The Experts below are selected from a list of 10263 Experts worldwide ranked by ideXlab platform
Thomas W Gillespie - One of the best experts on this subject based on the ideXlab platform.
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global tropical dry forest extent and cover a comparative study of bioclimatic definitions using two climatic data sets
PLOS ONE, 2021Co-Authors: Jonathan Pando Ocon, Thomas Ibanez, Janet Franklin, Stephanie Pau, Gunnar Keppel, Gonzalo Rivastorres, Michael Edward Shin, Thomas W GillespieAbstract:There is a debate concerning the definition and extent of tropical dry forest biome and vegetation type at a global spatial scale. We identify the potential extent of the tropical dry forest biome based on bioclimatic definitions and climatic data sets to improve global estimates of distribution, cover, and change. We compared four bioclimatic definitions of the tropical dry forest biome–Murphy and Lugo, Food and Agriculture Organization (FAO), DryFlor, aridity index–using two climatic data sets: WorldClim and Climatologies at High-resolution for the Earth’s Land Surface Areas (CHELSA). We then compared each of the eight unique combinations of bioclimatic definitions and climatic data sets using 540 field plots identified as tropical dry forest from a literature search and evaluated the accuracy of World Wildlife Fund tropical and subtropical dry broadleaf forest Ecoregions. We used the definition and climate data that most closely matched field data to calculate forest cover in 2000 and change from 2001 to 2020. Globally, there was low agreement (< 58%) between bioclimatic definitions and WWF Ecoregions and only 40% of field plots fell within these Ecoregions. FAO using CHELSA had the highest agreement with field plots (81%) and was not correlated with the biome extent. Using the FAO definition with CHELSA climatic data set, we estimate 4,931,414 km 2 of closed canopy (≥ 40% forest cover) tropical dry forest in 2000 and 4,369,695 km 2 in 2020 with a gross loss of 561,719 km 2 (11.4%) from 2001 to 2020. Tropical dry forest biome extent varies significantly based on bioclimatic definition used, with nearly half of all tropical dry forest vegetation missed when using Ecoregion boundaries alone, especially in Africa. Using site-specific field validation, we find that the FAO definition using CHELSA provides an accurate, standard, and repeatable way to assess tropical dry forest cover and change at a global scale.
Silke Werth - One of the best experts on this subject based on the ideXlab platform.
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ecological specialization in trebouxia trebouxiophyceae photobionts of ramalina menziesii ramalinaceae across six range covering Ecoregions of western north america
American Journal of Botany, 2014Co-Authors: Silke Werth, Victoria L SorkAbstract: Premise of the study: Many lichens exhibit extensive ranges spanning several Ecoregions. It has been hypothesized that this wide ecological amplitude is facilitated by fungal association with locally adapted photobiont strains. Methods: We studied the identity and geographic distribution of photobionts of the widely distributed North American lichen Ramalina menziesii based on rbcL (chloroplast DNA) and nuclear ribosomal ITS DNA sequences. To test for ecological specialization, we associate photobiont genotypes with local climate and phorophyte. Key results: Of the photobiont lineages of R. menziesii , 94% belong to a clade including Trebouxia decolorans. The remaining are related to T. jamesii . The photobionts showed (1) signifi cant structure according to Ecoregion and phorophyte species and (2) genetic associations with phorophyte species and climate. Conclusions: Geography, climate, and ecological specialization shape genetic differentiation of lichen photobionts. One great advantage of independent dispersal of the fungus is symbiotic association with locally adapted photobiont strains.
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phylogeography of ramalina menziesii a widely distributed lichen forming fungus in western north america
Molecular Ecology, 2014Co-Authors: Victoria L Sork, Silke WerthAbstract:The complex topography and climate history of western North America offer a setting where lineage formation, accumulation and migration have led to elevated inter- and intraspecific biodiversity in many taxa. Here, we study Ramalina menziesii, an epiphytic lichenized fungus with a range encompassing major ecosystems from Baja California to Alaska to explore the predictions of two hypotheses: (i) that the widespread distribution of R. menziesii is due to a single migration episode from a single lineage and (ii) that the widespread distribution is due to the formation and persistence of multiple lineages structured throughout the species' range. To obtain evidence for these predictions, we first construct a phylogenetic tree and identify multiple lineages structured throughout the species' range – some ancient ones that are localized and other more recent lineages that are widely distributed. Second, we use an isolation with migration model to show that sets of Ecoregion populations diverged from each other at different times, demonstrating the importance of historical and current barriers to gene flow. Third, we estimated migration rates among Ecoregions and find that Baja California populations are relatively isolated, that inland California Ecoregion populations do not send out emigrants and that migration out of California coastal and Pacific Northwest populations into inland California Ecoregions is high. Such intraspecific geographical patterns of population persistence and dispersal both contribute to the wide range of this genetically diverse lichen fungus and provide insight into the evolutionary processes that enhance species diversity of the California Floristic Province.
Glenn E. Griffith - One of the best experts on this subject based on the ideXlab platform.
