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Critical Transition (critical + transition)
Selected AbstractsThe relationships between habitat topology, critical scales of connectivity and tick abundance Ixodes ricinus in a heterogeneous landscape in northern SpainECOGRAPHY, Issue 5 2003Agustin Estrada-Peña The habitat mosaic was used to quantify connectivity between patches of different tick density of the notorious tick species Ixodes ricinus in an attempt to determine the cause of variations in tick abundance among apparently homogeneous sites in northern Spain. The analysis revealed that patches with high tick abundance are "stepping-stone" territories that, when removed from the landscape, cause large changes in connectivity. Sites with medium tick abundance do not cause such a critical transition in connectivity. Patches with low tick abundance, but optimal abiotic conditions for survival, are located within the minimum cost corridors network joining the patches, while those sites where the tick has been intermittently collected are located at variable distances from this network. Sites where the tick is consistently absent, but where the habitat is predicted to be suitable (old, heterogeneous forests of Quercus spp.) for the tick, are very separated from this main network of connections. These results suggest that tick distribution in a zone is highly affected not only by abiotic variables (vegetation and weather) but also by host movements. Dispersal of the tick is a function of how the hosts perceive the habitat, and the habitat's permeability to host movement. Permanent tick populations seem to be supported by the existence of these critical, high density patches, located at significant places within the habitat network. [source] Testing for criticality in ecosystem dynamics: the case of Amazonian rainforest and savanna fireECOLOGY LETTERS, Issue 7 2010Salvador Pueyo Ecology Letters (2010) 13: 793,802 Abstract We test for two critical phenomena in Amazonian ecosystems: self-organized criticality (SOC) and critical transitions. SOC is often presented in the complex systems literature as a general explanation for scale invariance in nature. In particular, this mechanism is claimed to underlie the macroscopic structure and dynamics of terrestrial ecosystems. These would be inextricably linked to the action of fire, which is conceived as an endogenous ecological process. We show that Amazonian savanna fires display the scale-invariant features characteristic of SOC but do not display SOC. The same is true in Amazonian rainforests subject to moderate drought. These findings prove that there are other causes of scale invariance in ecosystems. In contrast, we do find evidence of a critical transition to a megafire regime under extreme drought in rainforests; this phenomenon is likely to determine the time scale of a possible loss of Amazonian rainforest caused by climate change. [source] The angiosperm radiation revisited, an ecological explanation for Darwin's ,abominable mystery'ECOLOGY LETTERS, Issue 9 2009Frank Berendse Abstract One of the greatest terrestrial radiations is the diversification of the flowering plants (Angiospermae) in the Cretaceous period. Early angiosperms appear to have been limited to disturbed, aquatic or extremely dry sites, suggesting that they were suppressed in most other places by the gymnosperms that still dominated the plant world. However, fossil evidence suggests that by the end of the Cretaceous the angiosperms had spectacularly taken over the dominant position from the gymnosperms around the globe. Here, we suggest an ecological explanation for their escape from their subordinate position relative to gymnosperms and ferns. We propose that angiosperms due to their higher growth rates profit more rapidly from increased nutrient supply than gymnosperms, whereas at the same time angiosperms promote soil nutrient release by producing litter that is more easily decomposed. This positive feedback may have resulted in a runaway process once angiosperms had reached a certain abundance. Evidence for the possibility of such a critical transition to angiosperm dominance comes from recent work on large scale vegetation shifts, linking long-term field observations, large scale experiments and the use of simulation models. [source] Overcoming the Effects of Variation in Infant Speech Segmentation: Influences of Word FamiliarityINFANCY, Issue 1 2008Leher Singh Previous studies have shown that 7.5-month-olds can track and encode words in fluent speech, but they fail to equate instances of a word that contrast in talker gender, vocal affect, and fundamental frequency. By 10.5 months, they succeed at generalizing across such variability, marking a clear transition period during which infants' word recognition skills become qualitatively more mature. Here we explore the role of word familiarity in this critical transition and, in particular, whether words that occur frequently in a child's listening environment (i.e., "Mommy" and "Daddy") are more easily recognized when they differ in surface characteristics than those that infants have not previously encountered (termed nonwords). Results demonstrate that words are segmented from continuous speech in a more linguistically mature fashion than nonwords at 7.5 months, but at 10.5 months, both words and nonwords are segmented in a relatively mature fashion. These findings suggest that early word recognition is facilitated in cases where infants have had significant exposure to items, but at later stages, infants are able to segment items regardless of their presumed familiarity. [source] Spanning the gap: experimental determination of paratenic host specificity of horsehair worms (Nematomorpha: Gordiida)INVERTEBRATE BIOLOGY, Issue 1 2003Ben Hanelt Abstract. Details of the life cycle of freshwater nematomorphs (gordiids) remain unclear. Free-living aquatic larval gordiids must make a critical transition from an epibenthic aquatic environment to terrestrial hosts. In order to identify potential hosts capable of bridging this ecological gap, the specificity of paratenic hosts of three common species of North American gordiids was investigated. All three species were characterized by an identical infection pattern: low host specificity. Gordiids were able to encyst within annelids, mollusks, crustaceans, insects and a vertebrate. Three species of putative host (a turbellarian, a water mite, and a mosquito larva) were not infected with any of the gordiid species. Internal defense reactions (IDR) and feeding behaviors are implicated as preventing infection in these species. Several of the other host species produced either an IDR or an immune reaction to the