Browsing by Subject "PATTERNS"

Now showing 1 - 7 of 7

Open Access
Emergent productivity regimes of river networks
(Limnology and Oceanography Letters, 2019-10) Koenig, LE; Helton, AM; Savoy, P; Bertuzzo, E; Heffernan, JB; Hall, RO; Bernhardt, ES
Open Access
Forest elephant movement and habitat use in a tropical forest-grassland mosaic in Gabon.
(PloS one, 2018-01) Mills, Emily C; Poulsen, John R; Fay, J Michael; Morkel, Peter; Clark, Connie J; Meier, Amelia; Beirne, Christopher; White, Lee JT
Poaching of forest elephants (Loxodonta cyclotis) for ivory has decimated their populations in Central Africa. Studying elephant movement can provide insight into habitat and resource use to reveal where, when, and why they move and guide conservation efforts. We fitted 17 forest elephants with global positioning system (GPS) collars in 2015 and 2016 in the tropical forest-grassland mosaic of the Wonga Wongué Presidential Reserve (WW), Gabon. Using the location data, we quantified movement distances, home ranges, and habitat use to examine the environmental drivers of elephant movements and predict where elephants occur spatially and temporally. Forest elephants, on average, traveled 2,840 km annually and had home ranges of 713 km2, with males covering significantly larger home ranges than females. Forest elephants demonstrated both daily and seasonal movement patterns. Daily, they moved between forest and grassland at dawn and dusk. Seasonally, they spent proportionally more time in grassland than forest during the short-wet season when grasses recruit. Forest elephants also traveled faster during the short-wet season when fruit availability was greatest, likely reflecting long, direct movements to preferred fruiting tree species. Forest elephants tended to select areas with high tree and shrub density that afford cover and browse. When villages occurred in their home ranges elephants spent a disproportionate amount of time near them, particularly in the dry season, probably for access to agricultural crops and preferred habitat. Given the importance of the grassland habitat for elephants, maintenance of the forest-grassland matrix is a conservation priority in WW. Law enforcement, outreach, and education should focus on areas of potential human-elephant conflict near villages along the borders of the reserve. GPS-tracking should be extended into multi-use areas in the peripheries of protected areas to evaluate the effects of human disturbance on elephant movements and to maintain connectivity among elephant populations in Gabon.
Open Access
Mammalian faunas, ecological indices, and machine-learning regression for the purpose of paleoenvironment reconstruction in the Miocene of South America
(Palaeogeography, Palaeoclimatology, Palaeoecology, 2019-03-15) Spradley, JP; Glazer, BJ; Kay, RF
© 2019 Elsevier B.V. Reconstructing paleoenvironments has long been considered a vital component for understanding community structure of extinct organisms, as well as patterns that guide evolutionary pathways of species and higher-level taxa. Given the relative geographic and phylogenetic isolation of the South American continent throughout much of the Cenozoic, the South American fossil record presents a unique perspective of mammalian community evolution in the context of changing climates and environments. Here we focus on one line of evidence for paleoenvironment reconstruction: ecological diversity, i.e. the number and types of ecological niches filled within a given fauna. We propose a novel approach by utilizing ecological indices as predictors in two regressive modeling techniques—Random Forest (RF) and Gaussian Process Regression (GPR)—which are applied to 85 extant Central and South American localities to produce paleoecological prediction models. Faunal richness is quantified via ratios of ecologies within the mammalian communities, i.e. ecological indices, which serve as predictor variables in our models. Six climate/habitat variables were then predicted using these ecological indices: mean annual temperature (MAT), mean annual precipitation (MAP), temperature seasonality, precipitation seasonality, canopy height, and net primary productivity (NPP). Predictive accuracy of RF and GPR is markedly higher when compared to previously published methods. MAT, MAP, and temperature seasonality have the lowest predictive error. We use these models to reconstruct paleoclimatic variables in two well-sampled Miocene faunas from South America: fossiliferous layers (FL) 1–7, Santa Cruz Formation (Early Miocene), Santa Cruz Province, Argentina; and the Monkey Beds unit, Villavieja Formation (Middle Miocene) Huila, Colombia. Results suggest general concordance with published estimations of precipitation and temperature, and add information with regards to the other climate/habitat variables included here. Ultimately, we believe that RF and GPR in conjunction with ecological indices have the potential to contribute to paleoenvironment reconstruction.
Open Access
Modifications of 2:1 clay minerals in a kaolinite-dominated Ultisol under changing land-use regimes
(Clays and Clay Minerals, 2018-02-01) Austin, JC; Perry, A; Richter, DD; Schroeder, PA
© 2018, Clay Minerals Society. All rights reserved. Chemical denudation and chemical weathering rates vary under climatic, bedrock, biotic, and topographic conditions. Constraints for landscape evolution models must consider changes in these factors on human and geologic time scales. Changes in nutrient dynamics, related to the storage and exchange of K+ in clay minerals as a response to land use change, can affect the rates of chemical weathering and denudation. Incorporation of these changes in landscape evolution models can add insight into how land use changes affect soil thickness and erodibility. In order to assess changes in soil clay mineralogy that result from land-use differences, the present study contrasts the clay mineral assemblages in three proximal sites that were managed differently over nearly the past two centuries where contemporary vegetation was dominated by old hardwood forest, old-field pine, and cultivated biomes. X-ray diffraction (XRD) of the oriented clay fraction using K-, Mg-, and Na-saturation treatments for the air-dried, ethylene glycol (Mg- EG and K-EG) solvated, and heated (100, 350, and 550ºC) states were used to characterize the clay mineral assemblages. XRD patterns of degraded biotite (oxidized Fe and expelled charge-compensating interlayer K) exhibited coherent scattering characteristics similar to illite. XRD patterns of the Mg-EG samples were, therefore, accurately modeled using NEWMOD2® software by the use of mineral structure files for discrete illite, vermiculite, kaolinite, mixed-layer kaolinite-smectite, illite-vermiculite, kaolinite-illite, and hydroxy-interlayered vermiculite. The soil and upper saprolite profiles that formed on a Neoproterozoic gneiss in the Calhoun Experimental Forest in South Carolina, USA, revealed a depth-dependence for the deeply weathered kaolinitic to the shallowly weathered illitic/vermiculitic mineral assemblages that varied in the cultivated, pine, and hardwood sites, respectively. An analysis of archived samples that were collected over a five-decade growth period from the pine site suggests that the content of illite-like layers increased at the surface within 8 y. Historical management of the sites has resulted in different states of dynamic equilibrium, whereby deep rooting at the hardwood and pine sites promotes nutrient uplift of K from the weathering of orthoclase and micas. Differences in the denudation rates at the cultivated, pine, and hardwood sites through time were reflected by changes in the soil clay mineralogy. Specifically, an increased abundance of illite-like layers in the surface soils can serve as a reservoir of K+.
