Statistical Invariance of Betti Numbers in the Thermodynamic Regime

Topological Data Analysis (TDA) has become a promising tool to uncover low-dimensional features from high-dimensional data. Notwithstanding the advantages afforded by TDA, its adoption in statistical methodology has been limited by several reasons. In this paper we study the framework of topological inference through the lens of classical parametric inference in statistics. Suppose $\mathcal{P} = \{\mathbb{P}_\theta : \theta \in \Theta\}$ is a parametric family of distributions indexed by a set $\Theta$, and $\mathbb{X}_n = \{\mathbf{X}_1, \mathbf{X}_2, \dots, \mathbf{X}_n\}$ is observed iid at random from a distribution $\mathbb{P}_\theta$. The asymptotic behaviour of the Betti numbers associated with the \v{C}ech complex of $\mathbb{X}_n$ contain both the topological and parametric information about the distribution of points. We investigate necessary and sufficient conditions under which topological inference is possible in this parametric setup

Nutrient addition increases grassland sensitivity to droughts

Grasslands worldwide are expected to experience an increase in extreme events such asdrought, along with simultaneous increases in mineral nutrient inputs as a result of human industrialactivities. These changes are likely to interact because elevated nutrient inputs may alter plantdiversity and increase the sensitivity to droughts. Dividing a system?s sensitivity to drought intoresistance to change during the drought and rate of recovery after the drought generates insights intodifferent dimensions of the system?s resilience in the face of drought. Here, we examine the effects ofexperimental nutrient fertilization and the resulting diversity loss on the resistance to and recoveryfrom severe regional droughts. We do this at 13 North American sites spanning gradients of aridity, 5annual grasslands in California and 8 perennial grasslands in the Great Plains. We measured rate ofresistance as the change in annual aboveground biomass (ANPP) per unit change in growing seasonprecipitation as conditions declined from normal to drought. We measured recovery as the change inANPP during the post drought period and the return to normal precipitation. Resistance and recoverydid not vary across the 400 mm range of mean growing season precipitation spanned by our sites inthe Great Plains. However, chronic nutrient fertilization in the Great Plains reduced drought resistanceand increased drought recovery. In the California annual grasslands, arid sites had a greater recoverypost-drought than mesic sites, and nutrient addition had no consistent effects on resistance orrecovery. Across all study sites, we found that pre-drought species richness in natural grasslands wasnot consistently associated with rates of resistance to or recovery from the drought, in contrast toearlier findings from experimentally assembled grassland communities. Taken together, these resultssuggest that human-induced eutrophication may destabilize grassland primary production, but theeffects of this may vary across regions and flora, especially between perennial and annual-dominatedgrasslands.Fil: Bharath, Siddharth. University of Minnesota; Estados UnidosFil: Borer, Elizabeth. University of Minnesota; Estados UnidosFil: Biederman, Lori A.. owa State University; Estados UnidosFil: Blumenthal, Dana M.. State University of Colorado - Fort Collins; Estados UnidosFil: Fay, Philip A.. United States Department of Agriculture; Estados UnidosFil: Gherardi, Laureano. Arizona State University; Estados UnidosFil: Knops, Johannes M. H.. United States Department of Agriculture; Estados UnidosFil: Leakey, Andrew D. B.. State University of Colorado - Fort Collins; Estados UnidosFil: Yahdjian, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Seabloom, Eric. University of Minnesota; Estados Unido

Linking changes in species composition and biomass in a globally distributed grassland experiment

