bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxygen effects on methane production and oxidation in humid tropical forest soils
Authors: Teh Yit Arn , Silver Whendee L. , Conrad Mark E. 
Published: July 2005

AbstractWe investigated the effects of oxygen (O2) concentration on methane (CH4) production and oxidation in two humid tropical forests that differ in long‐term, time‐averaged soil O2 concentrations. We identified sources and sinks of CH4 through the analysis of soil gas concentrations, surface emissions, and carbon isotope measurements. Isotope mass balance models were used to calculate the fraction of CH4 oxidized in situ. Complementary laboratory experiments were conducted to determine the effects of O2 concentration on gross and net rates of methanogenesis. Field and laboratory experiments indicated that high levels of CH4 production occurred in soils that contained between 9±1.1% and 19±0.2% O2. For example, we observed CH4 concentrations in excess of 3% in soils with 9±1.1% O2. CH4 emissions from the lower O2 sites were high (22–101 nmol CH4 m−2 s−1), and were equal in magnitude to CH4 emissions from natural wetlands. During peak periods of CH4 efflux, carbon dioxide (CO2) emissions became enriched in 13C because of high methanogenic activity. Gross CH4 production was probably greater than flux measurements indicated, as isotope mass balance calculations suggested that 48–78% of the CH4 produced was oxidized prior to atmospheric egress. O2 availability influenced CH4 oxidation more strongly than methanogenesis. Gross CH4 production was relatively insensitive to O2 concentrations in laboratory experiments. In contrast, methanotrophic bacteria oxidized a greater fraction of total CH4 production with increasing O2 concentration, shifting the δ13C composition of CH4 to values that were more positive. Isotopic measurements suggested that CO2 was an important source of carbon for methanogenesis in humid forests. The δ13C value of methanogenesis was between −84‰ and −98‰, which is well within the range of CH4 produced from CO2 reduction, and considerably more depleted in 13C than CH4 formed from acetate.
The effect of elevated atmospheric CO2 and drought on sources and sinks of isoprene in a temperate and tropical rainforest mesocosm
Authors: Pegoraro Emiliano , Abrell Leif , Van Haren Joost , Barron‐Gafford Greg , Grieve Katherine Ann , Malhi Yadvinder , Murthy Ramesh , Lin Guanghui 
Published: July 2005

AbstractIsoprene is the most abundant volatile hydrocarbon emitted by many tree species and has a major impact on tropospheric chemistry, leading to formation of pollutants and enhancing the lifetime of methane, a powerful greenhouse gas. Reliable estimates of global isoprene emission from different ecosystems demand a clear understanding of the processes of both production and consumption. Although the biochemistry of isoprene production has been studied extensively and environmental controls over its emission are relatively well known, the study of isoprene consumption in soil has been largely neglected.Here, we present results on the production and consumption of isoprene studied by measuring the following different components: (1) leaf and soil and (2) at the whole ecosystem level in two distinct enclosed ultraviolet light‐depleted mesocosms at the Biosphere 2 facility: a cottonwood plantation with trees grown at ambient and elevated atmospheric CO2 concentrations and a tropical rainforest, under well watered and drought conditions. Consumption of isoprene by soil was observed in both systems. The isoprene sink capacity of litter‐free soil of the agriforest stands showed no significant response to different CO2 treatments, while isoprene production was strongly depressed by elevated atmospheric CO2 concentrations. In both mesocosms, drought suppressed the sink capacity, but the full sink capacity of dry soil was recovered within a few hours upon rewetting. We conclude that soil uptake of atmospheric isoprene is likely to be modest but significant and needs to be taken into account for a comprehensive estimate of the global isoprene budget. More studies investigating the capacity of soils to uptake isoprene in natural conditions are clearly needed.
Drought‐induced nitrous oxide flux dynamics in an enclosed tropical forest
Authors: Van Haren Joost L. M. , Handley Linda L. , Biel Karl Y. , Kudeyarov Valery N. , McLain Jean E. T. , Martens Dean A. , Colodner Debra C. 
Published: July 2005