Open Access
Origins of the endemic scaly tree ferns on the galápagos and Cocos Islands
(International Journal of Plant Sciences, 2015-11-01) Kao, T; Pryer, KM; Turner, MD; White, RA; Korall, P
© 2015 by The University of Chicago. All rights reserved. Premise of research. Successful long-distance dispersal is rarely observed in scaly tree ferns (Cyatheaceae). Nevertheless, recent molecular evidence has suggested that the four endemic scaly tree ferns on the Galápagos Archipelago (Cyathea weatherbyana) and Cocos Island (Cyathea alfonsiana, Cyathea nesiotica, and Cyathea notabilis), two oceanic island groups west of Central and northern South America, probably each originated from different mainland America ancestors. However, the phylogenetic relationships inferred among these endemics and their mainland relatives have been unclear. This study is aimed at better resolving the relationships and tracing the origins of these island endemics. Methodology. Five plastid regions from 35 Cyathea species were analyzed to reconstruct phylogenetic relationships using parsimony, likelihood, and Bayesian approaches. We also estimated divergence times of these species, and our chronogram was used to reconstruct their biogeographical range history. Pivotal results. Our well-resolved phylogenetic tree of Cyathea, which is in agreement with previous studies, shows that when the four Galápagos and Cocos endemics are included, they each belong to separate subclades. Our biogeographical study suggests that the four endemics originated from independent colonization events from mainland America and that there was no dispersal of Cyathea between the island groups. We reveal more detailed relationships among the endemics and their respective close mainland relatives; some of these relationships differ from previous studies. Our findings are corroborated by new morphological data from ongoing stem anatomy studies. Conclusions. The four scaly tree ferns endemic to the Galápagos and Cocos Islands each did indeed originate as independent colonization events from separate sources in mainland America, and their closest relatives are identified here.
Open Access
Protected areas and biodiversity conservation in India
(Biological Conservation, 2019-09-01) Ghosh-Harihar, Mousumi; An, Ruby; Athreya, Ramana; Borthakur, Udayan; Chanchani, Pranav; Chetry, Dilip; Datta, Aparajita; Harihar, Abishek; Karanth, Krithi K; Mariyam, Dincy; Mohan, Dhananjai; Onial, Malvika; Ramakrishnan, Uma; Robin, VV; Saxena, Ajai; Shahabuddin, Ghazala; Thatte, Prachi; Vijay, Varsha; Wacker, Kristen; Mathur, Vinod B; Pimm, Stuart L; Price, Trevor D
Three well-supported generalizations in conservation biology are that developing tropical countries will experience the greatest biodiversity declines in the near future, they are some of the least studied areas in the world, and in these regions especially, protection requires local community support. We assess these generalizations in an evaluation of protected areas in India. The 5% of India officially protected covers most ecoregions and protected areas have been an important reason why India has suffered no documented species extinctions in the past 70 years. India has strong legislation favouring conservation, government investment focused on 50 Tiger Reserves, and government compensation schemes that facilitate local support, all of which brighten future prospects. However, many protected areas are too small to maintain a full complement of species, making connectivity and species use of buffer zones a crucial issue. Conservation success and challenges vary across regions according to their development status. In less developed areas, notably the biodiverse northeast Himalaya, protected areas maintaining the highest biodiversity result from locally-focused efforts by dedicated individuals. Across India, we demonstrate considerable opportunities to increase local income through ecotourism. Our evaluation confirms a lack of data, increasing threats, and the importance of local support. Research on biodiversity in buffer zones, development of long-term monitoring schemes, and assessment of cash and conservation benefits from tourism are in particular need. For policy makers, two main goals should be the development of monitoring plans for ‘eco-sensitive zones’ around protected areas, and a strong emphasis on preserving established protected areas.
Open Access
The Historical Demography of Racial Segregation
(American Sociological Review, 2015) Grigoryeva, A; Ruef, M
Standard measures of residential segregation tend to equate spatial with social proximity. This assumption has been increasingly subject to critique among demographers and ethnographers and becomes especially problematic in historical settings. In the late nineteenth-century United States, standard measures suggest a counterintuitive pattern: southern cities, with their long history of racial inequality, had less residential segregation than urban areas considered to be more racially tolerant. By using census enumeration procedures, we develop a sequence measure that captures a more subtle “backyard” pattern of segregation, where white families dominated front streets and blacks were relegated to alleys. Our analysis of complete household data from the 1880 Census documents how segregation took various forms across the postbellum United States. Whereas northern cities developed segregation via racialized neighborhoods, substituting residential inequality for the status inequality of slavery, southern cities embraced street-front segregation that reproduced the racial inequality that existed under slavery.