Global change drivers, such as anthropogenic nutrient inputs, are increasing globally. Nutrient deposition simultaneously alters plant biodiversity, species composition and ecosystem processes like aboveground biomass production. These changes are underpinned by species extinction, colonisation and shifting relative abundance. Here, we use the Price equation to quantify and link the contributions of species that are lost, gained or that persist to change in aboveground biomass in 59 experimental grassland sites. Under ambient (control) conditions, compositional and biomass turnover was high, and losses (i.e. local extinctions) were balanced by gains (i.e. colonisation). Under fertilisation, the decline in species richness resulted from increased species loss and decreases in species gained. Biomass increase under fertilisation resulted mostly from species that persist and to a lesser extent from species gained. Drivers of ecological change can interact relatively independently with diversity, composition and ecosystem processes and functions such as aboveground biomass due to the individual contributions of species lost, gained or persisting.EEA Santa CruzFil: Ladouceur, Emma. German Centre for Integrative Biodiversity Research (iDiv); AlemaniaFil: Ladouceur, Emma. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; AlemaniaFil: Ladouceur, Emma. University of Leipzig. Department of Biology; AlemaniaFil: Ladouceur, Emma. Martin Luther University Halle-Wittenberg. Institute of Computer Science; AlemaniaFil: Blowes, Shane A. German Centre for Integrative Biodiversity Research (iDiv); AlemaniaFil: Blowes, Shane A. Martin Luther University Halle-Wittenberg. Institute of Computer Science; AlemaniaFil: Chase, Jonathan M. German Centre for Integrative Biodiversity Research (iDiv); AlemaniaFil: Chase, Jonathan M. Martin Luther University Halle-Wittenberg. Institute of Computer Science; AlemaniaFil: Clark, Adam T. German Centre for Integrative Biodiversity Research (iDiv); AlemaniaFil: Clark, Adam T. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; AlemaniaFil: Clark, Adam T. Karl-Franzens University of Graz. Institute of Biology; Austria.Fil: Garbowski, Magda. German Centre for Integrative Biodiversity Research (iDiv); AlemaniaFil: Garbowski, Magda. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; AlemaniaFil: Alberti, Juan. Universidad Nacional de Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Laboratorio de Ecología. Mar del Plata; Argentina.Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Arnillas, Carlos Alberto. University of Toronto. Department of Physical and Environmental Sciences; Canadá.Fil: Bakker, Jonathan D. University of Washington. School of Environmental and Forest Sciences; Estados UnidosFil: Barrio, Isabel C. Agricultural University of Iceland. Faculty of Environmental and Forest Sciences; IslandiaFil: Bharath, Siddharth. Atria University; India.Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina.Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina.Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Harpole, Stanley. German Centre for Integrative Biodiversity Research (iDiv); AlemaniaFil: Harpole, Stanley. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; AlemaniaMartin Luther University Halle-Wittenberg. Institute of Computer Science; Alemani

Linking changes in species composition and biomass in a globally distributed grassland experiment

Global change drivers, such as anthropogenic nutrient inputs, are increasing globally. Nutrient deposition simultaneously alters plant biodiversity, species composition and ecosystem processes like aboveground biomass production. These changes are underpinned by species extinction, colonisation and shifting relative abundance. Here, we use the Price equation to quantify and link the contributions of species that are lost, gained or that persist to change in aboveground biomass in 59 experimental grassland sites. Under ambient (control) conditions, compositional and biomass turnover was high, and losses (i.e. local extinctions) were balanced by gains (i.e. colonisation). Under fertilisation, the decline in species richness resulted from increased species loss and decreases in species gained. Biomass increase under fertilisation resulted mostly from species that persist and to a lesser extent from species gained. Drivers of ecological change can interact relatively independently with diversity, composition and ecosystem processes and functions such as aboveground biomass due to the individual contributions of species lost, gained or persisting.Fil: Ladouceur, Emma. Martin Luther University Halle-Wittenberg; Alemania. Universitat Leipzig; Alemania. German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena; AlemaniaFil: Blowes, Shane A.. Martin Luther University Halle-Wittenberg; Alemania. German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena; AlemaniaFil: Chase, Jonathan M.. German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena; Alemania. Martin Luther University Halle-Wittenberg; AlemaniaFil: Clark, Adam T.. Martin Luther University Halle-Wittenberg; Alemania. German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena; Alemania. University of Graz; AustriaFil: Garbowski, Magda. German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena; Alemania. Universitat Leipzig; AlemaniaFil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Arnillas, Carlos Alberto. University of Toronto; CanadáFil: Bakker, Jonathan. University of Washington; Estados UnidosFil: Barrio, Isabel C.. Agricultural University of Iceland; IslandiaFil: Bharath, Siddharth. Atria University; IndiaFil: Borer, Elizabeth. University of Minnesota; Estados UnidosFil: Brudvig, Lars A.. Michigan State University; Estados UnidosFil: Cadotte, Marc W.. University of Toronto; CanadáFil: Chen, Qingqing. Peking University; ChinaFil: Collins, Scott L.. University of New Mexico; Estados UnidosFil: Dickman, Christopher R.. The University Of Sydney; AustraliaFil: Donohue, Ian. Trinity College Dublin; IrlandaFil: Du, Guozhen. Lanzhou University; ChinaFil: Ebeling, Anne. Universitat Jena; AlemaniaFil: Eisenhauer, Nico. Martin Luther University Halle—Wittenberg; Alemania. German Centre For Integrative Biodiversity Research (idiv) Halle-jena-leipzig; AlemaniaFil: Fay, Philip A.. USDA-ARS Grassland Soil and Water Research Lab; Estados UnidosFil: Hagenah, Nicole. University Of Pretoria; SudáfricaFil: Hautier, Yann. University of Utrecht; Países BajosFil: Jentsch, Anke. University of Bayreuth; AlemaniaFil: Jónsdóttir, Ingibjörg S.. University of Iceland; IslandiaFil: Komatsu, Kimberly J.. Smithsonian Environmental Research Center; Estados UnidosFil: MacDougall, Andrew. University of Guelph; CanadáFil: Martina, Jason P.. Texas State University; Estados UnidosFil: Moore, Joslin L.. Arthur Rylah Institute For Environmental Research; Australia. Monash University; AustraliaFil: Morgan, John W.. La Trobe University; AustraliaFil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Multiple resource limitations explain biomass-precipitation relationships in grasslands

