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Results 701 - 750 of 1050
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Tomy Gregg T - - 2004
The extent of bioaccumulation of hexabromocyclododecane (HBCD) isomers (alpha, beta, and gamma) was determined in the Lake Ontario pelagic food web using liquid chromatography tandem mass spectrometry (LC/MS/MS). Concentrations of the alpha-isomer were consistently higher than that of the gamma-isomer. The beta-isomer was below method detection limits in all samples. ...
Rothe, Jan
Stable isotope techniques were used to identify regeneration patterns in the trophic structure of the reassembling communities in order to describe the development of a disturbed grassland ecosystem (Steudnitz) that had been subjected to anthropogenic pollution for more than 30 years. Mean values of the frequency distribution of [delta]<sup>15</sup>N differences ...
Nowak Martin A - - 2004
To explain the evolution of cooperation by natural selection has been a major goal of biologists since Darwin. Cooperators help others at a cost to themselves, while defectors receive the benefits of altruism without providing any help in return. The standard game dynamical formulation is the 'Prisoner's Dilemma', in which ...
Arii K - - 2004
Previous studies have shown that high-resolution, empirical food webs possess a non-random network structure, typically characterized by uniform or exponential degree distributions. However, the empirical food webs that have been investigated for their structural properties represent local communities that are only a subset of a larger pool of regionally coexisting ...
Weithoff Guntram - - 2004
Herbivore populations are commonly restricted by resource limitation, by predation or a combination of the two. Food supplement experiments are suitable for investigating the extent of food limitation at any given time. The main part of this study was performed in an extremely acidic lake (pH 2.7) where the food ...
Ruess Liliane - - 2004
This study analyses trophic interactions between soil fungi, micro- and mesofauna in microcosm experiments. The trophic shift of 15N and fatty acids (FAs) was investigated in different food chains, which comprised either two (fungi and grazers) or three (fungi, nematodes and Collembola) levels. Contrary to the widely accepted assumption of ...
Keller Gerta - - 2004
Since the early l990s the Chicxulub crater on Yucatan, Mexico, has been hailed as the smoking gun that proves the hypothesis that an asteroid killed the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K-T) boundary 65 million years ago. Here, we report evidence from ...
Patrick T. Gregory
Generalist species are often both widely distributed and abundant. They also are often plastic in their ecology, both spatially and temporally, in response to variation in resources. Here, we study the food habits of the widespread European Grass Snake, Natrix natrix, in Kent in southeastern England. As elsewhere in their ...
Brown David H - - 2004
Predators can have positive impacts on their prey through such mechanisms as nutrient mineralization and prey transport. These positive feedbacks have the potential to change predictions based on food web theory, such as the assertion that enrichment is destabilizing. We present a model of a simple food web, consisting of ...
Williams Richard J - - 2004
While trophic levels have found broad application throughout ecology, they are also in much contention on analytical and empirical grounds. Here, we use a new generation of data and theory to examine long-standing questions about trophic-level limits and degrees of omnivory. The data include food webs of the Chesapeake Bay, ...
Oro Daniel - - 2004
Few studies have addressed the effects of food availability as a proximate factor affecting local adult survival in long-lived organisms and their consequences at local population dynamics. We used capture-recapture analysis of resightings of 10 birth cohorts of ringed Audouin's gulls, Larus audouinii, to estimate adult survival and dispersal (both ...
Votier Stephen C - - 2004
It is clear that discards from commercial fisheries are a key food resource for many seabird species around the world. But predicting the response of seabird communities to changes in discard rates is problematic and requires historical data to elucidate the confounding effects of other, more 'natural' ecological processes. In ...
Aukema Brian H - - 2004
Multiple predator species feeding on a common prey can lead to higher or lower predation than would be expected by simply combining their individual effects. Such emergent multiple predator effects may be especially prevalent if predators share feeding habitat. Despite the prevalence of endophagous insects, no studies have examined how ...
Ballantyne Ford F - - 2004
A three-state, discrete-time Markov chain is used to model the dynamics of energy flow in a tri-trophic food web. The distribution of energy in the three trophic levels is related to the rates of flow between the trophic levels and calculated for the entire range of possible flow values. These ...
Whitaker David - - 2004
We demonstrate that the 1st- and 2nd-order characteristics of a visual stimulus can have a profound influence on each other in terms of perceived position. We use the parameter of spatial separation to selectively manipulate the effect of one characteristic upon the other. 1st-order features have their largest effect upon ...
Williams, Dudley
(1) The diets of juvenile and adult sympatric sticklebacks (A. quadracus, G. aculeatus, G. wheatlandi and P. pungitius) were compared with the abundance of potential prey in the environment. (2) The sites exhibited differences in salinity and temperature and these were related to the observed differences in stickleback population structure. ...
Békri Khalida - - 2004
This study investigated the potential in vivo immunotoxic effects of tributyltin (TBT) on amoebocytes of 6-armed seastar Leptasterias polaris. Tested animals were contaminated by trophic transfer via alive contaminated prey consisting of blue mussels (3microg TBT g(-1) wet weight (WW) tissue) exposed to seawater containing dissolved TBT. Four biomarkers of ...
