's movements. (ii) Memory-based models are used to predict how accumulated experience translates into biased movement choices, employing reinforced random walk behaviour, with previous visitation increasing or decreasing the probability of repetition. (iii) Levy movement involves a step-length distribution that is over-dispersed, relative to standard probability distributions, and adaptive in exploring new environments or searching for rare targets. Each of these modelling arenas implies more detail in the movement pattern than general models of movement can accommodate, but realistic empiric evaluation of their predictions requires dense locational data, both in time and space, only available with modern GPS telemetry.

A revised classification of Santalales

Abstract: We present here a revised classification of Santalales, an angiosperm order that contains 18 families, 160 genera, and over 2200 species. Both nonparasitic and parasitic flowering plants occur in the traditionally circumscribed family Olacaceae whereas all other families are composed entirely of parasites. The five evolutionary radiations of aerial parasitism produced mistletoes that constitute most of the generic and specific diversity seen in the order. This classification, although based primarily upon results from molecular phylogenetic investigations, brings together all currently available information that contributes to our understanding of relationships among these plants. Monophyletic groups (clades) obtained from molecular analyses were named using a Linnaean ranked system. Four new families are named that formerly resided in Santalaceae s.l.: Amphorogynaceae, Cervantesiaceae, Comandraceae, and Nanodeaceae. A new tribal and subtribal classification for Loran- thaceae is presented where nine new subtribe names are proposed.

Floral adaptation and diversification under pollen limitation

Abstract: Pollen limitation (PL) of seed production creates unique conditions for reproductive adaptation by angiosperms, in part because, unlike under ovule or resource limitation, floral interactions with pollen vectors can contribute to variation in female success. Although the ecological and conservation consequences of PL have received considerable attention in recent times, its evolutionary implications are poorly appreciated. To identify general influences of PL on reproductive adaptation compared with those under other seed-production limits and their implications for evolution in altered environments, we derive a model that incorporates pollination and post-pollination aspects of PL. Because PL always favours increased ovule fertilization, even when population dynamics are not seed limited, it should pervasively influence selection on reproductive traits. Significantly, under PL the intensity of inbreeding does not determine whether outcrossing or autonomous selfing can evolve, although it can affect which response is most likely. Because the causes of PL are multifaceted in both natural and anthropogenically altered environments, the possible outcrossing solutions are diverse and context dependent, which may contribute to the extensive variety of angiosperm reproductive characteristics. Finally, the increased adaptive options available under PL may be responsible for positive global associations between it and angiosperm diversity.

Birds as suppliers of seed dispersal in temperate ecosystems: conservation guidelines from real-world landscapes.

Abstract: Seed dispersal by animals is considered a pivotal ecosystem function that drives plant-community dynamics in natural habitats and vegetation recovery in human-altered landscapes. Nevertheless, there is a lack of suitable ecological knowledge to develop basic conservation and management guidelines for this ecosystem service. Essential questions, such as how well the abundance of frugivorous animals predicts seeding function in different ecosystems and how anthropogenic landscape heterogeneity conditions the role of dispersers, remain poorly answered. In three temperate ecosystems, we studied seed dispersal by frugivorous birds in landscape mosaics shaped by human disturbance. By applying a standardized design across systems, we related the frequency of occurrence of bird-dispersed seeds throughout the landscape to the abundance of birds, the habitat features, and the abundance of fleshy fruits. Abundance of frugivorous birds in itself predicted the occurrence of dispersed seeds throughout the landscape in all ecosystems studied. Even those landscape patches impoverished due to anthropogenic disturbance received some dispersed seeds when visited intensively by birds. Nonetheless, human-caused landscape degradation largely affected seed-deposition patterns by decreasing cover of woody vegetation or availability of fruit resources that attracted birds and promoted seed dispersal. The relative role of woody cover and fruit availability in seed dispersal by birds differed among ecosystems. Our results suggest that to manage seed dispersal for temperate ecosystem preservation or restoration one should consider abundance of frugivorous birds as a surrogate of landscape-scale seed dispersal and an indicator of patch quality for the dispersal function; woody cover and fruit resource availability as key landscape features that drive seedfall patterns; and birds as mobile links that connect landscape patches of different degrees of degradation and habitat quality via seed deposition.

