Spatially explicit null models in biogeography: Toward a multi-scale understanding of the niche.

In general, most ecologists envision the niche as a central organizing tenet, and that particular parameters of the niche help structure biogeographic patterns of diversity, distribution and abundance. The major emergent alternative to the niche concept requires the inference of background stochasticity, and its application through null models. For example, rather than competitive interactions of species shaping the coexistence of species, historical accidents of dispersal have been suggested. In this thesis I explore, in some detail, the concept of niche using of null models. In this thesis, two detailed and quite different null models are presented. The first, based on the Mid-Domain Effect (MDE), explores the influence of continental geometry on patterns in species richness and range size frequency distributions. I compared the MDE predictions first to observations on tree species richness in continental North America (n = 417 species), and then to amphibian, bird and mammal species richness across North and South America (n = 2216, 3771 and 1605 species, respectively) contrasting the relative contributions of null model results and environmental correlates. I have developed a novel null methodology to predict the niche of a species, or a group of species; I applied this at local and regional scales to examine null spatial distribution predictions for a single, endangered species at the local scale ( Opuntia humifusa at Point Pelee National Park), and for groups of rare species at a regional scale (based on reported occurrences across south-western Ontario). Results can be regarded as representing intermediate states between the extremes of continua of which niche and neutral models form the ends. With respect to the relative strengths of stochastic and deterministic processes, this thesis has characterized the attributes of groups of species. For example, large-ranged NA tree species are influenced by the MDE more than small-ranged species; moreover, regional, null species distribution models performed best for birds, insects, reptiles, sedges, as well as for aquatic and terrestrial plants. It seems most likely that real species distributions are the product of variation in relative strength of stochastic and deterministic processes.Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2006 .V36. Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3559. Thesis (Ph.D.)--University of Windsor (Canada), 2006

Alfalfa water productivity and yield gaps in the U.S. central Great Plains

Context: Yield gap (Yg) analyses using farmer-reported yield and management data have been performed for a number of annual grain crops, but it lacks for perennial forages. The U.S. accounts for 21 % of the global alfalfa production with a large rainfed area located in the central Great Plains, serving as an interesting case-study for Yg in perennial forages. Most existing alfalfa Yg analyses quantified the magnitude of the Yg but failed to identify associated management practices to reduce it. Challenging this analysis, a systematic benchmark for alfalfa water productivity [WP, kg dry matter per mm evapotranspiration (ETc)] that allows for the quantification of Yg in farmer fields does not exist. Objectives: Our objectives were to (i) benchmark alfalfa WP, (ii) quantify Yg in alfalfa farmer fields, and (iii) identify management opportunities to improve alfalfa yield. Methods: We conducted a systematic review of literature and compiled a database on alfalfa yield and ETc (n = 68 papers and 1027 treatment means) from which a WP boundary function was derived. We collected management and yield data from 394 commercial rainfed alfalfa fields during 2016–2019 in central Kansas. We then used satellite imagery to define the growing season (and corresponding water supply) for each field. The boundary function was then used to calculate Yg of each field, and conditional inference trees (CIT) explored the impact of management practices associated with increased yield. Results: Our boundary function suggested an alfalfa WP of 34 kg ha-1 mm-1. Farmer-reported yield ranged from 0.9 to 19.0 Mg ha-1, averaging 7.6 Mg ha-1. Alfalfa water-limited yield potential (Yw) ranged from 11.1 to 23.2 Mg ha-1, resulting in an average yield gap of 54–60 % of Yw. Row spacing, seeding rates, and management of phosphorus fertilizer were major agronomic practices explaining alfalfa yields in farmer fields, followed by surrogate variables as sowing season, stand age, and soil pH. Conclusions: Our study provided the first systematic analysis estimating attainable alfalfa WP as function of ETc, suggesting that large alfalfa Yg exist in the U.S. central Great Plains. We also identified key agronomic practices associated with increased alfalfa yield. Significance: The WP here derived can be used for future studies aiming at quantifying alfalfa Yg across the globe. This was an initial step in quantifying Yg and its associated causes at farmer fields, and we highlight limitations and future directions for perennial forages yield gap analyses