AbstractEl Niño–La Niña cycles strongly influence dry and wet seasons in the tropics and consequently nitrous oxide (N2O) emissions from tropical rainforest soils. We monitored whole‐system and soil chamber N2O fluxes during 5‐month‐long droughts in the Biosphere 2 tropical forest to determine how rainfall changes N2O production. A consistent pattern of N2O flux changes during drought and subsequent wetting emerged from our experiments. Soil surface drying during the first days of drought, presumably increased gas transport out of the soil, which increased N2O fluxes. Subsequent drying caused an exponential decrease in whole‐system (4.0±0.1% day−1) and soil chamber N2O flux (8.9±0.8% day−1; south chamber; and 13.7±1.1% day−1; north chamber), which was highly correlated with soil moisture content. Soil air N2O concentration ([N2O]) and flux measurements revealed that surface N2O production persisted during drought. The first rainfall after drought triggered a N2O pulse, which amounted to 25% of drought‐associated reduction in N2O flux and 1.3±0.4% of annual N2O emissions. Physical displacement of soil air by water and soil chemistry changes during drought could not account for the observed N2O pulse. We contend that osmotic stress on the microbial biomass must have supplied the N source for pulse N2O, which was produced at the litter–soil interface. After the pulse, N2O fluxes were consistently 90% of predrought values. Nitrate change rate, nutrient, [N2O], and flux analyses suggested that nitrifiers dominated N2O production during the pulse and denitrifiers during wet conditions. N2O flux measurements in Biosphere 2, especially during the N2O pulse, demonstrate that large‐scale integration methods, such as flux towers, are essential for improving ecosystem N2O flux estimates.
Effect of elevated atmospheric CO2 on oviposition behavior in Manduca sexta moths
Authors: Abrell Leif , Guerenstein Pablo G. , Mechaber Wendy L. , Stange Gert , Christensen Thomas A. , Nakanishi Koji , Hildebrand John G. 
Published: July 2005

AbstractMoths can detect changes in environmental carbon dioxide (CO2) with extremely high sensitivity, but the role of CO2 in the biology of these and other insects is not well understood. Although CO2 has been demonstrated to influence egg‐laying (oviposition) behavior of the pyralid moth Cactoblastis cactorum and nectar foraging of the sphingid moth Manduca sexta, information about the generalized role of CO2 in the behavioral biology of these species is lacking. Comparative data are necessary to properly assess how the behaviors of different species may be modified by steadily rising levels of greenhouse gases in the environment. Experiments carried out in Biosphere 2 addressed whether changes in ambient CO2 levels play a role in the oviposition behaviors of M. sexta moths. In the first series of experiments, oviposition was measured inside a flight cage with different levels of nearly ambient or elevated CO2 (400, 800 or 1200 ppm). For each concentration, hostplants used as oviposition sites were grown from seed at a CO2 level that matched the environment inside the flight cage. Under homogenous levels of CO2, we observed no significant difference in oviposition behavior at the concentrations tested. In a second series of experiments, two groups of hostplants, each surrounded by a mini free‐air CO2 enrichment (FACE) ring, were assembled inside a flight cage. In this choice test, a dynamic plume of artificially high CO2 was generated around one group of test plants, while ambient CO2 was released around the second (control) group. After eggs were counted on both plant groups, M. sexta females showed a small preference for ovipositing on the control plants. Therefore, in contrast to C. cactorum females tested under similar dynamic flow conditions, M. sexta female oviposition was not strongly inhibited by elevated CO2. To investigate this phenomenon further, we used electrophysiological recording and found that the CO2 receptor cells in M. sexta, unlike those in C. cactorum, are not readily affected by elevated levels of ambient CO2. These findings therefore suggest that elevated background levels of CO2 affect the physiology of the CO2 detection system of M. sexta to a lesser extent than that of C. cactorum, and this correlates well with the observed differences in oviposition behavior between the two species under elevated levels of environmental CO2. Hostplants of C. cactorum are crassulacean acid metabolism plants that generate nocturnal CO2 sinks on the cladode surfaces, whereas, M. sexta hostplants are nocturnal sources of respiratory CO2. We hypothesize that the abrupt and continuing increase in global ambient CO2 levels will differentially alter the behavior and physiology of moths that use CO2 sinks and sources as sensory cues to find hostplants.
Selective harvest of sooty shearwater chicks: effects on population dynamics and sustainability
Authors: HUNTER CHRISTINE M. , CASWELL HAL 
Published: July 2005

