Browsing by Subject "Physical Geography"
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Item Open Access A baseline paleoecological study for the Santa Cruz Formation (late–early Miocene) at the Atlantic coast of Patagonia, Argentina(Palaeogeography, Palaeoclimatology, Palaeoecology, 2010-06) Vizcaíno, SF; Bargo, MS; Kay, RF; Fariña, RA; Di Giacomo, M; Perry, JMG; Prevosti, FJ; Toledo, N; Cassini, GH; Fernicola, JCCoastal exposures of the Santa Cruz Formation (late-early Miocene, southern Patagonia, Argentina) between the Coyle and Gallegos rivers have been a fertile ground for recovery of Miocene vertebrates for more than 100 years. The formation contains an exceptionally rich mammal fauna, which documents a vertebrate assemblage very different from any living community, even at the ordinal level. Intensive fieldwork performed since 2003 (nearly 1200 specimens have been collected, including marsupials, xenarthrans, notoungulates, litopterns astrapotheres, rodents, and primates) document this assertion. The goal of this study is to attempt to reconstruct the trophic structure of the Santacrucian mammalian community with precise stratigraphic control. Particularly, we evaluate the depauperate carnivoran paleoguild and identify new working hypotheses about this community. A database has been built from about 390 specimens from two localities: Campo Barranca (CB) and Puesto Estancia La Costa (PLC). All species have been classified as herbivore or carnivore, their body masses estimated, and the following parameters estimated: population density, on-crop biomass, metabolic rates, and the primary and secondary productivity. According to our results, this model predicts an imbalance in both CB and PLC faunas which can be seen by comparing the secondary productivity of the ecosystem and the energetic requirements of the carnivores in it. While in CB, the difference between carnivores and herbivores is six-fold, in PLC this difference is smaller, the secondary productivity is still around three times that of the carnivore to herbivore ratio seen today. If both localities are combined, the difference rises to around four-fold in favour of secondary productivity. Finally, several working hypotheses about the Santacrucian mammalian community and the main lineages of herbivores and carnivores are offered. © 2010 Elsevier B.V. All rights reserved.Item Open Access A formal Anthropocene is compatible with but distinct from its diachronous anthropogenic counterparts: a response to W.F. Ruddiman’s ‘three flaws in defining a formal Anthropocene’(Progress in Physical Geography, 2019-06-01) Zalasiewicz, J; Waters, CN; Head, MJ; Poirier, C; Summerhayes, CP; Leinfelder, R; Grinevald, J; Steffen, W; Syvitski, J; Haff, P; McNeill, JR; Wagreich, M; Fairchild, IJ; Richter, DD; Vidas, D; Williams, M; Barnosky, AD; Cearreta, A© The Author(s) 2019. We analyse the ‘three flaws’ to potentially defining a formal Anthropocene geological time unit as advanced by Ruddiman (2018). (1) We recognize a long record of pre-industrial human impacts, but note that these increased in relative magnitude slowly and were strongly time-transgressive by comparison with the extraordinarily rapid, novel and near-globally synchronous changes of post-industrial time. (2) The rules of stratigraphic nomenclature do not ‘reject’ pre-industrial anthropogenic signals – these have long been a key characteristic and distinguishing feature of the Holocene. (3) In contrast to the contention that classical chronostratigraphy is now widely ignored by scientists, it remains vital and widely used in unambiguously defining geological time units and is an indispensable part of the Earth sciences. A mounting body of evidence indicates that the Anthropocene, considered as a precisely defined geological time unit that begins in the mid-20th century, is sharply distinct from the Holocene.Item Open Access Convergent evolution in lemur environmental niches(Journal of Biogeography, 2020-04-01) Herrera, JPAim: To test the hypothesis that adaptive convergent evolution of climate niches occurred in multiple independent lemur lineages. Location: Madagascar. Taxon: Lemurs. Methods: I collected climate and altitude data from WorldClim and summarized the niches of almost all living lemurs (83 species) into phylogenetically controlled principal components. To test for convergent evolution, I searched for multiple, similar climate optima using multi-peak Ornstein–Uhlenbeck models (surface, l1-ou, bayou). I compared the observed level of climate convergence to that simulated under neutral and single-optimum models. To test if behavioural or morphological traits were related to climate niches, I used phylogenetic regressions with activity pattern, diet, and body size. Results: From an ancestral niche with high rainfall and low seasonality, four lemur lineages independently converged on climate niche optima characterized by high temperatures and low rainfall, supporting adaptive evolution in southwest deciduous and arid habitats. The observed level of convergence was more frequent than expected under Brownian motion and single-optimum simulations, which illustrates that the results are likely not a result of stochastic evolution over long time periods. Nocturnal and cathemeral activity patterns were common among lineages in the arid climate niche. Conclusion: Lemur climate niche evolution demonstrated that convergence explains the distribution of four independent clades in hot, arid environments of southwest Madagascar. The timing of these convergent shifts coincided with the origination of modern arid-adapted plant genera, some of which are important lemur food sources. These communities have high endemicity and are especially threatened by habitat loss. Arid environments are arenas in which convergent evolution is predicted to occur frequently.Item Open Access Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth(Earth Surface Dynamics, 2017-12-18) Brantley, SL; McDowell, WH; Dietrich, WE; White, TS; Kumar, P; Anderson, SP; Chorover, J; Ann Lohse, K; Bales, RC; Richter, DD; Grant, G; Gaillardet, JThe critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetative canopy through the soil and down to fresh bedrock and the bottom of the groundwater. All humans live in and depend on the CZ. This zone has three co-evolving surfaces: the top of the vegetative canopy, the ground surface, and a deep subsurface below which Earth's materials are unweathered. The network of nine CZ observatories supported by the US National Science Foundation has made advances in three broad areas of CZ research relating to the co-evolving surfaces. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response, in turn, impacts aboveground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences aboveground ecosystems. Third, several new mechanistic models now provide quantitative predictions of the spatial structure of the subsurface of the CZ.