Interannual variability in grassland primary production is strongly driven by precipitation, nutrient availability and herbivory, but there is no general consensus on the mechanisms linking these variables. If grassland biomass is limited by the single most limiting resource at a given time, then we expect that nutrient addition will not affect biomass production at arid sites. We conducted a distributed experiment manipulating nutrients and herbivores at 44 grassland sites in 8 regions around the world, spanning a broad range in aridity. We estimated the effects of 5-11 years of nutrient addition and herbivore exclusion treatments on precipitation sensitivity of biomass (proportional change in biomass relative to proportional change in rainfall among years), and the biomass in the driest year (to measure treatment effects when water was most limiting) at each site. Grazer exclusion did not interact with nutrients to influence driest year biomass or sensitivity. Nutrient addition increased driest year biomass by 74% and sensitivity by 0.12 (proportional units), and that effect did not change across the range of aridity spanned by our sites. Grazer exclusion did not interact with nutrients to influence sensitivity or driest year biomass. At almost half of our sites, the previous year\u27s rainfall explained as much variation in biomass as current year precipitation. Overall, our distributed fertilization experiment detected co-limitation between nutrients and water governing grasslands, with biomass sensitivity to precipitation being limited by nutrient availability irrespective of site aridity and herbivory. Our findings refute the classical ideas that grassland plant performance is limited by the single most limiting resource at a site. This suggests that nutrient eutrophication will destabilize grassland ecosystems through increased sensitivity to precipitation variation

Daksha: On Alert for High Energy Transients

We present Daksha, a proposed high energy transients mission for the study of electromagnetic counterparts of gravitational wave sources, and gamma ray bursts. Daksha will comprise of two satellites in low earth equatorial orbits, on opposite sides of earth. Each satellite will carry three types of detectors to cover the entire sky in an energy range from 1 keV to >1 MeV. Any transients detected on-board will be announced publicly within minutes of discovery. All photon data will be downloaded in ground station passes to obtain source positions, spectra, and light curves. In addition, Daksha will address a wide range of science cases including monitoring X-ray pulsars, studies of magnetars, solar flares, searches for fast radio burst counterparts, routine monitoring of bright persistent high energy sources, terrestrial gamma-ray flashes, and probing primordial black hole abundances through lensing. In this paper, we discuss the technical capabilities of Daksha, while the detailed science case is discussed in a separate paper.Comment: 9 pages, 3 figures, 1 table. Additional information about the mission is available at https://www.dakshasat.in

Science with the Daksha High Energy Transients Mission

We present the science case for the proposed Daksha high energy transients mission. Daksha will comprise of two satellites covering the entire sky from 1~keV to $>1$~MeV. The primary objectives of the mission are to discover and characterize electromagnetic counterparts to gravitational wave source; and to study Gamma Ray Bursts (GRBs). Daksha is a versatile all-sky monitor that can address a wide variety of science cases. With its broadband spectral response, high sensitivity, and continuous all-sky coverage, it will discover fainter and rarer sources than any other existing or proposed mission. Daksha can make key strides in GRB research with polarization studies, prompt soft spectroscopy, and fine time-resolved spectral studies. Daksha will provide continuous monitoring of X-ray pulsars. It will detect magnetar outbursts and high energy counterparts to Fast Radio Bursts. Using Earth occultation to measure source fluxes, the two satellites together will obtain daily flux measurements of bright hard X-ray sources including active galactic nuclei, X-ray binaries, and slow transients like Novae. Correlation studies between the two satellites can be used to probe primordial black holes through lensing. Daksha will have a set of detectors continuously pointing towards the Sun, providing excellent hard X-ray monitoring data. Closer to home, the high sensitivity and time resolution of Daksha can be leveraged for the characterization of Terrestrial Gamma-ray Flashes.Comment: 19 pages, 7 figures. Submitted to ApJ. More details about the mission at https://www.dakshasat.in