Banasek-Richter Carolin - - 2004
Food-web descriptors serve as a means for among-web comparisons that are necessary for the discovery of regularities in respect to food-web structure. Qualitative descriptors were however found to be highly sensitive to varying levels of sampling effort. To circumvent these shortcomings, quantitative counterparts were proposed which take the magnitude of ...
Kooi B W - - 2004
Basic Lotka-Volterra type models in which mutualism (a type of symbiosis where the two populations benefit both) is taken into account, may give unbounded solutions. We exclude such behaviour using explicit mass balances and study the consequences of symbiosis for the long-term dynamic behaviour of a three species system, two ...
Feuchtmayr, Heidrun
Summary The aim of this work was the comparison of the impact of copepods and cladocerans, the major guilds within the mesozooplankton in marine and freshwater habitats, respectively, on lower trophic food levels. Differences between copepods and cladocerans were expected because these two zooplankton guilds differ in their feeding behavior; ...
Poirot, Ceisha Iana
Nest success, feeding behavior and anti-predator strategies, were studied to determine if bellbirds (Anthornis melanura) are limited by predation and if pest control can relieve the pressures of predation so that food supply may become a limiting factor for bellbirds. The nest success of bellbirds at the Rotoiti Nature Recovery ...
Poirot, Ceisha Iana
Nest success, feeding behavior and anti-predator strategies, were studied to determine if bellbirds (Anthornis melanura) are limited by predation and if pest control can relieve the pressures of predation so that food supply may become a limiting factor for bellbirds. The nest success of bellbirds at the Rotoiti Nature Recovery ...
Perez M H - - 2004
The waterways and associated salt marshes along the western border of Staten Island, New York (Arthur Kill) have long been under environmental duress. Environmental threats include industrial and municipal discharges, oil spills, and possible leachate from landfills. These impacts are compounded due to the low flushing of this body of ...
Ma Tao-Wu - - 2004
The potential endocrine disrupting effects and other toxicity effects on aquatic biota resulted from food uptake was simulated by feeding the laboratory cultured rare minnow( Gobiocypris rarus) with field collected Limnodrilus sp. The results indicated that the food chain processes affected significantly the growth, slightly reduced gonadosomatic indices, and elevated ...
Øien Alf H - - 2004
Attempts are presented of an analogue modelling of Daphnia responses to various influences and stimuli, as distribution of food and of predators. An aim of the study is to examine to what extent a statistical-mechanical approach may be useful as a tool in modelling of Daphnia swarms behaviour. In the ...
Badii Mohammad H - - 2004
The aims of this study were: (a) determine the prey stage preference of female Euseius hibisci (Chant) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), (b) assess the functional response of the predator females to the varying densities of eggs, larvae, or protonymphs of T. urticae, ...
Dahlhoff Elizabeth P - - 2004
Studies investigating the effects of temperature, food availability, or other physical factors on the physiology of marine animals have led to the development of biochemical indicators of growth rate, metabolic condition, and physiological stress. Measurements of metabolic enzyme activity and RNA/DNA have been especially valuable as indicators of condition in ...
Jackson Kate - - 2004
In this study we investigated how ophiophagous snakes are able to ingest prey snakes that equal or exceed their own length. We used X-ray video, standard video, dissection, and still X-rays to document the process of ophiophagy in kingsnakes (Lampropeltis getula) feeding on corn snakes (Elaphe guttata). Most kingsnakes readily ...
Kroon Annemarie - - 2004
Whenever diapause induction triggers movement into another microhabitat or the development of protective morphological structures, this may also alter predation risk. If the risk of being eaten is lower in the diapause phase, then there may be selection favouring diapause induction in response to predators or their cues. In this ...
Quinn Margaret R - - 2003
This study examines detrimental effects of acid mine drainage (AMD) on stream invertebrate communities and tests for a direct relationship between trophic position and accumulation of three metals (Fe, Cu, Zn) by stream invertebrates in situ. On two dates in each of seven stream sites, we measured food chain length, ...
HilleRisLambers Reinier - - 2003
Competition and predation are fundamental interactions structuring food webs. However, rather than always following these neat theoretical categories, mixed interactions are ubiquitous in nature. Of particular importance are omnivorous species, such as intra-guild predators that can both compete with and predate on their prey. Here, we examine trade-offs between competitive ...
LaFiandra Emily May - - 2004
Predator-induced defenses can result from non-contact cues associated with the presence of a feeding predator; however, the nature of the predator cue has not been determined. We tested the role of two non-contact cues, metabolites of digestion of conspecific prey released by the predator and alarm pheromones released by attacked ...
Imre I - - 2004
Optimal territory size models predict a decrease in territory size with increasing food abundance. However, most of these models may not be applicable to juvenile salmonids in streams, because they defend contiguous territories at high densities. The optimal size of a contiguous territory is predicted to (1) be independent of ...
