Size matters: experimental partitioning of the strength of fish herbivory on a fringing coral reef in Moorea,French Polynesia          下载免费PDF全文

Peggy Fong  Nicholas M. Frazier  Cameron Tompkins‐Cook  Ranjan Muthukrishnan  Caitlin R. Fong 《Marine Ecology》2016,37(5):933-942

While the importance of top‐down control by grazers in maintaining tropical reef community structure is well known, the effect of ‘fishing down the food web’, which simultaneously changes the abundance and size of herbivorous fishes, has received less attention. As many fishing practices target the biggest fish and regulations often set minimum size limits, understanding size‐dependency of this controlling force is important. We evaluated the hypothesis that reduction in the abundance and size of fish, regardless of species identity, reduces the role of herbivory in controlling algal abundance on reefs and assessed variation in efficacy of this top‐down control on different types of common macroalgae. We quantified herbivory rates within cages of differing opening sizes on assemblages of four common algal species (Padina boryana, Dictyota bartayresiana, Halimeda opuntia and Galaxaura fasciculata) on two fringing reefs in Moorea, French Polynesia. Small acanthurids (<15 cm length) were the dominant herbivorous fish while other herbivorous fish were rare. For the two most palatable algae, the majority of herbivory occurred in open plots, with herbivory reduced by >50% in the largest opening cages (6 × 6 cm) where the maximum size fish entering was 12 cm in length (mean = 7.6, SE = 0.4). Fish entering medium (4.5 × 4.5 cm openings, maximum fish length = 8 cm, mean = 6.3, SE = 0.4) and small (3 × 3 cm openings, no fish observed entering) cages had herbivory rates approximately equal to the control treatment (1 × 1 cm openings). Consumption varied among algal species, with minimal consumption of physically and chemically defended algae and no pattern across treatments. Our results demonstrate a need for management plans to not only maintain the overall abundance of herbivorous fish but to protect the largest sizes for effective top‐down control of algal communities.  相似文献   

Detecting and mapping slums using open data: a case study in Kenya     

Ron Mahabir  Peggy Agouris  Anthony Stefanidis  Arie Croitoru  Andrew T. Crooks 《International Journal of Digital Earth》2020,13(6):683-707

ABSTRACT

The worldwide slum population currently stands at over one billion, with substantial growth expected in the coming decades. Traditionally, slums have been mapped using information derived mainly from either physical indicators using remote sensing data, or socio-economic indicators using census data. Each data source on its own provides only a partial view of slums, an issue further compounded by data poverty in less-developed countries. To overcome such issues, this paper explores the fusion of traditional with emerging open data sources and data mining tools to identify additional indicators that can be used to detect and map the presence of slums, map their footprint, and map their evolution. Towards this goal, we develop an indicator database for slums using open sources of physical and socio-economic data that can be used to characterize slum settlements. Using this database, we then leverage data mining techniques to identify the most suitable combination of these indicators for mapping slums. Using three cities in Kenya as test cases, results show that the fusion of these data can improve the mapping accuracy of slums. These results suggest that the proposed approach can provide a viable solution to the emerging challenge of monitoring the growth of slums.  相似文献   

MNA as a Remedy for Arsenic Mobilized by Anthropogenic Inputs of Organic Carbon     

Janet G. Hering  Peggy A. O'Day  Robert G. Ford  Y. Thomas He  Azra Bilgin  H. James Reisinger  David R. Burris 《Ground Water Monitoring & Remediation》2009,29(3):84-92

The potential application of monitored natural attenuation (MNA) as a remedy for ground water contaminated with arsenic (As) is examined for a subset of contaminated sites, specifically those where naturally occurring As has been mobilized due to localized anthropogenic organic carbon (OC) releases. This includes sites subject to petroleum releases, exposure to landfill leachates, and OC additions for biostimulation of reductive dechlorination of chlorinated solvents. The key characteristic of these sites is that, under conditions prevailing before the anthropogenic OC introduction, the naturally occurring As in the subsurface was not mobile and did not adversely affect ground water quality. This suggests that, in the far-field (where background conditions are (re) established), As may be sequestered upon contact of the contaminated ground water with either or both the (uncontaminated) ambient ground water and the background aquifer minerals. The observed extents of elevated concentrations (or "footprints") of As and other chemical species, such as dissolved OC and iron (Fe), and related parameters, such as redox potential ( E _h) and dissolved oxygen, and their evolution over time can be used to assess the mobilization and sequestration of As and the potential feasibility of MNA as a remedial option. Ultimately, the capacity for As sequestration must be assessed in the context of the OC loading to the site, which may require "active" measures for source control. Monitoring is needed to confirm the continuing effectiveness of the MNA remedy or to indicate if contingency measures must be implemented.  相似文献   