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Ecoregions of the Conterminous United States: Evolution of a Hierarchical Spatial Framework
Environmental Management, 2014Co-Authors: James M. Omernik, Glenn E. GriffithAbstract:A map of ecological regions of the conterminous United States, first published in 1987, has been greatly refined and expanded into a hierarchical spatial framework in response to user needs, particularly by state resource management agencies. In collaboration with scientists and resource managers from numerous agencies and institutions in the United States, Mexico, and Canada, the framework has been expanded to cover North America, and the original Ecoregions (now termed Level III) have been refined, subdivided, and aggregated to identify coarser as well as more detailed spatial units. The most generalized units (Level I) define 10 Ecoregions in the conterminous U.S., while the finest-scale units (Level IV) identify 967 Ecoregions. In this paper, we explain the logic underpinning the approach, discuss the evolution of the regional mapping process, and provide examples of how the Ecoregions were distinguished at each hierarchical level. The variety of applications of the Ecoregion framework illustrates its utility in resource assessment and management.
Jonathan Pando Ocon - One of the best experts on this subject based on the ideXlab platform.
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global tropical dry forest extent and cover a comparative study of bioclimatic definitions using two climatic data sets
PLOS ONE, 2021Co-Authors: Jonathan Pando Ocon, Thomas Ibanez, Janet Franklin, Stephanie Pau, Gunnar Keppel, Gonzalo Rivastorres, Michael Edward Shin, Thomas W GillespieAbstract:There is a debate concerning the definition and extent of tropical dry forest biome and vegetation type at a global spatial scale. We identify the potential extent of the tropical dry forest biome based on bioclimatic definitions and climatic data sets to improve global estimates of distribution, cover, and change. We compared four bioclimatic definitions of the tropical dry forest biome–Murphy and Lugo, Food and Agriculture Organization (FAO), DryFlor, aridity index–using two climatic data sets: WorldClim and Climatologies at High-resolution for the Earth’s Land Surface Areas (CHELSA). We then compared each of the eight unique combinations of bioclimatic definitions and climatic data sets using 540 field plots identified as tropical dry forest from a literature search and evaluated the accuracy of World Wildlife Fund tropical and subtropical dry broadleaf forest Ecoregions. We used the definition and climate data that most closely matched field data to calculate forest cover in 2000 and change from 2001 to 2020. Globally, there was low agreement (< 58%) between bioclimatic definitions and WWF Ecoregions and only 40% of field plots fell within these Ecoregions. FAO using CHELSA had the highest agreement with field plots (81%) and was not correlated with the biome extent. Using the FAO definition with CHELSA climatic data set, we estimate 4,931,414 km 2 of closed canopy (≥ 40% forest cover) tropical dry forest in 2000 and 4,369,695 km 2 in 2020 with a gross loss of 561,719 km 2 (11.4%) from 2001 to 2020. Tropical dry forest biome extent varies significantly based on bioclimatic definition used, with nearly half of all tropical dry forest vegetation missed when using Ecoregion boundaries alone, especially in Africa. Using site-specific field validation, we find that the FAO definition using CHELSA provides an accurate, standard, and repeatable way to assess tropical dry forest cover and change at a global scale.
Markus Diekmann - One of the best experts on this subject based on the ideXlab platform.
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lake depth and geographical position modify lake fish assemblages of the european central plains Ecoregion
Freshwater Biology, 2007Co-Authors: Thomas Mehner, Kerstin Holmgren, Torben L Lauridsen, Erik Jeppesen, Markus DiekmannAbstract:Summary 1. Classification of European lake fish assemblages can be based on fish-assemblage structure or morphological, geographical, physical and chemical lake attributes. However, substantial gaps in knowledge exist with respect to the correspondence between both classification approaches. 2. Here, we compiled fish assemblage data from 165 lakes situated in the European ‘Central Plains’ Ecoregion. Cluster analysis of fish abundances was performed to compare fish assemblage types of the entire Ecoregion with those from previous country-specific studies. Nonparametric group comparisons, classification trees and partial canonical ordinations were used to infer the correspondence between fish assemblage types and morphology, geographical position and nutrient concentration of the lakes. 3. Three distinct fish assemblages were revealed: vendace (Coregonus albula), ruffe (Gymnocephalus cernuus) and roach (Rutilus rutilus) lake types. Both latitude and lake depth were the best determinants of lake type, but total phosphorus (TP) concentrations were also important. Vendace lakes were deep and had low TP concentrations, whereas the shallower ruffe and roach lakes had higher TP values. Roach lakes were more frequent in the north-west area of the Ecoregion, whereas ruffe lakes were more often found south of the Baltic Sea. 4. Controlling for the influence of nutrient concentration showed that lake morphology and geographical position were important determinants of fish assemblages. However, the variance explained was low (<20%), implying that biological interactions may also be important in forming the lake-specific fish assemblages. 5. The results suggest that fish assemblages differ between deep and shallow lakes, and between the north-west and south-east locations within the Central Plains Ecoregion. Accordingly, establishment of depth-related lake morphotypes is needed, and the European Ecoregions recommended to be used in evaluation systems according to the Water Framework Directive seem to be too coarse to reflect the subtle differences of fish species richness along geographical gradients.