The Power of Expert Opinion in Ecological Models Using Bayesian Methods: Impact of Grazing on Birds

One of our greatest challenges as researchers is predicting impacts of landuse on biota and predicting the impact of livestock grazing on birds is no exception. Insufficient data and poor survey design often yield results that are not statistically significant or difficult to interpret because researchers cannot disentangle the effects of grazing from other disturbances. This has resulted in few publications on the impact of grazing on birds alone. Ecologists with extensive experience in bird ecology in grazed landscapes could inform an analysis when time and monetary constraints limit the amount of data that can be collected. Using responses from twenty well-recognised ecologists throughout Australia we capture this expert knowledge and incorporate it into a statistical model using Bayesian methods. Although relatively new to ecology, Bayesian methods allow straightforward probability statements to be made about specific models or scenarios and they allow the integration of different types of information, including scientific judgement while formally accommodating and incorporating the uncertainty in the information provided. Data on bird density was collected across three broad levels of grazing (no/low, moderate and high) typical of sub-tropical Australia. This field data was used in conjunction with expert data to produce estimates of species persistence under grazing. The addition of expert data through priors in our model strengthened results under at least one grazing level for all but one bird species examined. When experts were in agreement credible intervals were tightened substantially, whereas when experts were in disagreement results were similar to those evaluated in the absence of expert information. In fields where there is extensive expert knowledge, yet little published data, the use of expert information as priors for ecological models is a cost effective way of making more confident predictions about the effect of management on biodiversity

A Survey of Procedural Techniques for City Generation

The computer game industry requires a skilled workforce and this combined with the complexity of modern games, means that production costs are extremely high. One of the most time consuming aspects is the creation of game geometry, the virtual world which the players inhabit. Procedural techniques have been used within computer graphics to create natural textures, simulate special effects and generate complex natural models including trees and waterfalls. It is these procedural techniques that we intend to harness to generate geometry and textures suitable for a game situated in an urban environment. Procedural techniques can provide many benefits for computer graphics applications when the correct algorithm is used. An overview of several commonly used procedural techniques including fractals, L-systems, Perlin noise, tiling systems and cellular basis is provided. The function of each technique and the resulting output they create are discussed to better understand their characteristics, benefits and relevance to the city generation problem. City generation is the creation of an urban area which necessitates the creation of buildings, situated along streets and arranged in appropriate patterns. Some research has already taken place into recreating road network patterns and generating buildings that can vary in function and architectural style. We will study the main body of existing research into procedural city generation and provide an overview of their implementations and a critique of their functionality and results. Finally we present areas in which further research into the generation of cities is required and outline our research goals for city generation