Biogeochemical and ecological functioning of the low-salinity water lenses in the region of the Rhone River freshwater influence,NW Mediterranean Sea     

Frédéric Diaz  Jean-Jacques Naudin  Claude Courties  Peggy Rimmelin  Louise Oriol 《Continental Shelf Research》2008

A quasi-synoptic survey of a eulerian small grid was carried out twice during mid-spring 2002 in the Gulf of Lions, NW Mediterranean Sea. Analysis of hydrological core parameters reveal for the first time, in the region of freshwater influence (ROFI) of the Rhone River, the presence of low-salinity water (LSW) lenses. The present work details the biogeochemical and ecological functioning of the two LSW lenses from a combined analysis of nutrients and organic matter content, taxonomic assemblages of phytoplankton, primary productivity measurements and nitrogen regeneration fluxes. During the first survey, the lens observed is only detached in part from the Rhone River plume and is considered as a juvenile lens. In contrast, the second lens is totally detached from the plume forming a confined 3D structure with a large vertical development and is considered as having a more advanced maturity. A second survey, 4 days later, provided the opportunity to propose a complete sequence of ecological functioning of the LSW lenses, from their formation to a late stage of maturity just before dispersion. Nitrate contents and dissolved organic matter remain in high concentrations during the juvenile stages while the little available phosphate is rapidly exhausted. In such, an unbalanced-nutrient environment picoplankton appear to out-compete bacterioplankton for phosphate and other resources such as ammonium. In turn, the dominance of such prokaryotic assemblages could have involved the rapid development of microzooplankton. The sudden increase in phosphate observed in a more advanced stage of lens maturity is attributed to intense P-regeneration driven by the large abundance of microzooplankton. This top-down control does not seem to enable the prokaryotic assemblages to bloom again but the high concentrations of phosphate and nitrate favour the development of larger phytoplankton. These autotrophic communities rapidly exhaust nutrients and then decline in the confined ecosystem of the LSW lens that subsequently evolves towards oligotrophic conditions. In the observed last stage, small-sized phytoplankton again dominates the microbial assemblages and the trophic regime is mainly based on regenerated production. The long lifetime of the LSW lens compared to that of the Rhone River plume enables a deep transformation of the initial characteristics of the Rhone River freshwaters both in terms of nutrients balance and microbial food webs, especially through trophic cascading effects. Hence, we show that the LSW lenses have the potential to transfer nutrients and organic matter offshore but the nature (inorganic vs. organic) of the dominant compound exported will depend on the maturity of the lens at the time of its dispersion.  相似文献   

Assessing the impact of demographic characteristics on spatial error in volunteered geographic information features   总被引：3，自引：0，他引：3  

William F. Mullen  Steven P. Jackson  Arie Croitoru  Andrew Crooks  Anthony Stefanidis  Peggy Agouris 《GeoJournal》2015,80(4):587-605

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Decoupling of nutrient and grazer impacts on a benthic estuarine diatom assemblage     

Anna R. Armitage  Vanessa L. Gonzalez  Peggy Fong   《Estuarine, Coastal and Shelf Science》2009,84(3):375-380

Strong interactions between top-down (consumptive) and bottom-up (resource supply) trophic factors occur in many aquatic communities, but these forces can act independently in some microphytobenthic communities. Within benthic estuarine diatom assemblages, the dynamics of these interactions and how they vary with abiotic environmental conditions are not well understood. We conducted a field experiment at two sites with varying habitat characteristics to investigate the interactive effects of grazers and nutrients on benthic estuarine diatoms. We crossed snail (Cerithidea californica) and nutrient (nitrogen and phosphorus) addition treatments in enclosures on a restored tidal sandflat and a reference tidal mudflat in Mugu Lagoon, southern California. We repeated the study in summer 2000 and spring 2001 to assess temporal variation in the interactions. Snails caused a large decrease in diatom relative abundance and biomass (estimated as surface area); nutrients increased diatom abundance but did not alter diatom biomass. Snails and nutrients both reduced average diatom length, although the nutrient effect was weaker and temporally variable, occurring in the reference mudflat in the spring. There were few interactions between snail and nutrient addition treatments, suggesting that links between top-down and bottom-up forces on the diatom community were weak. There were no consistent differences in diatom assemblage characteristics between the two study sites, despite marked differences in sediment grain size and other abiotic characteristics between the sites. The strong diatom response to herbivores and weaker responses to enrichment differed from the previous studies where cyanobacteria increased in response to nutrient enrichment, further dissolving the “black box” perception of microphytobenthic communities.  相似文献   