Summary

Selectivity of harvest influences harvest sustainability because individuals with different characteristics contribute differently to population growth. We investigate the effects of selection based on chick weight on a traditional harvest of the sooty shearwater Puffinus griseus by Rakiura Maori in New Zealand.
We develop a periodic stage‐structured matrix population model and incorporate seasonal harvest of three weight classes of chicks. Intensity and selectivity of harvest are defined in terms of weight‐specific hazard functions.
We investigate the effect of harvest intensity and selectivity on population growth rate, λ, and the chick exploitation rate, E. We also consider the interaction of chick harvest and adult mortality.
λ decreases and E increases as harvest intensity increases. At low harvest intensities, selection has little effect on λ. At high harvest intensities, λ increases as selectivity increases because of the non‐linear relationship between harvest intensity and the probability of being harvested.
λ is determined almost completely by E, irrespective of the combination of harvest selectivity and intensity producing E. This is true for both general patterns of selectivity and specific patterns estimated from empirical data.
The elasticities of λ, the net reproductive rate and the generation time are unaffected by selectivity and show only small responses to harvest intensity.
Adult sooty shearwaters are killed as bycatch in long‐line and driftnet fisheries. Such mortality of adults has an effect on λ about 10‐fold greater than an equivalent level of chick harvest.
The sustainability of any combination of chick harvest and adult mortality depends on the resulting reduction in λ. We explore these results in relation to indices of sustainability, particularly the United States Marine Mammal Protection Act (MMPA) standards.
Predicting the growth of a small introduced muskox population using population prediction intervals
Authors: ASBJØRNSEN EINAR J. , SÆTHER BERNT‐ERIK , LINNELL JOHN D. C. , ENGEN STEINAR , ANDERSEN REIDAR , BRETTEN TORD 
Published: July 2005

Summary

A key issue in ecology is the prediction of future population fluctuations. Such population predictions are fundamental for population‐viability analysis and are essential for assessing the implications of various management actions. Development of reliable population predictions is however, difficult because it requires estimation and modelling of the separate effects of the deterministic components of the population dynamics as well as the stochastic influences on the population fluctuations. Here we model the stochastic dynamics of an introduced population of muskox Ovibos moschatus in the Dovrefjell mountains of central Norway, using a simple model without density regulation. Our aim is to examine quantitatively factors affecting the accuracy of the population projections by applying the concept of Population Prediction Interval (PPI).
The long‐term growth rate was % = 0·0511, assuming no density dependence. The environmental variance was relatively large (= 0·0159). This gives a deterministic growth rate of r = 0·0591. However, accounting for losses due to various kinds of human activities resulted in a nearly doubling of s (% = 0·0980).
Autumn temperature and late winter snow depth were each able to explain a significant proportion of the annual variation in population growth rates.
The impact of environmental stochasticity made the PPI wide after only a few years. Uncertainties in the estimates of the population parameters were quite small and had a minor impact on the PPI.
A sensitivity analysis showed that ignoring demographic stochasticity led to an overestimate of the environmental variance , but that the impact on the width of the PPI was small.
This study shows that reliable projections of future population growth, even based on simple population models without density regulation, are dependent on assessment of the accuracy in the population predictions that must be based on estimating and modelling the stochastic influences on the population dynamics.
Egg size variation does not affect offspring performance under intraspecific competition in Nasonia vitripennis, a gregarious parasitoid
Authors: LALONDE R. G. 
Published: July 2005

Summary

As with many insects, egg size variation is correlated with body size in the gregarious parasitoid, Nasonia vitripennis. I use this feature to test the hypothesis that egg size differences among parents affects the ability of their larvae to compete for limited resources within a superparasitized host.
I show that egg size asymmetries in parents that oviposit into the same host have no detectable effect on relative offspring performance, even under conditions of resource limitation.
Broods within a host that were initiated earlier attained greater average size than competing broods in the same host that were initiated later.
Individuals in the more numerous brood emerged consistently larger than individuals in the less numerous brood.
The possibility that siblings cooperate in competing for limited resources within a host and the potential role of sibling cooperation on egg size evolution is discussed.
Pairs of extreme avian personalities have highest reproductive success
Authors: BOTH CHRISTIAAN , DINGEMANSE NIELS J. , DRENT PIET J. , TINBERGEN JOOST M. 
Published: July 2005

