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33.
The threatened forest habitats of the tropical Andes are reportedly being modified and destroyed 30% faster than their lowland
tropical counterparts, but impacts on the hyper-diverse resident avifauna have received little systematic study. We present
a baseline analysis of the effects of habitat modification on birds in a lower montane forest landscape in Ecuador, comparing
avian community composition in landscape elements subjected to different levels of human modification: primary forest, secondary
forest, edge habitat and agricultural land. We use data from a point count survey of 300 counts at 150 sites to test whether
community composition and density of birds with different reported habitat preferences and foraging strategies change among
landscape elements. Species richness and diversity were lowest in agricultural land, but on some measures, equally low in
primary forest. Richness and diversity peaked in secondary forest and edge habitat, but ordination and density analysis revealed
clear differences in their species composition. While secondary forest contained mostly forest-preferring species, edge habitat
harboured a mix of forest and open-land birds. There was a clearly structured gradient in species composition across landscape
elements, with densities of habitat specialists, foraging guilds and families varying considerably from primary forest to
agricultural land. Agricultural land was characterised by an assemblage of widespread, abundant species very different from
that in core forest habitats. As such, while the majority of montane forest birds appear resilient to a certain level of habitat
modification, they cannot persist, and are displaced, where forest has been cleared outright. We argue that, for Andean montane
forests, preservation of mature secondary forest offers flexibility in supplementing preserved primary forest areas to provide
sufficient habitat for the persistence of this incredibly diverse but severely threatened bird community. 相似文献
34.
35.
Susan E. Ward Richard D. Bardgett Niall P. McNamara John K. Adamson Nick J. Ostle 《Ecosystems》2007,10(7):1069-1083
Abstract
Using a 50-year-old field experiment, we investigated the effects of the long-term land management practices of repeated burning
and grazing on peatland vegetation and carbon dynamics (C). Plant community composition, C stocks in soils and vegetation,
and C fluxes of CO2, CH4 and DOC, were measured over an 18-month period. We found that both burning and grazing reduced aboveground C stocks, and
that burning reduced C stocks in the surface peat. Both burning and grazing strongly affected vegetation community composition,
causing an increase in graminoids and a decrease in ericoid subshrubs and bryophytes relative to unburned and ungrazed controls;
this effect was especially pronounced in burned treatments. Soil microbial properties were unaffected by grazing and showed
minor responses to burning, in that the C:N ratio of the microbial biomass increased in burned relative to unburned treatments.
Increases in the gross ecosystem CO2 fluxes of respiration and photosynthesis were observed in burned and grazed treatments relative to controls. Here, the greatest
effects were seen in the burning treatment, where the mean increase in gross fluxes over the experimental period was greater
than 40%. Increases in gross CO2 fluxes were greatest during the summer months, suggesting an interactive effect of land use and climate on ecosystem C cycling.
Collectively, our results indicate that long-term management of peatland has marked effects on ecosystem C dynamics and CO2 flux, which are primarily related to changes in vegetation community structure. 相似文献
36.
David M. Shuker Niall Currie Tara Hoole Emily R. Burdfield-Steel 《Population Ecology》2015,57(2):321-331
Reproductive interference arises when individuals of one species engage in reproductive activities with individuals of another, leading to fitness costs in one or both species. Reproductive interference (RI) therefore has two components. First, there must be mis-directed mating interactions. Second, there must be costs associated with these mis-directed interactions. Here we consider RI between four species of true bug in the family Lygaeidae, focusing in particular on the fitness consequences to Lygaeus equestris. The species we consider vary in their relationships with each other, including species in the same or different genus, and with or without natural overlap in their geographic ranges. First we show that inter-specific mating interactions, although not a certain outcome, are common enough to perhaps influence mating behaviour in these species (arising in up to 10 % of inter-specific pairings). Second, we show that reproductive interference can seriously reduce female fitness in L. equestris. Importantly, different species impose different costs of RI on L. equestris, with interactions with male Spilostethus pandurus inflicting fitness costs of similar magnitude to the costs of mating with con-specifics. On the other hand, mating interactions with male Oncopeltus fasciatus appear to have no effect on female fitness. In a follow-up experiment, when we allowed competition amongst just females of S. pandurus and L. equestris, the fitness of the latter was not reduced, arguing more strongly for the role of reproductive interference. However, in our final experiments under mass mating conditions with extended ecological interactions (including scope for competition for resources and cannibalism), the costs of RI were less apparent. Our data therefore suggest that the costs of RI will be context-specific and may act in concert with, or be swamped by, other ecological effects. We suggest that comparative studies of this sort that both mimic naturally occurring reproductive interference events, and also artificially generate new ones, will be necessary if we are to better understand the ecological and evolutionary significance of reproductive interference. 相似文献
37.
