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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 04 March 2014, Vol.111(9), pp.3484-9
    Description: Determining how widespread human-induced changes such as habitat loss, landscape fragmentation, and climate instability affect populations, communities, and ecosystems is one of the most pressing environmental challenges. Critical to this challenge is understanding how these changes are affecting the movement abilities and dispersal trajectories of organisms and what role conservation planning can play in promoting movement among remaining fragments of suitable habitat. Whereas evidence is mounting for how conservation strategies such as corridors impact animal movement, virtually nothing is known for species dispersed by wind, which are often mistakenly assumed to not be limited by dispersal. Here, we combine mechanistic dispersal models, wind measurements, and seed releases in a large-scale experimental landscape to show that habitat corridors affect wind dynamics and seed dispersal by redirecting and bellowing airflow and by increasing the likelihood of seed uplift. Wind direction interacts with landscape orientation to determine when corridors provide connectivity. Our results predict positive impacts of connectivity and patch shape on species richness of wind-dispersed plants, which we empirically illustrate using 12 y of data from our experimental landscapes. We conclude that habitat fragmentation and corridors strongly impact the movement of wind-dispersed species, which has community-level consequences.
    Keywords: Diversity ; Habitat Structure ; Long-Distance Dispersal ; Plant Community ; Reserve Design ; Biodiversity ; Ecosystem ; Models, Biological ; Wind ; Plant Physiological Phenomena -- Physiology ; Seed Dispersal -- Physiology
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    In: New Phytologist, January 2013, Vol.197(2), pp.655-667
    Description: Seed size and dormancy are reproductive traits that interact as adaptations to environmental conditions. Here, we explore the evolution of these traits in environments that differ in overall mean favorability and in the extent of temporal predictability. Our model simulates a population of annual plants living in a range of environments that differ in aridity, namely mean annual precipitation and inter‐annual variation of this mean precipitation. The optimal fitness curve is investigated assuming density dependence, three alternative hypothetical relationships between seed mass and seed survival in the soil (negative, positive, and independent of mass), and three alternative relationships between survival in soil and precipitation (strong and intermediate negative relationships, and no relationship). Our results show that seed size and dormancy are not two substitutable evolutionary traits; that specific combinations of these two traits are selected in environments that differ in favorability and temporal predictability; that a certain degree of seed dormancy is advantageous not only in temporally unpredictable environments but also in temporally predictable environments with high competition; and that more than one combination of seed size and dormancy (defined in terms of germination fraction) can be optimal, even in spatially homogeneous environments, potentially allowing selection for more variation in these traits within and among species.
    Keywords: Bet Hedging ; Dormancy ; Precipitation ; Seed Mass ; Seed Traits ; Temporal Heterogeneity
    ISSN: 0028-646X
    E-ISSN: 1469-8137
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  • 3
    Language: English
    In: 2012, Vol.7(11), p.e48766
    Description: Independence between observations is a standard prerequisite of traditional statistical tests of association. This condition is, however, violated when autocorrelation is present within the data. In the case of variables that are regularly sampled in space (i.e. lattice data or images), such as those provided by remote-sensing or geographical databases, this problem is particularly acute. Because analytic derivation of the null probability distribution of the test statistic (e.g. Pearson's r) is not always possible when autocorrelation is present, we propose instead the use of a Monte Carlo simulation with surrogate data. ; The null hypothesis that two observed mapped variables are the result of independent pattern generating processes is tested here by generating sets of random image data while preserving the autocorrelation function of the original images. Surrogates are generated by matching the dual-tree complex wavelet spectra (and hence the autocorrelation functions) of white noise images with the spectra of the original images. The generated images can then be used to build the probability distribution function of any statistic of association under the null hypothesis. We demonstrate the validity of a statistical test of association based on these surrogates with both actual and synthetic data and compare it with a corrected parametric test and three existing methods that generate surrogates (randomization, random rotations and shifts, and iterative amplitude adjusted Fourier transform). Type I error control was excellent, even with strong and long-range autocorrelation, which is not the case for alternative methods. ; The wavelet-based surrogates are particularly appropriate in cases where autocorrelation appears at all scales or is direction-dependent (anisotropy). We explore the potential of the method for association tests involving a lattice of binary data and discuss its potential for validation of species distribution models. An implementation of the method in Java for the generation of wavelet-based surrogates is available online as supporting material.
