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36 results for “Aridity gradient”
Evenness response to aridity gradients: Data required for Smith et al. 2022 Oecologia
These are the required data to do all analyses in Smith et al. 2022 in Oecologia using the assembled database across gradients. Included are the richness, evenness, and site level abiotic data. Paper abstract: We sought to understand the role that water availability (expressed as an aridity index) plays in determining regional and global patterns of richness and evenness, and in turn how these water availability-diversity relationships may result in different richness-evenness relationships at regional and global scales. We examined relationships between water availability, richness and evenness for eight grassy biomes spanning broad water availability gradients on five continents. Our study found that relationships between richness and water availability switched from positive for drier (South Africa, Tibet and USA) vs. negative for wetter (India) biomes, though were not significant for the remaining biomes. In contrast, only the India biome showed a significant relationship between water availability and evenness, which was negative. Globally, the richness-water availability relationship was hump-shaped, however, not significant for evenness. At the regional scale, a positive richness-evenness relationship was found for grassy biomes in India and Inner Mongolia, China. In contrast, this relationship was weakly concave-up globally. These results suggest that different, independent factors are determining patterns of species richness and evenness in grassy biomes, resulting in differing richness-evenness relationships at regional and global scales. As a consequence, richness and evenness may respond very differently across spatial gradients to anthropogenic changes, such as climate change.
SNE01 Species richness, community evenness (Evar) and ANPP effects of nitrogen addition across a gradient of 8 levels in a semi-arid shortgrass steppe and a mesic tallgrass prairie, 2014-2018
This dataset contains the first five years (2014-2018) of the effect of nitrogen addition on species richness, species evenness (Evar) and productivity for a long-term nitrogen addition gradient experiment in two North American grasslands: a semi-arid shortgrass steppe and a mesic tallgrass prairie. Fertilization with time-release urea has been on-going since 2014 in a gradient of eight levels: 0, 2.5, 5, 10, 15, 20, 30 g/m-2. The effect of nitrogen on richness, evenness and Aboveground Net Primary Productivity (ANPP g/m-2 yr) is calculated as the absolute change in value from control plots to treatment plots within each block.
Trait functional diversity explains mixture effects on litter decomposition at the arid end of a climate gradient
<p><span>Litter decomposition is controlled by climate, litter quality and decomposer communities. Because the decomposition of specific litter types is also influenced by the properties of adjacent types, mixing litter types may result in non-additive effects on overall decomposition rates. The strength of these effects seems to depend on the litter functional diversity. However, it is unclear which functional traits or combination of traits explain litter mixture effects and if these depend on the range of trait values and the ecosystems involved. These uncertainties hamper our ability to predict decomposition in plant communities. </span></p> <p><span>We aimed at understanding whether and how functional diversity (measured as functional dispersion, FDis) influences litter decomposition, and how this influence varies among different climates and across decomposition stages. We calculated FDis based on litter traits related to nutrient concentrations or to litter recalcitrance, and tested whether these diversity measures and climatic parameters (soil moisture and temperature) explained litter mixture effects on decomposition. </span></p> <p><span>Additive mixture effects (i.e. decomposition of mixtures equalling the mean decomposition of the single litter types) were common in most of the evaluated climates. Non-additive, negative effects were mainly restricted to the driest and warmest sites, and decreased with time. Non-additive effects increased in magnitude with the mixtures' FDis, with positive effects being related to FDis in nutrient traits and negative effects being related to FDis in recalcitrance traits. </span></p> <p><span>Synthesis: Litter mixing did not have strong effects on decomposition rates across the studied climatic gradient overall, and the direction and intensity of the mixture effects were context-dependent. The effects were stronger and more negative in the dryer ecosystems. Where effects were found, functional diversity calculated from selected groups of traits (related to nutrients or litter recalcitrance) predicted mixture effects, especially where trait ranges were broad, though much of the variation remains unexplained. We propose that functional diversity metrics based on litter traits that are mechanistically relevant, applied to diverse site-specific litter mixtures in different climates, can help to better understand under which conditions and in which direction litter diversity affects decomposition.</span></p>