Factors influencing zooplankton size structure at contrasting temperatures in coastal shallow lakes: Implications for effects of climate change

Abstract: We assessed the importance of temperature, salinity, and predation for the size structure of zooplankton and provided insight into the future ecological structure and function of shallow lakes in a warmer climate. Artificial plants were introduced in eight comparable coastal shallow brackish lakes located at two contrasting temperatures: cold-temperate and Mediterranean climate region. Zooplankton, fish, and macroinvertebrates were sampled within the plants and at open-water habitats. The fish communities of these brackish lakes were characterized by small-sized individuals, highly associated with submerged plants. Overall, higher densities of small planktivorous fish were recorded in the Mediterranean compared to the cold-temperate region, likely reflecting temperature-related differences as have been observed in freshwater lakes. Our results suggest that fish predation is the major control of zooplankton size structure in brackish lakes, since fish density was related to a decrease in mean body size and density of zooplankton and this was reflected in a unimodal shaped biomass-size spectrum with dominance of small sizes and low size diversity. Salinity might play a more indirect role by shaping zooplankton communities toward more salt-tolerant species. In a global-warming perspective, these results suggest that changes in the trophic structure of shallow lakes in temperate regions might be expected as a result of the warmer temperatures and the potentially associated increases in salinity. The decrease in the density of largebodied zooplankton might reduce the grazing on phytoplankton and thus the chances of maintaining the clear water state in these ecosystems.

Introduced deer reduce native plant cover and facilitate invasion of non-native tree species: evidence for invasional meltdown

Abstract: Invasive species are a major threat to native communities and ecosystems worldwide. One factor frequently invoked to explain the invasiveness of exotic species is their release in the new habitat from control by natural enemies (enemy-release hypothesis). More recently, interactions between exotic species have been proposed as a potential mechanism to facilitate invasions (invasional melt- down hypothesis). We studied the effects of intro- duced deer on native plant communities and exotic plant species on an island in Patagonia, Argentina using five 400 m 2 exclosures paired with control areas in an Austrocedrus chilensis native forest stand. We hypothesized that introduced deer modify native understory composition and abundance and facilitate invasion of introduced tree species that have been widely planted in the region. After 4 years of deer exclusion, native Austrocedrus and exotic Pseudots- uga menziesii tree sapling abundances are not differ- ent inside and outside exclosures. However, deer browsing has strongly inhibited growth of native tree saplings (relative height growth is 77% lower with deer present), while exotic tree sapling growth is less affected (relative height growth is 3.3% lower). Deer significantly change abundance and composition of native understory plants. Cover of native plants in exclosures increased while cover in controls remained constant. Understory composition in exclosures after only 4 years differs greatly from that in controls, mainly owing to the abundance of highly-browsed native species. This study shows that introduced deer can aid the invasion of non-native tree species through negatively affecting native plant species.

Changes in the distribution of native fishes in response to introduced species and other anthropogenic effects

Abstract: Aim Globally, one of the major threats to the integrity of native faunas is the loss of biodiversity that can result from the introduction of exotics. Here we document recent changes in the distribution of five common fish species that are linked to introductions in Chile. Location Chile from 28° S to 54° S. Methods We assess the extent of changes in distribution of galaxiid species by comparing their historical and current distributions based on the results of the most extensive survey of freshwater fishes in Chile to date, a range that encompasses the full latitudinal and elevational range of the Galaxiidae in Chile. We test for relationships of the distributions and abundances of native fishes with the incidence of introduced species. Results The latitudinal range of Galaxias maculatus has declined by 26%, and most of this reduction has occurred in the northern part of its range. Aplochiton taeniatus and Brachygalaxias bullocki have experienced reductions (8–17% loss) in total drainage area occupied, and they have disappeared from, or are now extremely difficult to find, in latitudes 36° to 41° S, coincidently with areas of urban growth and intense economic activities. The distribution of Galaxias platei has, instead, increased considerably. In northern basins, G. maculatus has apparently been replaced by an introduced poeciliid Gambusia sp. High-elevation systems remain dominated by native Galaxias platei, whereas systems at intermediate elevations, especially rivers, are now dominated by introduced salmonids. Within drainages, native galaxiids remain abundant where exotic salmonid abundance is low. Main conclusions We suggest that negative interactions between introduced and native fish are responsible for some of the range reductions among Galaxiidae in Chile. The severity of the impacts varies with latitude and altitude and is probably related to temperature. The effects of Gambusia are restricted to warmer systems. Native fish also appear to have found temperature refugia from salmonids; impacts are low in the warmer northern and coastal systems, as well as in high-altitude relatively cold systems. Native fish also appear less vulnerable to salmonids in lakes than in rivers. This study identifies watersheds critical for the conservation of biodiversity within the Galaxiidae.

