The Experts below are selected from a list of 135453 Experts worldwide ranked by ideXlab platform
Janneche Utne Skaare - One of the best experts on this subject based on the ideXlab platform.
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biomagnification of organochlorines along a barents sea Food Chain
Environmental Pollution, 2001Co-Authors: Katrine Borga, Geir W Gabrielsen, Janneche Utne SkaareAbstract:To trace the biomagnification of organochlorines in marine Food Chains near Svalbard, which may lead to the high organochlorine concentrations in top predators from the area, we compared concentrations and patterns of organochlorines in selected taxa. The pelagic crustaceans, Calanus spp. (copepods), Thysanoessa spp. (euphausiids), Parathemisto libellula (amphipod), and the fish species, Boreogadus saida (polar cod) and Gadus morhua (cod) were selected to represent the lower trophic levels in the Food web. Four seabird species were chosen at the higher trophic levels, Uria lomvia (Brunnich's guillemot), Cepphus grylle (black guillemot), Rissa tridactyla (black-legged kittiwake) and Larus hyperboreus (glaucous gull). We found low concentrations of the organochlorines Σhexachlorocyclohexanes (ΣHCHs), hexachlorobenzene (HCB), ΣChlordanes, ΣDDTs and Σpolychlorinated biphenyls (ΣPCBs) in crustaceans (11–50 ng g−1 lipid wt.) and fish (15–222 ng g−1 lipid wt.). In seabirds, the organochlorine concentrations biomagnified one to three orders of magnitude dependent on species and compound class. Glaucous gulls had the highest concentrations of all organochlorines. The organochlorine levels in all taxa except glaucous gull were comparable to those recorded in similar species in the Canadian Arctic. The organochlorine pattern changed from crustaceans and fish to seabirds. Moving up the Food Chain, the relative contribution of ΣHCHs, HCB and ΣChlordanes decreased, and the relative contribution of ΣDDTs, ΣPCBs, persistent compounds and metabolites increased. The results reflected trophic transfer of organochlorines along the Food Chain as well as different elimination potentials due to direct diffusion in crustaceans and fish, and higher contaminant metabolic activity in seabirds.
Thomas M Powell - One of the best experts on this subject based on the ideXlab platform.
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chaos in a three species Food Chain
Ecology, 1991Co-Authors: Alan Hastings, Thomas M PowellAbstract:A continuous time model of a Food Chain incorporating nonlinear functional (and numerical) responses exhibits chaotic dynamics in long-term behavior when biolog- ically reasonable parameter values are chosen. The appearance of chaos in this model suggests that chaotic dynamics may be common in natural Food webs.
Oren Etzioni - One of the best experts on this subject based on the ideXlab platform.
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moving up the information Food Chain deploying softbots on the world wide web
Ai Magazine, 1997Co-Authors: Oren EtzioniAbstract:I view the World Wide Web as an information Food Chain. The maze of pages and hyperlinks that comprise the Web are at the very bottom of the Chain. The WEBCRAWLERs and ALTAVISTAs of the world are information herbivores; they graze on Web pages and regurgitate them as searchable indices. Today, most Web users feed near the bottom of the information Food Chain, but the time is ripe to move up. Since 1991, we have been building information carnivores, which intelligently hunt and feast on herbivores in UNIX, on the Internet, and on the Web. Information carnivores will become increasingly critical as the Web continues to grow and as more naive users are exposed to its chaotic jumble.
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moving up the information Food Chain deploying softbots on the world wide web
National Conference on Artificial Intelligence, 1996Co-Authors: Oren EtzioniAbstract:I view the World Wide Web as an information Food Chain (figure 1). The maze of pages and hyperlinks that comprise the Web are at the very bottom of the Chain. The WebCrawlers and Alta Vistas of the world are information herbivores; they graze on Web pages and regurgitate them as searchable indices. Today, most Web users feed near the bottom of the information Food Chain, but the time is ripe to move up. Since 1991, we have been building information carnivores, which intelligently hunt and feast on herbivores in Unix (Etzioni, Lesh, & Segal 1993), on the Internet (Etzioni & Weld 1994), and on the Web (Doorenbos, Etzioni, & Weld 1996; Selberg & Etzioni 1995; Shakes, Langheinrich, & Etzioni 1996).
David M. Post - One of the best experts on this subject based on the ideXlab platform.
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Effects of productivity, disturbance, and ecosystem size on Food-Chain length: insights from a metacommunity model of intraguild predation
Ecological Research, 2012Co-Authors: Gaku Takimoto, David M. Post, David A. Spiller, Robert D. HoltAbstract:Traditionally, productivity and disturbance have been hypothesized as important determinants of Food-Chain length. More recently, growing empirical evidence suggests a strong role of ecosystem size. To theoretically explore the effects of basal productivity, disturbance, and ecosystem size on Food-Chain length, we develop and analyze a metacommunity model of intraguild predation (IGP). The model finds that, when local IGP is weak, increasing basal productivity, weakening disturbance, and increasing ecosystem size will generally increase Food-Chain length. When local IGP is strong, by contrast, increasing basal productivity or weakening disturbance favors intraguild predators and hinders the coexistence of intraguild predators and intraguild prey, limiting Food-Chain length. In contrast, increasing ecosystem size can promote coexistence even when local IGP is strong, increasing Food-Chain length through inserting intraguild prey and changing the degree of omnivory by intraguild predators. Intraguild prey needs to be the superior colonizer to intraguild predators for this to occur. We discuss that these theoretical predictions appear consistent with empirical patterns.