A spatio-temporal model of housing prices based on individual sales transactions over time     

Tony E. Smith  Peggy Wu 《Journal of Geographical Systems》2009,11(4):333-355

A spatio-temporal model of housing price trends is developed that focuses on individual housing sales over time. The model allows for both the spatio-temporal lag effects of previous sales in the vicinity of each housing sale, and for general autocorrelation effects over time. A key feature of this model is the recognition of the unequal spacing between individual housing sales over time. Hence the residuals are modeled as a first-order autoregressive process with unequally spaced events. The maximum-likelihood estimation of this model is developed in detail, and tested in terms of simulations based on selected data. In addition, the model is applied to a small data set in the Philadelphia area.  相似文献   

The impact of poverty on fertility in Peninsular Malaysia: A cohort analysis     

Teo P 《GeoJournal》1991,23(2):125-133

The New Economic Policy (NEP) formulated in 1970 in Peninsular Malaysia had a two-fold aim of reducing poverty and redressing ethnic inequalities in wealth. The spatial bias of development on the west coast where the Chinese concentrate in the urban centres was also addressed. Population planning worked in tandem with NEP to reduce Malay to non-Malay differences in fertility. 1980 census data was evaluated to assess the impact of NEP on fertility transition in the country. Socioeconomic data for specific cohorts (15–24; 25–34 and 35–49) were collected and factor analysed to examine poverty conditions. The study found poverty to be differentiated by ethnicity. Malay poverty is high in both absolute (e.g. employment rate and education) and relative terms (as compared to the Chinese). The Chinese dimension is the exact opposite. Unfortunately, regional polarisation of wealth remains unchanged, even a decade after NEP. Poverty was regressed against cohort fertility and found to increase with it, especially for the older cohorts. Although NEP reduced fertility among the youngest cohort, its impact was not exceptionally large. The NEP is currently up for review. The apparent failure of the policy to achieve income equity and fertility transition must therefore be taken seriously.  相似文献   

Experimental abiotic synthesis of methanol in seafloor hydrothermal systems during diking events     

Kenneth M. Voglesonger  John R. Holloway  Eileen E. Dunn  Peter J. Dalla-Betta  Peggy A. O''Day 《Chemical Geology》2001,180(1-4):129-139

The abiotic synthesis of organic compounds in seafloor hydrothermal systems is one mechanism through which the subsurface environment could be supplied with reduced carbon. A flow-through, fixed-bed laboratory reactor vessel, the Catalytic Reactor Vessel (CRV) system, has been developed to investigate mineral–surface promoted organic synthesis at temperatures up to 400°C and pressures up to 30 MPa, conditions relevant to seafloor hydrothermal systems. Here we present evidence that metastable methanol can be directly synthesized from a gas-rich CO₂–H₂–H₂O mixture in the presence of a mineral substrate. Experiments have been performed without a substrate, with quartz, and with a mixture of quartz and magnetite. Temperatures and pressures in the experiments ranged from 200°C to 350°C and from 15 to 18 MPa, respectively. Maximum conversion of 5.8×10⁻⁴% CO₂ to CH₃OH per hour was measured using a mixture of magnetite and quartz in the reactor. After passivation of the stainless steel reactor vessel, experiments demonstrate that methanol is formed at temperatures up to 350°C in the presence of magnetite, and that the formation rate decreases over time. The experiments also show a loss of surface reactivity at 310°C and a regeneration of surface reactivity with increased temperature up to 350°C. Concentrations of CO₂ and H₂ used in the experiments simulate periodic, localized and dynamic conditions occurring within the seafloor during and immediately following magmatic diking events. High concentrations of CO₂ and H₂ may be generated by dike injection accompanied by exsolution of CO₂ and reaction of dissolved H₂O with FeO in the magma to form H₂. The experiments described here examine how the ephemeral formation of an H₂–CO₂-rich vapor phase within seafloor hydrothermal systems may supply reactants for abiotic organic synthesis reactions. These experiments show that the presence of specific minerals can promote the abiotic synthesis of simple organic molecules from common inorganic reactants such H₂O, CO₂ and H₂ under geologically realistic conditions.  相似文献   

Critical Issues in a Critical Era: Tourism in Southeast Asia     

Peggy Teo  & T.C. Chang 《Singapore journal of tropical geography》1998,19(2):119-129

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