Data for: Local adaptation of seed and seedling traits along a natural aridity gradient may both predict and constrain adaptive responses to climate change
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Trait functional diversity explains mixture effects on litter decomposition at the arid end of a climate gradient
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Data from: Multivariate selection mediated by aridity predicts divergence of drought resistant traits along natural aridity gradients of an invasive weed
<p><span>Geographic variation in the environment underpins selection for local adaptation and evolutionary divergence among populations. Because many environmental conditions vary across species' ranges, identifying the specific environmental variables underlying local adaptation is profoundly challenging. </span></p> <p><span>We tested whether natural selection mediated by aridity predicts clinal divergence among invasive populations of capeweed (<i><span>Arctotheca calendula</span></i>) that established and spread across southern Australia during the last two centuries. </span></p> <p><span>Using common garden experiments with two environmental treatments (wet and dry) that mimic aridity conditions across capeweed's invasive range, we estimated clinal divergence and effects of aridity on fitness and multivariate phenotypic selection in populations sampled along aridity gradients in Australia. We show that: (<i>i</i>) capeweed populations have relatively high fitness in aridity environments similar to their sampling locations; (<i>ii</i>) the magnitude and direction of selection strongly differs between wet and dry treatments, with drought stress increasing the strength of selection; and (<i>iii</i>) differences in directional selection between wet and dry treatments predict patterns of clinal divergence across the aridity gradient, particularly for traits affecting biomass, flowering phenology and putative antioxidant expression. </span></p> <p><span>Our results suggest that aridity-mediated selection contributes to trait diversification among invasive capeweed populations, possibly facilitating the expansion of capeweed across southern Australia. </span></p>
Data from: Unique drought resistance strategies occur among monkeyflower populations spanning an aridity gradient
<p>This data repository contains the metadata and data to produce all results found in the manuscript titled: "<em>Unique drought resistance strategies occur among monkeyflower populations spanning an aridity gradient</em>". This repository includes two different datasets as well as associated readme files. One dataset (fileA) contains phenotype data from an experimental manipulation experiment taking place in growth chambers at the University of Louisiana, Lafayette. The second dataset contains data from a common garden experiment that contained offspring from the well-watered treatment of the experimental manipulation from fileA. This dataset contains both offspring and midparent values for the same phenotypes measured in the experimental manipulation. Datasets are both uploaded as .csv files. Please read the readme files for descriptions of the data in each .csv file.</p>
Aridity and soil fertility, not species richness, interact to affect temporal stability along a large natural gradient in Northern China
<p><span>There is mounting evidence from experimental studies that drought and nutrient enrichment can interact to impact the biodiversity and productivity of terrestrial ecosystems. Whether such interactive effect influence plant diversity and the temporal stability of community productivity of natural ecosystems is unknown. To fill this knowledge gap, we combined a field survey of plant diversity and soil conditions with remote sensing temporal estimates of primary productivity in grasslands along a natural gradient in northern China. We found that aridity and soil ammonium (NH<sub>4</sub><sup>+</sup>-N) interacted to influence temporal stability of NDVI. That is, the relationship between ammonium and temporal stability of NDVI shifted from positive to negative due to increased </span><span>standard deviation</span> <span>of NDVI with increasing aridity. Species richness was not related to temporal stability because it influenced the mean and </span><span>standard deviation</span> <span>of NDVI proportionally. As a result, soil fertility outweighed the contribution of species richness to temporal stability. Our study demonstrates the synergistic effect of aridity and soil fertility, but not species richness, on temporal stability along a large natural gradient. Predicting how environmental drivers affect diversity and the stable provisioning of ecosystem services in real-world ecosystems therefore requires a better understanding of the complex interactions among environmental drivers.</span></p>
Data and code from: Inverse effects of soil moisture and litter quality on litter decomposition along a gradient from hyper-arid to temperate climate
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Plant defense trait responses to grazing along an aridity gradient in Inner Mongolian grasslands
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Data from: Understanding carnivore interactions in a cold arid trans-Himalayan landscape: What drives co-existence patterns within predator guild along varying resource gradients?