Many countries fund critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gases, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each US observatory has succeeded in (i) synthesizing research across disciplines into convergent approaches; (ii) providing long-term measurements to compare across sites; (iii) testing and developing models; (iv) collecting and measuring baseline data for comparison to catastrophic events; (v) stimulating new process-based hypotheses; (vi) catalyzing development of new techniques and instrumentation; (vii) informing the public about the CZ; (viii) mentoring students and teaching about emerging multidisciplinary CZ science; and (ix) discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO enterprise in the United States and identify how such observatories could operate in the future as a network designed to generate critical scientific insights. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a driving question for future CZ science and ahubs-and-campaigns
model to address that question and target the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.Item Open Access Estimating the population size of lemurs based on their mutualistic food trees(Journal of Biogeography, 2018-11-01) Herrera, JP; Borgerson, C; Tongasoa, L; Andriamahazoarivosoa, P; Rasolofoniaina, BJR; Rakotondrafarasata, ER; Randrianasolo, JLRR; Johnson, SE; Wright, PC; Golden, CDAim: Species’ distributions and abundances are primarily determined by the suitability of environmental conditions, including climate and interactions with sympatric species, but also increasingly by human activities. Modelling tools can help in assessing the extinction risk of affected species. By combining species distribution modelling of abiotic and biotic niches with population size modelling, we estimated the abundance of 19 lemur taxa in three regions, especially focusing on 10 species that are considered Endangered or Critically Endangered. Location: Madagascar. Taxa: Lemurs (Primates) and angiosperm trees. Methods: We used climate data, field samples, and published occurrence data on trees to construct species distribution models (SDM) for lemur food tree species. We then inferred the SDMs for lemurs based on the probability of occurrence of their food trees as well as climate. Finally, we used tree SDMs, topography, distance to the forest edge, and field estimates of lemur population density to predict lemur abundance in general linear models. Results: The SDMs of lemur food trees were stronger predictors of the occurrence of lemurs than climate. The predicted probability of presence of food trees, slope, elevation, and distance from the forest edge were significant correlates of lemur density. We found that sixteen species had minimum estimated abundances greater than 10,000 individuals over >1,000km2. Three lemur species are especially threatened, with less than 2,500 individuals predicted for Cheirogaleus sibreei, and heavy hunting pressure for the relatively small populations of Indri indri and Hapalemur occidentalis. Main conclusions: Biotic interactors were important variables in SDMs for lemurs, allowing refined estimates of ranges and abundances. This paper provides an analytical workflow that can be applied to other taxonomic groups to substantiate estimates of species’ vulnerability to extinction.Item Open Access Habitat fragmentation and biodiversity conservation: key findings and future challenges(Landscape Ecology, 2016-02-01) Wilson, MC; Chen, XY; Corlett, RT; Didham, RK; Ding, P; Holt, RD; Holyoak, M; Hu, G; Hughes, AC; Jiang, L; Laurance, WF; Liu, J; Pimm, SL; Robinson, SK; Russo, SE; Si, X; Wilcove, DS; Wu, J; Yu, MItem Open Access Iron Age landscape changes in the Benoué River Valley, Cameroon(Quaternary Research (United States), 2019-09-01) Wright, DK; MacEachern, S; Ambrose, SH; Choi, J; Choi, JH; Lang, C; Wang, HCopyright © 2019 University of Washington. Published by Cambridge University Press. The introduction of agriculture is known to have profoundly affected the ecological complexion of landscapes. In this study, a rapid transition from C3 to C4 vegetation is inferred from a shift to higher stable carbon (13C/12C) isotope ratios of soils and sediments in the Benoué River Valley and upland Fali Mountains in northern Cameroon. Landscape change is viewed from the perspective of two settlement mounds and adjacent floodplains, as well as a rock terrace agricultural field dating from 1100 cal yr BP to the recent past (<400 cal yr BP). Nitrogen (15N/14N) isotope ratios and soil micromorphology demonstrate variable uses of land adjacent to the mound sites. These results indicate that Early Iron Age settlement practices involved exploitation of C3 plants on soils with low δ15N values, indicating wetter soils. Conversely, from the Late Iron Age (>700 cal yr BP) until recent times, high soil and sediment δ13C and δ15N values reflect more C4 biomass and anthropogenic organic matter in