Summary

Intraspecific variation in reproductive decisions is generally considered as a reaction to environmental circumstances. We show that variation in reproductive parameters also covaries with intraspecific variation in personality.
During 4 years, we studied reproductive parameters in a natural population of great tits in association with a personality trait: exploratory behaviour as measured in a novel environment.
Nest success, fledgling size and condition were all correlated with this personality trait. Slow‐exploring females had a higher nest success and largest fledglings. Fledgling condition was affected by the interaction between male and female exploratory behaviour, with assortative pairs at both ends of the behavioural spectrum producing fledglings in best condition. Fast‐exploring males bred in nestboxes that produced heavy fledglings in other years.
We hypothesize that fast‐exploring individuals are better able in defending or obtaining a high quality territory, while slow‐exploring individuals are either better parents or have better chicks which may, in part, explain the patterns in reproductive success. We discuss how these patterns in reproduction can explain earlier reported relationships between offspring recruitment and avian personality and may result in the maintenance of intraspecific genetic variation in personality.
Maternal yolk testosterone does not modulate parasite susceptibility or immune function in great tit nestlings
Authors: TSCHIRREN BARBARA , SALADIN VERENA , FITZE PATRICK S. , SCHWABL HUBERT , RICHNER HEINZ 
Published: July 2005

Summary

Maternal yolk hormones can enhance the development and phenotypic quality of nestling birds. Nevertheless, within species large differences in yolk androgen concentrations among clutches are observed. This differential allocation of maternal yolk hormones might be explained by a trade‐off between beneficial effects of yolk androgens and their associated costs.
Potential costs include an increased susceptibility to parasites in nestlings exposed to high concentrations of yolk androgens during embryonic development, weaker immune response or increased levels of circulating corticosterone that indirectly reduce immune function.
In a field study, we manipulated yolk testosterone in great tit (Parus major) eggs and tested the nestling's susceptibility to ectoparasites as measured by the parasites’ effect on growth, the cellular immune response, and the levels of circulating corticosterone.
At the end of the nestling period, nestlings originating from testosterone‐injected eggs were heavier than control nestlings. This effect was strongest in nestlings at the end of the size hierarchy, as shown by a significant interaction between hormone treatment and the nestlings’ size rank within nests.
High levels of yolk testosterone promoted growth of the nestling's body mass similarly in parasite‐infested and parasite‐free nests, and neither affected the levels of plasma corticosterone, nor the nestling's cell‐mediated immune response.
In summary, our results do not show negative short‐term effects of high concentrations of yolk testosterone on immune function or parasite susceptibility, but emphasize that maternal investment via deposition of yolk testosterone can promote fitness‐related growth and development of nestlings.
An experimental study on the causes of sex‐biased mortality in the black‐headed gull − the possible role of testosterone
Authors: MÜLLER WENDT , GROOTHUIS TON G. G. , EISING CORINE M. , DIJKSTRA COR 
Published: July 2005