Out in the cold: genetic variation of Nothofagus pumilio (Nothofagaceae) provides evidence for latitudinally distinct evolutionary histories in austral South America

Abstract: Nothofagus pumilio is the dominant and almost ubiquitous tree species in mountainous environments of temperate South America. We used two types of molecular markers (cpDNA and isozymes) to evaluate the effects of the Paleogene paleogeography of Patagonia and more recent climatic oscillations of the Neogene on such cold-tolerant species’ genetic makeup. Phylogeographic analysis on sequences of three cpDNA non-coding regions at 85 populations yielded two latitudinally disjunct monophyletic clades north and south of c. 42°S containing 11 and three haplotypes, respectively. This indicates a long-lasting vicariant event due to the presence of an extended open paleobasin at mid latitudes of Patagonia. Also distribution patterns of cpDNA haplotypes suggest regional spread following stepping-stone models using pre-Cenozoic mountains as corridors. Comparable genetic diversity measured along 41 sampled populations using seven polymorphic isozyme loci provides evidence of local persistence and spread from multiple ice-free locations. In addition, significantly higher heterozygosity and allelic richness at high latitudes, i.e. in areas of larger glacial extent, suggest survival in large and isolated refugia. While, higher cpDNA diversity in lower latitudes reflects the complex orogeny that historically isolated northern populations, lower isozyme diversity and reduced FST values provide evidence of local glacial survival in numerous small locales. Therefore, current genetic structure of N. pumilio is the result of regional processes which took place during the Tertiary that were enhanced by contemporary local effects of drift and isolation in response to Quaternary climatic cycles.

Direct effects of habitat area on interaction diversity in pollination webs.

Abstract: Island biogeography theory predicts that species richness increases with habitat area and declines with isolation. We expand this framework to address changes in the number of links and species in pollination webs from 12 isolated hills, ranging in area from tens to thousands of hectares, immersed in the agriculture matrix of the Argentine Pampas. We also studied whether total interaction frequency is partitioned more evenly among individual links in richer webs. Our results reveal a direct effect of area on the number of links and species present in each pollination web. However, link richness increased twofold faster than species richness with area. These area effects were not confounded by sampling effort or correlated incidence of exotic species, despite widespread habitat disturbance. Habitat proximity, an inverse measure of isolation, had a marginally significant influence on link but not on species richness. Increased link number was associated with decreasing dominance by any particular interaction and increasing interaction evenness. Despite the strong area effect, a rich pollination web sampled from a small, protected sierra suggests that simple conservation measures, such as reduced grazing and fire suppression, may effectively preserve much local interaction diversity.

Life in soil by the actinorhizal root nodule endophyte Frankia. A review

Abstract: Frankia is a genus of soil actinomycetes famous for its ability to form N2-fixing root nodule symbioses with actinorhizal plants. Although Frankia strains display a high diversity in terms of ecological niches in soil, current knowledge about Frankia is dominated by its life as an endophyte in root nodules. Increased use of molecular methods has refined and expanded insights into endophyte-host specificities and Frankia phylogeny. This review has focus on Frankia as a soil organism, including its part of microbial consortia, and how to study Frankia in soil. We highlight the use of nodulation tests and molecular methods to reveal population size and genetic diversity of Frankia in soil and discuss how autoregulation of nodulation and interactions with other soil microorganisms may influence the results. A comprehensive record of published interactions between Frankia and other soil microbes is summarized.