    Keywords: Research Article ; Biology ; Computer Science ; Earth Sciences ; Social And Behavioral Sciences ; Computer Science
    E-ISSN: 1932-6203
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  • 4
    In: Nature, 2013, Vol.499(7458), p.324
    Description: Terrestrial plants remove C[O.sub.2] from the atmosphere through photosynthesis, a process that is accompanied Sy the loss of water vapour from leaves (1). The ratio of water loss to carbon gain, or water-use efficiency, is a key characteristic of ecosystem function that is central to the global cycles of water, energy and carbon (2). Here we analyse direct, long-term measurements of whole-ecosystem carbon and water exchange (3). We find a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades. We systematically assess various competing hypotheses to explain this trend, and find that the observed increase is most consistent with a strong C[O.sub.2] fertilization effect. The results suggest a partial closure of stomata (1)--small pores on the leaf surface that regulate gas exchange--to maintain a nearconstant concentration of C[O.sub.2] inside the leaf even under continually increasing atmospheric C[O.sub.2] levels. The observed increase in forest water-use efficiency is larger than that predicted by existing theory and 13 terrestrial biosphere models. The increase is associated with trends of increasing ecosystem-level photosynthesis and net carbon uptake, and decreasing evapotranspiration. Our findings suggest a shift in the carbon- and water-based economics of terrestrial vegetation, which may require a reassessment of the role of stomatal control in regulating interactions between forests and climate change, and a re-evaluation of coupled vegetation-climate models.
    Keywords: Water -- Research ; Water -- Measurement ; Atmospheric Carbon Dioxide -- Research ; Atmospheric Carbon Dioxide -- Measurement;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 5
    In: Ecology, September 2011, Vol.92(9), pp.1818-1827
    Description: The even‐aged northern hardwood forests of the Upper Great Lakes Region are undergoing an ecological transition during which structural and biotic complexity is increasing. Early‐successional aspen ( spp.) and birch () are senescing at an accelerating rate and are being replaced by middle‐successional species including northern red oak (), red maple (), and white pine (). Canopy structural complexity may increase due to forest age, canopy disturbances, and changing species diversity. More structurally complex canopies may enhance carbon (C) sequestration in old forests. We hypothesize that these biotic and structural alterations will result in increased structural complexity of the maturing canopy with implications for forest C uptake. At the University of Michigan Biological Station (UMBS), we combined a decade of observations of net primary productivity (NPP), leaf area index (LAI), site index, canopy tree‐species diversity, and stand age with canopy structure measurements made with portable canopy lidar (PCL) in 30 forested plots. We then evaluated the relative impact of stand characteristics on productivity through succession using data collected over a nine‐year period. We found that effects of canopy structural complexity on wood NPP (NPP) were similar in magnitude to the effects of total leaf area and site quality. Furthermore, our results suggest that the effect of stand age on NPP is mediated primarily through its effect on canopy structural complexity. Stand‐level diversity of canopy‐tree species was not significantly related to either canopy structure or NPP. We conclude that increasing canopy structural complexity provides a mechanism for the potential maintenance of productivity in aging forests.
    Keywords: Canopy Structure ; Carbon Sequestration ; Diversity ; Forest ; Lidar ; Net Primary Production ; Rugosity
    ISSN: 0012-9658
    E-ISSN: 1939-9170
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  • 6
    In: Nature, 2014, Vol.507(7491), p.E2
    Keywords: Ecosystem ; Carbon Dioxide -- Analysis ; Trees -- Chemistry ; Water -- Analysis;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 7
    Language: English
    In: PLoS ONE, 2012, Vol.7(1), p.e30569
    Description: Pest control is one of the areas in which population dynamic theory has been successfully applied to solve practical problems. However, the links between population dynamic theory and model construction have been less emphasized in the management and control of weed populations. Most management models of weed population dynamics have emphasized the role of the endogenous process, but the role of exogenous variables such as climate have been ignored in the study of weed populations and their management. Here, we use long-term data (22 years) on two annual weed species from a locality in Central Spain to determine the importance of endogenous and exogenous processes (local and large-scale climate factors). Our modeling study determined two different feedback structures and climate effects in the two weed species analyzed. While Descurainia s ophia exhibited a second-order feedback and low climate influence, Veronica hederifolia was characterized by a first-order feedback structure and important effects from temperature and rainfall. Our results strongly suggest the importance of theoretical population dynamics in understanding plant population systems. Moreover, the use of this approach, discerning between the effect of exogenous and endogenous factors, can be fundamental to applying weed management practices in agricultural systems and to controlling invasive weedy species. This is a radical change from most approaches currently used to guide weed and invasive weedy species managements.