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Simplification of plant trait networks among communities along a climatic aridity gradient
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Aridity and soil fertility, not species richness, interact to affect temporal stability along a large natural gradient in Northern China
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Data from: Unique drought resistance strategies occur among monkeyflower populations spanning an aridity gradient
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Data from: Multivariate selection mediated by aridity predicts divergence of drought resistant traits along natural aridity gradients of an invasive weed
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Sex-specific non-structural carbohydrate variation and hydraulics explain differences in drought resistance of Populus euphratica females and males along an aridity gradient
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Data For: Soil NH3 emissions across an aridity, soil pH, and N deposition gradient in southern California
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Milkweed trait values associated with aridity gradients and drought-induced changes in hostplant quality
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Data from: Thresholds and gradients in a semi-arid grassland: long-term grazing treatments induce slow, continuous and reversible vegetation change
1. Temporal changes in semi-arid ecosystems can include transitions between alternative stable states, involving thresholds and multiple domains of attraction, but can also include relatively continuous, symmetric and reversible shifts within a single stable state. Conceptual state-and-transition models (STMs) describe both types of ecosystem dynamics by including state transitions (plant community changes difficult-to-reverse without substantial input or effort) and phase shifts (easily reversible community changes) as consequences of management practices and environmental variability. Grazing management is purported to be the primary driver of state transitions in current STMs for North American grasslands, but there is limited empirical evidence from these grasslands showing that grazing can cause difficult-to-reverse transitions between alternate stable states. 2 .In a northern mixed-grass prairie in Wyoming, USA, we examined plant community responses to (i) long-term (33-year) grazing intensity treatments (none, light, moderate and heavy stocking rates) and (ii) 8 years of light or no grazing in pastures that were grazed heavily for the previous 25 years. 3. Long-term grazing treatments were associated with distinct, but not stable, plant communities. From year 22 to 33, heavier stocking rates decreased cover of dominant C3 grasses and increased cover of the dominant C4 grass Bouteloua gracilis. 4. Reversing stocking rates from heavy to light or no grazing resulted in reversal of changes induced by prior heavy stocking for dominant C3 grasses, but not for B. gracilis. For both groups, rates of change following grazing treatment reversals were consistent with rates of change during the initial years of the experiment (1982–1990). 5. Synthesis and applications. In a semi-arid rangeland with a long evolutionary history of grazing, different long-term grazing intensity treatments caused slow, continuous, and directional changes with important management implications, but did not appear to induce alternative stable states. For this and similar ecosystems, quantifying the time-scales and compositional gradients associated with key phase shifts may be more important than identifying thresholds between alternative stable states.
Data from: Spatial and temporal aridity gradients provide poor proxies for plant-plant interactions under climate change: a large-scale experiment
1. Plant-plant interactions may critically modify the impact of climate change on plant communities. However, the magnitude and even direction of potential future interactions remains highly debated, especially for water limited ecosystems. Predictions range from increasing facilitation to increasing competition with future aridification. 2. The different methodologies used for assessing plant-plant interactions under changing environmental conditions may affect the outcome but they are not equally represented in the literature. Mechanistic experimental manipulations are rare compared to correlative approaches that infer future patterns from current observations along spatial climatic gradients. 3. Here, we utilize a unique climatic gradient in combination with a large-scale, long-term experiment to test whether predictions about plant-plant interactions yield similar results when using experimental manipulations, spatial gradients or temporal variation. We assessed shrub-annual interactions in three different sites along a natural rainfall gradient (spatial) during 9 years of varying rainfall (temporal) and 8 years of dry and wet manipulations of ambient rainfall (experimental) that closely mimicked regional climate scenarios. 4. The results were fundamentally different among all three approaches. Experimental water manipulations hardly altered shrub effects on annual plant communities for the assessed fitness parameters biomass and survival. Along the spatial gradient, shrub effects shifted from clearly negative to mildly facilitative towards drier sites, whereas temporal variation showed the opposite trend: more negative shrub effects in drier years. 5. Based on our experimental approach, we conclude that shrub-annual interaction will remain similar under climate change. In contrast, the commonly applied space-for time approach based on spatial gradients would have suggested increasing facilitative effects with climate change. We discuss potential mechanisms governing the differences among the three approaches. 6. Our study highlights the critical importance of long-term experimental manipulations for evaluating climate change impacts. Correlative approaches, e.g. along spatial or temporal gradients, may be misleading and overestimate the response of plant-plant interactions to climate change.
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Allen Brain Atlas
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