A dominant dwarf shrub increases diversity of herbaceous plant communities in a Trans-Himalayan rangeland

Plant communities are structured by both competition and facilitation. The interplay between the two interactions can vary depending on environmental factors, nature of stress, and plant traits. But, whether positive or negative interactions dominate in regions of high biotic and abiotic stress remains unclear.We studied herbaceous plant communities associated with a dwarf shrub Caragana versicolor in semi-arid, high altitude Trans Himalayan rangelands of Spiti, India. We surveyed 120 pairs of plots (within and outside shrub canopies) across four watersheds differing in altitude, aspect and dominant herbivores. Herbaceous communities within shrub canopies had 25% higher species richness, but similar abundance when compared to communities outside the canopy, with the shrub edge having higher diversity than the center of the canopy. Grasses and erect forbs showed positive associations with the shrub, while prostrate plants occurred at much lower abundance within the canopy. Rare species showed stronger positive associations with Caragana than abundant species. Experimental removal of herbaceous vegetation from within shrub canopies led to 42% increase in flowering in Caragana, indicating a cost to the host shrubs. Our study indicates a robust pattern of a dwarf shrub facilitating local community diversity across this alpine landscape, increasing diversity at the plot level, facilitating rare species, and yet incurring a cost to hosts from the presence of herbaceous plants. Given these large influences of this shrub on vegetation of these high altitude rangelands, we suggest that the shrub microhabitat be explicitly considered in any analyses of ecosystem health in such rangelands

Linking changes in species composition and biomass in a globally distributed grassland experiment

Global change drivers, such as anthropogenic nutrient inputs, are increasing globally. Nutrient deposition simultaneously alters plant biodiversity, species composition and ecosystem processes like aboveground biomass production. These changes are underpinned by species extinction, colonisation and shifting relative abundance. Here, we use the Price equation to quantify and link the contributions of species that are lost, gained or that persist to change in aboveground biomass in 59 experimental grassland sites. Under ambient (control) conditions, compositional and biomass turnover was high, and losses (i.e. local extinctions) were balanced by gains (i.e. colonisation). Under fertilisation, the decline in species richness resulted from increased species loss and decreases in species gained. Biomass increase under fertilisation resulted mostly from species that persist and to a lesser extent from species gained. Drivers of ecological change can interact relatively independently with diversity, composition and ecosystem processes and functions such as aboveground biomass due to the individual contributions of species lost, gained or persisting

Sensitivity of grasslands to rainfall variation: the role of resource colimitation

University of Minnesota Ph.D. dissertation. August 2020. Major: Ecology, Evolution and Behavior. Advisors: Elizabeth Borer, Eric Seabloom. 1 computer file (PDF); ix, 94 pages.Identifying the factors shaping ecosystem sensitivity to global change is an important unresolved question in ecology. Grasslands and savannas account for one-third of Earth's terrestrial primary production, and variation in that production is strongly driven by rainfall. The sensitivity of ecosystems to rainfall should depend on the availability of other co-limiting resources, such as nutrients. However, it is unclear how the strength of that co-limitation varies among sites - across gradients of aridity, soil fertility and community composition. I leverage long term experiments within the Nutrient Network research cooperative to analyse how fertilization affects the sensitivity of grassland plant communities to rainfall. I expected that sensitivity to rainfall would decline from arid to mesic ecosystems, while the effects of fertilization on sensitivity would increase along that same gradient. I found the sensitivity of grasslands to extreme drought in 13 sites did not change with aridity, but it was increased by fertilization. For 37 grassland sites around the world, fertilization generally increased the sensitivity of biomass to rainfall variation irrespective of aridity. This showed that grasslands are co-limited by nutrients and water all across the aridity gradient present among our sites. Finally, I found that community shifts due to chronic nutrient addition at more than half the sites studied will still retain species that perform well in both high and low rainfall years. Thus composition change is unlikely to amplify the effects of nutrient addition on biomass sensitivity to precipitation