    Keywords: Research Article ; Agriculture ; Biology ; Earth Sciences ; Plant Biology ; Ecology
    E-ISSN: 1932-6203
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  • 8
    Language: English
    In: PLoS ONE, 2012, Vol.7(1), p.e31170
    Description: Climate warming may drive invasions by exotic plants, thereby raising concerns over the risks of invasive plants. However, little is known about how climate warming influences the growth and competitive ability of exotic plants from their home and introduced ranges. We conducted a common garden experiment with an invasive plant Centaurea maculosa and a native plant Poa pratensis , in which a mixture of sand and vermiculite was used as a neutral medium, and contrasted the total biomass, competitive effects, and competitive responses of C. maculosa populations from Europe (home range) and North America (introduced range) under two different temperatures. The warming-induced inhibitory effects on the growth of C. maculosa alone were stronger in Europe than in North America. The competitive ability of C. maculosa plants from North America was greater than that of plants from Europe under the ambient condition whereas this competitive ability followed the opposite direction under the warming condition, suggesting that warming may enable European C. maculosa to be more invasive. Across two continents, warming treatment increased the competitive advantage instead of the growth advantage of C. maculosa , suggesting that climate warming may facilitate C. maculosa invasions through altering competitive outcomes between C. maculosa and its neighbors. Additionally, the growth response of C. maculosa to warming could predict its ability to avoid being suppressed by its neighbors.
    Keywords: Research Article ; Biology ; Earth Sciences ; Plant Biology ; Ecology
    E-ISSN: 1932-6203
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  • 9
    Language: English
    In: 2012, Vol.7(11), p.e50441
    Description: High-latitude northern ecosystems are experiencing rapid climate changes, and represent a large potential climate feedback because of their high soil carbon densities and shifting disturbance regimes. A significant carbon flow from these ecosystems is soil respiration ( R S , the flow of carbon dioxide, generated by plant roots and soil fauna, from the soil surface to atmosphere), and any change in the high-latitude carbon cycle might thus be reflected in R S observed in the field. This study used two variants of a machine-learning algorithm and least squares regression to examine how remotely-sensed canopy greenness (NDVI), climate, and other variables are coupled to annual R S based on 105 observations from 64 circumpolar sites in a global database. The addition of NDVI roughly doubled model performance, with the best-performing models explaining ∼62% of observed R S variability. We show that early-summer NDVI from previous years is generally the best single predictor of R S , and is better than current-year temperature or moisture. This implies significant temporal lags between these variables, with multi-year carbon pools exerting large-scale effects. Areas of decreasing R S are spatially correlated with browning boreal forests and warmer temperatures, particularly in western North America. We suggest that total circumpolar R S may have slowed by ∼5% over the last decade, depressed by forest stress and mortality, which in turn decrease R S . Arctic tundra may exhibit a significantly different response, but few data are available with which to test this. Combining large-scale remote observations and small-scale field measurements, as done here, has the potential to allow inferences about the temporal and spatial complexity of the large-scale response of northern ecosystems to changing climate.
    Keywords: Research Article ; Agriculture ; Biology ; Earth Sciences ; Chemistry ; Computer Science
    E-ISSN: 1932-6203
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  • 10
    Language: English
    In: 2012, Vol.7(10), p.e44727
    Description: The Mediterranean region is one of the hot spots of climate change. This study aims at understanding what are the conditions sustaining tree diversity in Mediterranean wet forests under future scenarios of altered hydrological regimes. The core of the work is a quantitative, dynamic model describing the coexistence of different Mediterranean tree species, typical of arid or semi-arid wetlands. Two kind of species, i.e. Hygrophilous (drought sensitive, flood resistant) and Non-hygrophilous (drought resistant, flood sensitive), are broadly defined according to the distinct adaptive strategies of trees against water stress of summer drought and winter flooding. We argue that at intermediate levels of water supply the dual role of water (resource and stress) results in the coexistence of the two kind of species. A bifurcation analysis allows us to assess the effects of climate change on the coexistence of the two species in order to highlight the impacts of predicted climate scenarios on tree diversity. Specifically, the model has been applied to Mediterranean coastal swamp forests of Central Italy located at Castelporziano Estate and Circeo National Park. Our results show that there are distinct rainfall thresholds beyond which stable coexistence becomes impossible. Regional climatic projections show that the lower rainfall threshold may be approached or crossed during the XXI century, calling for an urgent adaptation and mitigation response to prevent biodiversity losses.
    Keywords: Research Article ; Biology ; Mathematics ; Plant Biology ; Ecology ; Mathematics
    E-ISSN: 1932-6203
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