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Environmental determinants of Food-Chain length: a meta-analysis
Ecological Research, 2012Co-Authors: Gaku Takimoto, David M. PostAbstract:Food-Chain length is an important character of ecological communities that affects many of their functional aspects. Recently, an increasing number of studies have tested the effects of productivity, disturbance, or ecosystem size on Food-Chain length in a variety of natural systems. Here we conduct a formal meta-analysis to summarize findings from these empirical studies. We found significant positive mean effects of productivity and ecosystem size but no significant mean effect of disturbance on Food-Chain length. The strength of mean effect sizes was not significantly different between productivity and ecosystem size. These results lend general support to previous theories predicting the effect of productivity and ecosystem size, but fail to support the prediction that disturbance shortens Food Chains. In addition, our meta-analysis found that the effect sizes of primary studies were significantly heterogeneous for ecosystem size and disturbance, but not for productivity. This pattern might reflect that ecosystem size and disturbance can affect Food-Chain length through multiple different mechanisms, while productivity influences Food-Chain length in a simple manner through energy limitation.
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AN EXPERIMENTAL DISTURBANCE ALTERS FISH SIZE STRUCTURE BUT NOT Food Chain LENGTH IN STREAMS
Ecology, 2008Co-Authors: Annika W. Walters, David M. PostAbstract:Streams experience frequent natural disturbance and are undergoing considerable anthropogenic disturbance due to dam construction and water diversion. Disturbance is known to impact community structure, but its effect on Food Chain length is still a matter of considerable debate. Theoretical models show that longer Food Chains are less resilient to disturbance, so Food Chain length is predicted to be shorter following a disturbance event. Here we experimentally test the effect of disturbance on Food Chain length in streams by diverting stream flow. We found that our experimental low-flow disturbance did not alter Food Chain length. We did see an effect on body-size structure in our Food webs suggesting that Food Chain length may be an insensitive indicator of disturbance. We suggest that habitat heterogeneity and Food web complexity buffer the effect of disturbance on Food Chain length. The theoretical predictions of disturbance on Food Chain length are only likely to be seen in homogeneous systems that closely approximate the linear Food Chains the models are based upon.
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ECOSYSTEM SIZE, BUT NOT DISTURBANCE, DETERMINES Food‐Chain LENGTH ON ISLANDS OF THE BAHAMAS
Ecology, 2008Co-Authors: Gaku Takimoto, David A. Spiller, David M. PostAbstract:Ecologists have long struggled to explain variation in Food-Chain length among natural ecosystems. Food-Chain length is predicted to be shorter in ecosystems subjected to greater disturbance because longer Chains are theoretically less resilient to perturbation. Moreover, Food-Chain length is expected to be longer in larger ecosystems because increasing ecosystem size increases species richness and stabilizes predator-prey interactions, or increases total resource availability. Here we test the roles of disturbance and ecosystem size in determining the Food-Chain length of terrestrial Food webs on Bahamian islands. We found that disturbance affected the identity of top predators, but did not change Food-Chain length because alternative top predators occupied similar trophic positions. On the other hand, a 106 fold increase in ecosystem size elevated Food-Chain length by one trophic level. We suggest that the effect of disturbance on Food-Chain length is weak when alternate top predators are trophic omnivores and have similar trophic positions. This and previous work in lakes suggest that ecosystem size may be a strong determinant of Food-Chain length in both aquatic and terrestrial ecosystems.
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Proximate structural mechanisms for variation in Food-Chain length
Oikos, 2007Co-Authors: David M. Post, Gaku TakimotoAbstract:Food-Chain length is a central characteristic of ecological communities because of its strong influence on community structure and ecosystem function. While recent studies have started to better clarify the relationship between Food-Chain length and environmental gradients such as resource availability and ecosystem size, much less progress has been made in isolating the ultimate and proximate mechanisms that determine Food-Chain length. Progress has been slow, in part, because research has paid little attention to the proximate changes in Food web structure that must link variation in Food-Chain length to the ultimate dynamic mechanism. Here we outline the structural mechanisms that determine variation in Food-Chain length. We explore the implications of these mechanisms for understanding how changes in Food-web structure influence Food-Chain length using both an intraguild predation community model and data from natural ecosystems. The resulting framework provides the mechanisms for linking ultimate dynamic mechanisms to variation in Food-Chain length. It also suggests that simple linear Food-Chain models may make misleading predictions about patterns of variation in Food-Chain length because they are unable to incorporate important structural mechanisms that alter Food-web dynamics and cause non-linear shifts in Food-web structure. Intraguild predation models provide a more appropriate theoretical framework for understanding Food-Chain length in most natural ecosystems because they accommodate all of the proximate structural mechanisms identified here.
Alan Hastings - One of the best experts on this subject based on the ideXlab platform.
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chaos in a three species Food Chain
Ecology, 1991Co-Authors: Alan Hastings, Thomas M PowellAbstract:A continuous time model of a Food Chain incorporating nonlinear functional (and numerical) responses exhibits chaotic dynamics in long-term behavior when biolog- ically reasonable parameter values are chosen. The appearance of chaos in this model suggests that chaotic dynamics may be common in natural Food webs.