Winners and losers in human-made habitats: interspecific competition outcomes in two Neotropical vultures

Abstract: Understanding the factors underlying species coexistence is a major focus in community ecology. When dealing with competition between native and exotic species, the competitive exclusion of the ‘weaker’ species can have consequences for biodiversity conservation. We examined interspecific interactions during foraging between black vultures Coragyps atratus and Andean condors Vultur gryphus in Southern Argentina. Previous studies suggest facilitatory interactions between them. However, in most parts of their distribution ranges, these species did not coexist until recently, when black vultures expanded their geographic range following human development. Thus, facilitatory processes or segregation patterns could not be fine-tuned enough to allow their coexistence. Our hypothesis is that black vultures and Andean condors compete for food resources, and that this competitive scenario can change depending on local species abundances and habitat humanization. We experimentally placed sheep carcasses in two habitats differing in degrees of humanization to study the foraging patterns in these species. Both species exploited carcasses with similar temporal patterns. However, the first to arrive and the dominant species were different in both habitats, according to their abundances. Although black vultures do not completely prevent the arrival of Andean condors to carcasses, they represent serious obstacles for feeding. Thus, while dominance hierarchy at carcasses could be related to body size, carcass consumption was determined by species abundance. Our results support the hypothesis that the expansion of a ‘winning’ species may trigger interspecific competition with other ‘loser’ species, with negative responses towards human activities when they became abundant. Although the results are not conclusive, invasion and extinction processes could be occurring and they can have serious consequences for the diversity (i.e. richness and evenness) of the New World scavenger guilds.

Differential effects of climate variability on forest dynamics along a precipitation gradient in northern Patagonia

Abstract: Summary1. The understanding of the impacts of climate anomalies on demographic processes involvedin forest dynamics is becoming a major global change research objective, as climate-drivendemographic changes have the potential to alter ecological processes and change the compositionofexistingcommunities.2. Here, we test whether the effects of climatic variability on Nothofagus dombeyi forest dynamicsdiffer along the W–E precipitation gradient of northern Patagonia, Argentina, due to differentcontrollingfactorsalongthegradient.3. Using a dendroecological approach, we sampled six N. dombeyi stands along the gradient. Treedeath,growthreleaseandsaplingbirthdateswereobtainedandusedtoreconstructstandmortality,canopydisturbanceandestablishmentpatternsineachstand.Discreteextremeclimaticeventswereobtained by applying thresholds to meteorological time series. Bivariate event analysis wasperformed to examine the temporal relationships between climate events and forest demographicandcanopydisturbancepatterns.4. In the xeric region, forest dynamics is driven by drought/heat and humid events. Followingdrought/heat events we observed standing-dead tree mortality, releases in growth, and tree estab-lishment episodes. Regional synchrony of these events was coincident with droughts registered fornorthern Patagonia. However, successful establishment was related to wet periods that occurredafter drought events, showing the dependence on favourable periods for growth. For wet regions,demographic patterns showed a temporally uniform pattern but with synchronies at the regionaland local scales. Canopy openings produced by fallen trees, and consequent release in growth andestablishment, were related to both drought and snowy/windy years. The effect of drought in wetregionforestswasrelatedmainlytotheextreme1998–99droughtinnorthernPatagonia.5. Synthesis. Climate in northern Patagonia influences N. dombeyi forest dynamics differentiallyalong a precipitation gradient. In xeric forests, strong but relatively short climatic fluctuationsimpact forest structure through direct effects on tree demography. In wet forests, climatic-inducedmechanical disturbance prevails, driving mortality and subsequent growth and establishment.Considering that recent extreme droughts have the strongest negative impact on N. dombeyipopulations at the eastern distributional limits, a change in distribution of this species as aconsequenceofprojectedclimatechangeisexpected.Key-words: drought, establishment rates, extreme climatic events, forest dynamics, Nothofagusdombeyi, plant–climate interactions, release events, tree mortalityIntroduction

Effects of anthropogenic habitat disturbance on local pollinator diversity and species turnover across a precipitation gradient

Abstract: Anthropogenic habitat disturbance can have profound effects on multiple components of forest biotas including pollinator assemblages. We assessed the effect of small-scale disturbance on local richness, abundance, diversity and evenness of insect pollinator fauna; and how habitat disturbance affected species turnover across the landscape and overall diversity along a precipitation gradient in NW Patagonia (Argentina). We evaluated the effect of disturbance on overall pollinator fauna and then separately for bees (i.e. Apoidea) and non-bee pollinators. Locally, disturbed habitats had significantly higher pollinator species richness and abundances than undisturbed habitats for the whole pollinator assemblage, but not for bees or non-bees separately. However, significant differences in species richness between habitats vanished after accounting for differences in abundance between habitat types. At a local scale Shannon–Weaver diversity and evenness did not vary with disturbance. A β diversity index indicated that, across forest types, species turnover was lower between disturbed habitats than between undisturbed habitats. In addition, rarefaction curves showed that disturbed habitats as a whole accumulated fewer species than undisturbed habitats at equivalent sample sizes. We concluded that small patches of disturbed habitat have a negligible effect on local pollinator diversity; however, habitat disturbance reduced β diversity through a homogenization of the pollinator fauna (in particular of bees) across the landscape.