Investigation of Design Space for Freeze-Drying: Use of Modeling for Primary Drying Segment of a Freeze-Drying Cycle 总被引:1,自引:0,他引:1
Koganti VR Shalaev EY Berry MR Osterberg T Youssef M Hiebert DN Kanka FA Nolan M Barrett R Scalzo G Fitzpatrick G Fitzgibbon N Luthra S Zhang L 《AAPS PharmSciTech》2011,12(3):854-861
In this work, we explore the idea of using mathematical models to build design space for the primary drying portion of freeze-drying process. We start by defining design space for freeze-drying, followed by defining critical quality attributes and critical process parameters. Then using mathematical model, we build an insilico design space. Input parameters to the model (heat transfer coefficient and mass transfer resistance) were obtained from separate experimental runs. Two lyophilization runs are conducted to verify the model predictions. This confirmation of the model predictions with experimental results added to the confidence in the insilico design space. This simple step-by-step approach allowed us to minimize the number of experimental runs (preliminary runs to calculate heat transfer coefficient and mass transfer resistance plus two additional experimental runs to verify model predictions) required to define the design space. The established design space can then be used to understand the influence of critical process parameters on the critical quality attributes for all future cycles. 相似文献
38.
Raghwani J Rambaut A Holmes EC Hang VT Hien TT Farrar J Wills B Lennon NJ Birren BW Henn MR Simmons CP 《PLoS pathogens》2011,7(6):e1002064
Dengue is one of the most important infectious diseases of humans and has spread throughout much of the tropical and subtropical world. Despite this widespread dispersal, the determinants of dengue transmission in endemic populations are not well understood, although essential for virus control. To address this issue we performed a phylogeographic analysis of 751 complete genome sequences of dengue 1 virus (DENV-1) sampled from both rural (Dong Thap) and urban (Ho Chi Minh City) populations in southern Viet Nam during the period 2003-2008. We show that DENV-1 in Viet Nam exhibits strong spatial clustering, with likely importation from Cambodia on multiple occasions. Notably, multiple lineages of DENV-1 co-circulated in Ho Chi Minh City. That these lineages emerged at approximately the same time and dispersed over similar spatial regions suggests that they are of broadly equivalent fitness. We also observed an important relationship between the density of the human host population and the dispersion rate of dengue, such that DENV-1 tends to move from urban to rural populations, and that densely populated regions within Ho Chi Minh City act as major transmission foci. Despite these fluid dynamics, the dispersion rates of DENV-1 are relatively low, particularly in Ho Chi Minh City where the virus moves less than an average of 20 km/year. These low rates suggest a major role for mosquito-mediated dispersal, such that DENV-1 does not need to move great distances to infect a new host when there are abundant susceptibles, and imply that control measures should be directed toward the most densely populated urban environments. 相似文献
39.
This paper investigates the thermodynamics of gas-phase CO2 cascade uptake-reactions in the form of carbonate or monomethylcarbonate anions in the host cavity of various dinuclear octa-azacryptates
of m-CH2C6H4CH2 and 2,5-furano-spaced hosts, L
1 and L
2 cryptands, using density functional theory (DFT). The cascade process involves two stages, namely the formation of dinuclear
cryptate complexes, and the subsequent formation of either μ-carbonato cryptate complexes or μ-monomethylcarbonato cryptates.
The geometric and electronic structures were also investigated to determine the parameters that affect the stability of the
complexes. Natural bond orbital (NBO) analysis was used to investigate the interactions between the trapped anion and its
host. Ion selectivity was studied in terms of the formation of dinuclear cryptate complexes, while the basicity and nucleophilicity
of cryptands towards Lewis acids was also studied, and good agreement was found vis-à-vis available experimental data. 相似文献
40.
Greek R Shanks N 《Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences》2011,42(4):542-544
In this paper, we respond to arguments made concerning our position regarding animal models (Shelley, 2010) by briefly examining the fact that animals (human and nonhuman) are complex systems that have different evolutionary trajectories. This historical fact has implications for using animals as predictive models for human response to drugs and disease. 相似文献