open, dry environments. The results suggest that Iron Age settlement practices profoundly changed landscapes in this part of West Africa through land clearance and/or utilization of C4 plants.Item Open Access Large trees drive forest aboveground biomass variation in moist lowland forests across the tropics(Global Ecology and Biogeography, 2013-12) Slik, JWF; Paoli, G; Mcguire, K; Amaral, I; Barroso, J; Bastian, M; Blanc, L; Bongers, F; Boundja, P; Clark, C; Collins, M; Dauby, G; Ding, Y; Doucet, J-L; Eler, E; Ferreira, L; Forshed, O; Fredriksson, G; Gillet, J-F; Harris, D; Leal, M; Laumonier, Y; Malhi, Y; Mansor, A; Martin, E; Miyamoto, K; Araujo-Murakami, A; Nagamasu, H; Nilus, R; Nurtjahya, E; Oliveira, A; Onrizal, O; Parada-Gutierrez, A; Permana, A; Poorter, L; Poulsen, J; Ramirez-Angulo, H; Reitsma, J; Rovero, F; Rozak, A; Sheil, D; Silva-Espejo, J; Silveira, M; Spironelo, W; ter Steege, H; Stevart, T; Navarro-Aguilar, GE; Sunderland, T; Suzuki, E; Tang, J; Theilade, I; van der Heijden, G; van Valkenburg, J; Van Do, T; Vilanova, E; Vos, V; Wich, S; Wöll, H; Yoneda, T; Zang, R; Zhang, M-G; Zweifel, NAim: Large trees (d.b.h.≥70cm) store large amounts of biomass. Several studies suggest that large trees may be vulnerable to changing climate, potentially leading to declining forest biomass storage. Here we determine the importance of large trees for tropical forest biomass storage and explore which intrinsic (species trait) and extrinsic (environment) variables are associated with the density of large trees and forest biomass at continental and pan-tropical scales. Location: Pan-tropical. Methods: Aboveground biomass (AGB) was calculated for 120 intact lowland moist forest locations. Linear regression was used to calculate variation in AGB explained by the density of large trees. Akaike information criterion weights (AICc-wi) were used to calculate averaged correlation coefficients for all possible multiple regression models between AGB/density of large trees and environmental and species trait variables correcting for spatial autocorrelation. Results: Density of large trees explained c. 70% of the variation in pan-tropical AGB and was also responsible for significantly lower AGB in Neotropical [287.8 (mean)±105.0 (SD) Mg ha-1] versus Palaeotropical forests (Africa 418.3±91.8 Mg ha-1; Asia 393.3±109.3 Mg ha-1). Pan-tropical variation in density of large trees and AGB was associated with soil coarseness (negative), soil fertility (positive), community wood density (positive) and dominance of wind dispersed species (positive), temperature in the coldest month (negative), temperature in the warmest month (negative) and rainfall in the wettest month (positive), but results were not always consistent among continents. Main conclusions: Density of large trees and AGB were significantly associated with climatic variables, indicating that climate change will affect tropical forest biomass storage. Species trait composition will interact with these future biomass changes as they are also affected by a warmer climate. Given the importance of large trees for variation in AGB across the tropics, and their sensitivity to climate change, we emphasize the need for in-depth analyses of the community dynamics of large trees. © 2013 John Wiley & Sons Ltd.Item 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.Item Open Access The effect of accelerated soil erosion on hillslope morphology(Earth Surface Processes and Landforms, 2019-12-01) Bonetti, S; Richter, DD; Porporato, A© 2019 John Wiley & Sons, Ltd. Intensive agricultural land use can have detrimental effects on landscape properties, greatly accelerating soil erosion, with consequent fertility loss and reduced agricultural potential. To quantify the effects of such erosional processes on hillslope morphology and gain insight into the underlying dynamics, we use a twofold approach. First, a statistical analysis of topographical features is conducted, with a focus on slope and gradient distributions. The accelerated soil erosion is shown to be fingerprinted in the distribution tails, which provide a clear statistical signature of this human-induced land modification. Theoretical solutions are then derived for the hillslope morphology and the associated creep and runoff erosion fluxes, allowing us to distinguish between the main erosional mechanisms operating in disturbed and undisturbed areas. We focus our application on the landscape at the Calhoun Critical Zone Observatory in the US Southern Piedmont, where severe soil erosion followed intensive cotton cultivation, resulting in highly eroded and gullied hillslopes. The observed differences in hillslope morphologies in disturbed and undisturbed areas are shown to be related to the disruption of the natural balance between soil creep and runoff erosion. The relaxation time required for the disturbed hillslopes to reach a quasi-equilibrium condition is also investigated. © 2019 John Wiley & Sons, Ltd.