Summary

During early development male offspring in avian species often suffer from enhanced mortality compared to female offspring. This has been attributed to different nutritional requirements, as sex‐biased mortality has been reported particularly in sexually size‐dimorphic species. However, other traits of the male phenotype, such as the embryonic hormone profile, have been suggested to contribute to this male disadvantage. In particular the negative effects of sex steroids on immune function may be causally involved.
We investigated the role of testosterone in the expression of male phenotype disadvantage through an experimental reduction of the availability of testosterone receptors by in‐ovo injection of an anti‐androgen (Flutamide©). Experimental nests contained a male and a female chick hatching from control treated eggs and a male and a female chick hatching from Flutamide treated eggs.
Male‐biased mortality occurred in control chicks at a stage where the sexes did not yet differ in their growth pattern, suggesting that sex‐specific nutritional requirements are not necessary for male‐biased mortality to occur. Control males and control females did not differ in their cell‐mediated immunity (CMI). This renders it unlikely that the observed skewed mortality was due to sex‐specific differences in the CMI.
Treatment of the eggs with flutamide antagonistically affected males and females. Flutamide treatment positively affected male development in particular through an enhanced growth rate, indicating that testosterone is involved in the expression of the male phenotype disadvantage. Female chicks hatching from Flutamide treated eggs were disadvantaged in growth and CMI. The possible pathways of this sex‐specific effect of Flutamide are discussed with regard to differential consequences of blocking the beneficial effects of maternal androgens and the interference with the process of sexual differentiation in males.
Space–time clustering of cowpox virus infection in wild rodent populations
Authors: CARSLAKE DAVID , BENNETT MALCOLM , BOWN KEVIN , HAZEL SARAH , TELFER SANDRA , BEGON MICHAEL 
Published: July 2005

SummaryThe spatial and temporal scale at which infectious animals pose a transmission risk to others may be inferred by a study of space–time interaction in the clustering of cases of infection.We analyse the distribution of bank voles and wood mice infectious with cowpox virus, using 7 years of monthly live‐trapping data from a woodland in north‐west England.A published method,K‐function analysis, is adapted to measure space–time interaction among infectious animals trapped on a grid system, where the populations at risk may vary in density.We hypothesized that the risk of cowpox transmission from an infectious animal would be contained within a temporal scale of one infectious period and a spatial scale of one home‐range diameter.Cowpox cases among wood mice showed significantly greater spatial clustering than the population at risk at the smallest spatial scale, corresponding to animals caught in the same location. At larger scales, and for bank voles at all scales, cowpox cases showed no spatial clustering beyond that expected from an association with host distribution.Cowpox cases among wood mice showed strong evidence of temporal clustering beyond that of the host population, indicating short‐lived outbreaks. No such effect was apparent among bank voles.Significant space–time interaction among cowpox cases was detected at the hypothesized spatial and temporal scales in both host species. This suggests that the risk of transmission is concentrated locally.Results are discussed in terms of transmission, including consideration of the appropriateness of distance and nearest‐neighbour based clustering tests to infections transmitted by local density and frequency dependent mechanisms.
Habitat‐specific normal and reverse diel vertical migration in the plankton‐feeding basking shark
Authors: SIMS DAVID W. , SOUTHALL EMILY J. , TARLING GERAINT A. , METCALFE JULIAN D. 
Published: July 2005

Summary

Megaplanktivores such as filter‐feeding sharks and baleen whales are at the apex of a short food chain (phytoplankton–zooplankton–vertebrate) and are sensitive indicators of sea‐surface plankton availability. Even though they spend the majority of their time below the surface it is still not known how most of these species utilize vertical habitat and adapt to short‐term changes in food availability.
A key factor likely to control vertical habitat selection by planktivorous sharks is the diel vertical migration (DVM) of zooplankton; however, no study has determined whether specific ocean‐habitat type influences their behavioural strategy. Based on the first high‐resolution dive data collected for a plankton‐feeding fish species we show that DVM patterns of the basking shark Cetorhinus maximus reflect habitat type and zooplankton behaviour.
In deep, well‐stratified waters sharks exhibited normal DVM (dusk ascent–dawn descent) by tracking migrating sound‐scattering layers characterized by Calanus and euphausiids. Sharks occupying shallow, inner‐shelf areas near thermal fronts conducted reverse DVM (dusk descent–dawn ascent) possibly due to zooplankton predator–prey interactions that resulted in reverse DVM of Calanus.
These opposite DVM patterns resulted in the probability of daytime‐surface sighting differing between these habitats by as much as two orders of magnitude. Ship‐borne surveys undertaken at the same time as trackings reflected these behavioural differences.
The tendency of basking sharks to feed or rest for long periods at the surface has made them vulnerable to harpoon fisheries. Ship‐borne and aerial surveys also use surface occurrence to assess distribution and abundance for conservation purposes. Our study indicates that without bias reduction for habitat‐specific DVM patterns, current surveys could under‐ or overestimate shark abundance by at least 10‐fold.