Proseduraalisen tietomallintamisen käyttöönotto kaupunkisuunnittelussa

This thesis examines procedural modeling as a tool for urban plan creation. Procedural modeling historically has been used for 3D visualization of natural features, but with the release of the soft-ware CityEngine in 2008 the technology can easily be adopted also in problem domains dealing with urban environments. The study begins with a requirement analysis conducted to explore the needs urban planning imposes on the technology, based on which a functional procedural modeling production system is built using the CityEngine platform and its Computer Generated Architecture (CGA) scripting language. A solution is presented to the problem of control in procedural generation methods by introducing the concept of a selectable “Level of Control” and how its implementation in the produced system enables the planner to flexibly assume the necessary amount of control over the generated model. The finished product is then compared against the presented requirements of accuracy, efficiency, ease of use, high visual qualities, and advanced analytical capabilities. The efficiency of the system measured as the ratio between user interactions (mouse clicks and keystrokes) and modeling output in the setting of the assessment is found out to be two to three times greater than the efficiency of a more established manual modeling software. The technology as demonstrated through the produced system is concluded to be especially suitable for preliminary land use studies estimating the building potentials of extensive land areas. Directions for future research with potential to expand the applicability of the technology are discussed.Tässä diplomityössä tutkitaan proseduraalista mallintamista kaupunkisuunnittelun työvälineenä. Proseduraalista mallintamista on historiallisesti käytetty luonnonmuotojen 3D-visualisoimiseen, mutta vuonna 2008 julkaistu CityEngine-ohjelma mahdollistaa teknologian helpon käyttöönoton myös rakennettua ympäristöä koskevissa aihepiireissä. Tutkielma alkaa analyysillä kaupunkisuunnittelun teknologiaan kohdistamista vaatimuksista, joiden perusteella rakennetaan CityEngineen ja sen Computer Generated Architecture (CGA) ohjel-mointikieleen perustuva proseduraalinen mallinnusjärjestelmä. Ratkaisuna proseduraaliseen mallintamiseen liittyvään kontrollin problematiikkaan esitellään käsite valittavasta ”kontrollitasosta”, ja kuinka sen implementaatio toteutetussa järjestelmässä mahdollistaa suunnittelijan ottaa joustavasti tarpeellisen määrän kontrollia generoitavan mallin suhteen. Valmista tuotetta verrataan esitettyihin tarkkuuden, tehokkuuden, käytön helppouden, korkealaatuisen visuaalisuuden, sekä kehittyneen analytiikan vaatimuksiin. Järjestelmän tehokkuus mitattuna käyttäjäinteraktioiden (hiiren klikkaukset ja näppäimistön painallukset) ja tuotetun mallin suhteena mittauksen asetelmassa on kahdesta kolmeen kertaa suurempi kuin vakiintuneemman manuaalisen mallinnusohjelman tehokkuus. Proseduraalisen mallintamisen, sellaisena kuin se tuotetussa järjestelmässä on implementoitu, todetaan olevan erityisen sopiva alustavien rakentamisen määrää laajoille alueille haarukoivien maankäyttötarkastelujen tuottamiseen. Työn lopuksi käsitellään teknologian käyttöaluetta laajentavia tutkimussuuntia

Land systems as surrogates for biodiversity in conservation planning

Environmental surrogates (land classes) for the distribution of biodiversity are increasingly being used for conservation planning. However; data that demonstrate coincident patterns in land classes and biodiversity are limited. We ask the overall question, "Are land systems effective surrogates for the spatial configuration of biodiversity for conservation planning?" and we address three specific questions: (1) Do different land systems represent different biological assemblages.? (2) Do biological assemblages on the same land system remain similar with increasing geographic separation? and (3) Do biological assemblages on the same land system remain similar with increasing land system isolation? Vascular plants, invertebrates, and microbiota were surveyed from 24 sites in four land systems in and northwest New South Wales, Australia. Within each land system, sites were located to give a hierarchy of inter-site distances, and land systems were classified as either "low isolation" (large and continuous) or "high isolation" (small patches interspersed among other land systems). Each type of land system supported components of biodiversity either not found, or found infrequently, on other land systems, suggesting that land systems function as surrogates for biodiversity, and that conservation-area networks representing land-system diversity will also represent biological diversity. However, the majority of taxa were found on more than one land-system type, suggesting that a large proportion of the plant, arthropod, and microbial biodiversity may be characterized by widespread species with low fidelity to particular land systems. Significant relationships between geographic distance among sites and differences among assemblages were revealed for all taxa except the microbiota. Therefore, as sites on the same land system were located farther apart, the assemblages at those sites became more different. This finding strongly suggests that conservation planning based on land-system diversity should also sample the geographic range occupied by each land system. Land-system isolation was not revealed to be a significant Source of variation in assemblage composition. Our research finds support for environmental surrogates for biodiversity in conservation planning, specifically the use of land systems and similarly derived land classifications. However, the need for explicit modeling of geographic distance in conservation planning is clearly indicated