Factors controlling seed predation by rodents and non-native Sus scrofa in Araucaria araucana forests: potential effects on seedling establishment

Abstract: Post-dispersal seed predation can severely limit plant recruitment, but its ultimate impact could be modulated by environmental factors and by the composition of the granivore guild. Here, we analyze the relative impact of the non-native wild boar and native rodents on seed survival and seedling establishment of the mast conifer Araucaria araucana. Predation, seed survival and seedling establishment were measured at different microsites and distances from 11 isolated trees in Lanin National Park (Argentina) over a period of marked fluctuation in seed production. Wild boar consumed between 10 and 30% of available seeds on a 13-day period, threefold less than rodents. Wild boar predation was mainly affected by forest canopy composition, while microsite conditions influenced both kind of predators, with high chronic rodent predation underneath dense vegetation and moderate (but interannually variable) wild boar predation at poorly vegetated microsites. Predation by rodents was spatially clustered at the microsite scale, particularly during non-mast years; while predation by wild boar was spatially structured at a coarser scale and less modified by masting. The exclusion of wild boar increased significantly the amount of surviving seeds, resulting in higher seedling establishment in intermediate production years, but not affecting it during the mast year. At tree level, seedling establishment was negatively correlated with predation; while at stand level, cone production accounted for most of the seedling establishment variability. The current wild boar population may not be affecting the seedling establishment at population scale, probably due to minimization of its impact by the Araucaria masting strategy. However, if wild boar population numbers continue to increase, their impact may shift from individual tree scale to stand scale, threatening Araucaria forest regeneration.

A framework to improve communication during the requirements elicitation process in GSD projects

Abstract: Achieving a shared understanding of requirements is difficult in any situation, even more so in global software development projects. In such environments, people must deal not only with the lack of face to face communication, but also with other issues such as time difference, cultural diversity and a large amount of information originating from different sources throughout the world. Obtaining the right requirements therefore implies extra effort. In order to minimize such problems, we propose a framework that focuses on analyzing the factors that may be problematic in global software development and which suggests a set of strategies to improve the requirements elicitation process in such environments. In this paper, we describe the different phases of our framework and present the results of an experiment that test part of this framework. The results indicate that applying some of the strategies proposed in the framework seems to positively affect the stakeholders’ satisfaction with regard to communication. Moreover, the quality of the written software requirements specifications seems to be better as well when using those strategies.

Risk of predation and behavioural response in three anuran species: influence of tadpole size and predator type.

Abstract: Many species alter their activity, microhabitat use, morphology and life history in response to predators. Predation risk is related to predator size and palatability of prey among others factors. We analyzed the predation risk of three species of tadpoles that occur in norwestern Patagonia, Argentina: Pleurodema thaul, Pleurodema bufoninum and Rhinella spinulosa. We sampled aquatic insect predators in 18 ponds to determine predator-tadpole assemblage in the study area. In laboratory conditions, we analysed the predation rate imposed by each predator on each tadpole species at different tadpole sizes. Finally, we tested whether tadpoles alter their activity in the presence of chemical and visual cues from predators. Small P. thaul and P. bufoninum tadpoles were the most vulnerable prey species, while small R. spinulosa tadpoles were only consumed by water bugs. Dragonflies and water bugs were the most dangerous tadpole predators. Small P. thaul tadpoles reduced their activity when they were exposed to all predators, while large tadpoles only reduced the activity in the presence of large predators (dragonfly larvae and water bugs). Small P. bufoninum tadpoles reduced the activity when they were exposed to beetle larvae and dragonfly larvae, while large tadpoles only reduced activity when they were exposed to larger predators (water bugs and dragonfly larvae). R. spinulosa tadpoles were the less sensitive to presence of predators, only larger tadpoles responded significantly to dragonfly larvae by reducing their activity. We conclude that behavioural responses of these anuran species were predator-specific and related to the risk imposed by each predator.