cysts, although reactions to the cysts were highly variable between species. In most species, IDR did not cause noticeable harm to the encysted larvae. It is proposed that although many species are easily infected with gordiid cysts, most do not act as natural paratenic hosts. For some of these host groups, especially snails, a role as reservoir host is suggested. Of all hosts included in this study, aquatic insects were identified as the hosts likely responsible for spanning the ecological gap and acting as true hosts for gordiids. [source] A finite element-based approach for whole-system simulation of packaging systems for their improved design and operationPACKAGING TECHNOLOGY AND SCIENCE, Issue 4 2009Ben James Hicks Abstract The introduction of legislation to minimize packaging waste requires consumer goods manufacturers to use lighter-weight materials and increase the use of recycled materials. This is demanding that machinery manufacturers provide highly flexible machines and tooling capable of handling these materials and new package designs. However, the ability of manufacturers to achieve this is all but prevented by a lack of fundamental understanding of machine,material interactions and an ability to generate such understanding. One way to overcome this is to use advanced simulation tools to represent the whole system including machine, process, materials and product. A finite element-based simulation has been created to represent the in-process behaviour of a packing system. The simulation focuses on the critical transition between flattened and erected states of a carton. In order to successfully simulate such a complex process, there are a number of major challenges concerning the representation of packaging materials and their properties, changing material behaviour during processing, machinery simulation and process modelling (simulating the interfacial interactions that take place during processing). The application of the whole-system simulation for the purposes of improved design and operation are discussed with respect to four activities: design and set-up of tooling, determination of optimal process settings, specification of material properties and the design of the pack. In all cases, a strong correlation was observed between the theoretical results and those obtained practically, thereby enabling quantitative understanding and quantitative rules to be generated. Copyright © 2009 John Wiley & Sons, Ltd. [source] The influence of heightened body-awareness on walking through aperturesAPPLIED COGNITIVE PSYCHOLOGY, Issue 4 2010Stacy Lopresti-Goodman The reported study measured the ratio between aperture-width and hip-width that marked the critical transition from frontal walking to body rotation for male and female participants. Half of the participants of each sex wore form-fitting lycra clothes and half loose-fitting jogging suits. Participants wearing the form-fitting clothing reported heightened body awareness relative to those wearing the loose-fitting clothing. For male participants this difference was reflected in a smaller aperture-to-hip ratio in the form-fitting than loose-fitting clothing condition. That is, males walked frontally through smaller apertures when wearing form-fitting than when wearing loose-fitting clothing. For females there was no difference in walking action as a function of clothing style. Results are discussed in terms of the perception of action opportunities in the environment, the influence of body awareness on such perception and sex differences. Copyright © 2009 John Wiley & Sons, Ltd. [source] Testing for criticality in ecosystem dynamics: the case of Amazonian rainforest and savanna fireECOLOGY LETTERS, Issue 7 2010Salvador Pueyo Ecology Letters (2010) 13: 793,802 Abstract We test for two critical phenomena in Amazonian ecosystems: self-organized criticality (SOC) and critical transitions. SOC is often presented in the complex systems literature as a general explanation for scale invariance in nature. In particular, this mechanism is claimed to underlie the macroscopic structure and dynamics of terrestrial ecosystems. These would be inextricably linked to the action of fire, which is conceived as an endogenous ecological process. We show that Amazonian savanna fires display the scale-invariant features characteristic of SOC but do not display SOC. The same is true in Amazonian rainforests subject to moderate drought. These findings prove that there are other causes of scale invariance in ecosystems. In contrast, we do find evidence of a critical transition to a megafire regime under extreme drought in rainforests; this phenomenon is likely to determine the time scale of a possible loss of Amazonian rainforest caused by climate change. [source] What are the high risk periods for incident substance use and transitions to abuse and dependence?INTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue S1 2008Implications for early intervention, prevention Abstract Background: For a better understanding of the evolution of addictive disorders and the timely initiation of early intervention and prevention, we have to learn when and how quickly the critical transitions from first substance use (SU) to regular use and from first SU and regular SU to abuse and dependence occur. Little data are currently available on the transitions to substance use disorders (SUDs) across the spectrum of legal and illegal drugs taking into account gender differences. It is the aim of this paper to describe the high density incidence and transition periods of SU and SUD for alcohol, nicotine, cannabis and other illicit drugs for young males and females. Methods: A sample of (N = 3021) community subjects aged 14,24 at baseline were followed-up prospectively over 10-years. SU and SUD were assessed using the DSM-IV/M-CIDI. Results: Ages 10,16 are the high risk period for first alcohol and nicotine use (up to 38% of subjects start before age 14). Onset of illegal SU occurs later. Substantial proportions of transitions to regular SU and SUD occur in the first three years after SU onset. Only few gender differences were found for time patterns of SU/SUD incidence and transition. Conclusion: Except for alcohol the time windows for targeted intervention to prevent progression to malignant patterns in adolescence are critically small, leaving little time for targeted intervention to prevent transition. The fast transitions to abuse and dependence in adolescence may be indicative for the increased vulnerability to substance effects in this time period. Basic research on the determinants of transitions should thus target this period in adolescence. Copyright © 2008 John Wiley & Sons, Ltd. [source] | |||||||||||||