Search results for "Segregation"
showing 10 items of 100 documents
Dietary and Temporal Niche Differentiation in Tropical Ants-Can They Explain Local Ant Coexistence?
2014
How species with similar ecological requirements avoid competitive exclusion remains contentious, especially in the species-rich tropics. Niche differentiation has been proposed as a major mechanism for species coexistence. However, different niche dimensions must be studied simultaneously to assess their combined effects on diversity and composition of a community. In most terrestrial ecosystems, ants are among the most abundant and ubiquitous animals. Since they display direct, aggressive competition and often competitively displace subordinate species from resources, niche differentiation may be especially relevant among ants. We studied temporal and trophic niche differentiation in a gr…
Geographic Distribution and Niche Divergence of Two Stinkbugs,Parastrachia japonensisandParastrachia nagaensis
2014
Parastrachiidae is a small stinkbug family containing only one genus and two species, Parastrachia japonensis (Scott) (Hemiptera: Heteroptera: Pentatomoidea) and Parastrachia nagaensis Distant. The geographic distribution of the genus has been poorly studied. Niche conservatism refers to that idea that closely related species are more ecologically similar than would be expected, whereas niche divergence predicts they occupy distinct niche spaces. The existence of only two species within one genus suggests niche conservatism or differentiation might exist among them. Herein, the distribution of the genus was mapped, potential distributions were predicted using ecological niche modeling, and …
Segregated ice and liquefaction effects on compaction of fragipans
2004
The brittleness of fragipans is generally ascribed to the close-packing fabric arrangement acquired at the initial step of pedogenesis thanks to physical processes. However, there is an on-going debate over the agent causing soil densification. In this work, we tested the plausibility that ice segregation or liquefaction could have been the cause of the compaction of four fragipans. Two of them are located in nonseismic areas that have experienced periglacial conditions; one is from a strongly seismic area not affected by periglacial conditions, while the fourth site underwent moderate seismic activity and slight periglacial conditions. After disaggregation in the laboratory, soil specimens…
Jews under Islam in early modern Morocco in travel chronicles
2020
This paper addresses the relationship between the ideological and legal structures that discriminated against Jews in early modern Morocco and its reflection in social practices. The study shows th...
The high rate of endoreduplication in the repair deficient CHO mutant EM9 parallels a reduced level of methylated deoxycytidine in DNA
2008
It has been recently proposed that hypomethylation of DNA induced by 5-azacytidine (5-azaC) leads to reduced chromatid decatenation that ends up in endoreduplication, most likely due to a failure in topo II function [S. Mateos, I. Domínguez, N. Pastor, G. Cantero, F. Cortés, The DNA demethylating 5-azaC induces endoreduplication in cultured Chinese hamster cells, Mutat. Res. 578 (2005) 33-42]. The Chinese hamster mutant cell line EM9 has a high spontaneous frequency of endoreduplication as compared to its parental line AA8. In order to see if this is related to the degree of DNA methylation, we have investigated the basal levels of both endpoints in AA8 and EM9, as well as the effect of ext…
Cue combination in a combined feature contrast detection and figure identification task
2006
AbstractTarget figures defined by feature contrast in spatial frequency, orientation or both cues had to be detected in Gabor random fields and their shape had to be identified in a dual task paradigm. Performance improved with increasing feature contrast and was strongly correlated among both tasks. Subjects performed significantly better with combined cues than with single cues. The improvement due to cue summation was stronger than predicted by the assumption of independent feature specific mechanisms, and increased with the performance level achieved with single cues until it was limited by ceiling effects. Further, cue summation was also strongly correlated among tasks: when there was …
Geographic variability of ecological niches of plant species: are competition and stress relevant?
2002
A species’ niche position may differ strongly between geographic regions, for instance due to the effect of competitors or ecophysiological stress. However, it is unclear whether such strong geographic niche variation is the rule or the exception. We compared the niche positions of plant species between central England and eastern central Europe (as available from the literature), using phylogenetically independent contrasts. We found that most species occupied similar niche positions in both regions. More importantly, we found that niche variation was not higher in species susceptible to competitive displacement. Nor was niche variation higher in species that reach the edge of their range …
Niche segregation of coexisting Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) constrains food web coupling in subarctic lakes
2012
SUMMARY 1. Generalist fish species are recognised as important couplers of benthic and pelagic food-web compartments in lakes. However, interspecific niche segregation and individual specialisation may limit the potential for generalistic feeding behaviour. 2. We studied summer habitat use, stomach contents and stable isotopic compositions of the generalist feeder Arctic charr coexisting with its common resource competitor brown trout in five subarctic lakes in northern Norway to reveal population-level and individual-level niche plasticity. 3. Charr and trout showed partial niche segregation in all five lakes. Charr used all habitat types and a wide variety of invertebrate prey including z…
Urban segregation and unemployment: A case study of the urban area of Marseille – Aix-en-Provence (France)
2018
International audience; In this paper, we study the effects of the spatial organization of the urban area of Marseille – Aix-en-Provence on unemployment there. More specifically, differences in the characteristics of the residential population induce urban stratification with the result that urban structure may affect the probability of employment. In order to evaluate the effects of spatial structure on unemployment, we implement a spatial probit model to reveal the employment probabilities of young adults still living with their parents. Our results support the hypothesis that living in or near a deprived neighborhood decreases the probability of employment.
The oxidizing agent tertiary butyl hydroperoxide induces disturbances in spindle organization, c-meiosis, and aneuploidy in mouse oocytes
1996
It has been recently proposed that a concomitant generation of oxidative stress of oocytes with increasing maternal age may be a major factor responsible for the age-related increase in aneuploid conceptions. As a preliminary step in the testing of this hypothesis, we need to confirm that oxidative stress in itself can induce errors in chromosome segregation. In order to achieve this goal, germinal vesicle (GV)-stage mouse oocytes from unstimulated ICR and (C57BL x CBA) F1 hybrid female mice were matured in vitro for 9 h for metaphase I (MI) oocytes or 16 h for metaphase II (MII) oocytes in the presence of varying concentrations of the oxidizing agent tertiary-butyl hydroperoxide (tBH). MII…