Krause Ann E - - 2003
Compartments in food webs are subgroups of taxa in which many strong interactions occur within the subgroups and few weak interactions occur between the subgroups. Theoretically, compartments increase the stability in networks, such as food webs. Compartments have been difficult to detect in empirical food webs because of incompatible approaches ...
Kear Benjamin P - - 2003
Despite ichthyosaurs being one of the most extensively studied Mesozoic marine reptile groups, there is little documented direct evidence of dietary habits in most taxa. Here, we report the discovery of hatchling-sized marine protostegid turtle remains and an enantiornithine bird (in association with actinopterygian fish and phosphatic nodules) within the ...
Brucet Balmaña, Sandra
Zooplankton community structure (composition, diversity, dynamics and trophic relationships) of Mediterranian marshes, has been analysed by means of a size based approach. In temporary basins the shape of the biomass-size spectra is related to the hydrological cycle. Linear shape spectra are more frequent in flooding situations when nutrient input causes ...
Ripa Jörgen - - 2003
The densities of populations in a community or food web vary as a consequence of both population interactions and environmental (e.g. weather) fluctuations. Populations often respond to the same kinds of environmental fluctuations, and therefore experience correlated environments. Furthermore, some environmental factors change slowly over time, thereby producing positive environmental ...
Poitrineau K - - 2003
Although very common under natural conditions, the consequences of multiple enemies (parasites, predators, herbivores, or even 'chemical' enemies like insecticides) on investment in defence has scarcely been investigated. In this paper, we present a simple model of the joint evolution of two defences targeted against two enemies. We illustrate how ...
Zhang Yixin - - 2003
Energy and nutrient subsidies transported across ecosystem boundaries are increasingly appreciated as key drivers of consumer-resource dynamics. As purveyors of pulsed marine-derived nutrients (MDN), spawning salmon are one such cross-ecosystem subsidy to freshwaters connected to the north Pacific. We examined how salmon carcasses influenced detrital processing in an oligotrophic stream. ...
Tittel Jörg - - 2003
The majority of organisms can be grouped into those relying solely on photosynthesis (phototrophy) or those relying solely on the assimilation of organic substances (heterotrophy) to meet their requirements for energy and carbon. However, a special life history trait exists in which organisms combine both phototrophy and heterotrophy. Such "mixotrophy" ...
Fred R. Musser
Generalist predators are common in most agricultural cropping systems. However, pest control from these predators is often overlooked as a component of integrated pest management (IPM) because the extent of predation is generally unknown and difficult to assess. In western New York sweet corn (Zea mays L.), the primary predators ...
CHRISTOPHER M. PENNUTO
Invertebrate prey have been shown to select suboptimal resource patches in the face of predation (the food-predation risk trade-off). The foraging strategy used by a predator and the environmental context under which an interaction occurs potentially mediates prey responses to predators. Here, I determined whether season, predator presence or alternative ...
Binelli A - - 2003
Several models of varying complexity have been used to predict pollutant concentrations in the higher levels of the food web from those in lower levels, but the role of the biomagnification process in aquatic food chains is still controversial. We used the fugacity-based approach to verify the transfer of PCBs ...
Chowdhury Debashish - - 2003
We incorporate the generic hierarchical architecture of foodwebs into a "unified" model that describes both micro- and macroevolutions within a single theoretical framework. This model describes the microevolution in detail by accounting for the birth, ageing, and natural death of individual organisms as well as prey-predator interactions on a hierarchical ...
Boone Michelle D - - 2003
The effect of a contaminant on a community may not be easily predicted, given that complex changes in food resources and predator-prey dynamics may result. The objectives of our study were to determine the interactive effects of the insecticide carbaryl and predators on body size, development, survival, and activity of ...
Sinclair A R E - - 2003
There are many cases where animal populations are affected by predators and resources in terrestrial ecosystems, but the factors that determine when one or the other predominates remain poorly understood. Here we show, using 40 years of data from the highly diverse mammal community of the Serengeti ecosystem, East Africa, ...
Maeto Kaoru - - 2003
Quercus crispula (= Q. mongolica var. grosseserrata) is the predominant tree species in cool temperate, mixed broadleaf/conifer forests in northern Japan. We compared 11 years of data on acorn production in a population of Q. crispula, with data on seed-insect populations, to try to answer the following questions: (1) Does ...
Haspel Gal - - 2003
In this article, we provide direct evidence for injection of venom by a wasp into the central nervous system of its cockroach prey. Venomous predators use neurotoxins that generally act at the neuromuscular junction, resulting in different types of prey paralysis. The sting of the parasitoid wasp Ampulex compressa is ...
Tveraa Torkild - - 2003
A central issue in ecology is to what extent food limitation and predation affect animal populations. We studied how survival and reproductive success was related to the female's size in a population of semi-domesticated reindeer during 2 years where there was a large difference in snowfall during winter. The females ...
Fry B - - 2003
Mangrove forests are important coastal wetlands in most of the tropics, but their importance to fisheries is poorly understood. Rationales for conserving these ecosystems are partly based on ideas that mangroves are important to food webs that support fisheries. Here we review use of stable isotopes to test the strength ...
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