915 resultados para Coexistence. H Pectoralis. H Sellowi. Maxent. ENFA. Competition. Niche Conservatism
Resumo:
This paper was published in the highly respected, peer reviewed and ISI ranked journal - 'European Integration on-line paper series
Fragmentation of metastable SF6−* ions with microsecond lifetimes in competition with autodetachment
Resumo:
Fragmentation of metastable SF6-* ions formed in low energy electron attachment to SF6has been investigated. The dissociation reaction SF6-*?SF5-+F has been observed ~ 1.5–3.4 µs and ~ 17–32 µs after electron attachment in a time-of-flight and a double focusing two sector field mass spectrometer, respectively. Metastable dissociation is observed with maximum intensity at ~ 0.3 eV between the SF6-* peak at zero and theSF5- peak at ~ 0.4 eV. The kinetic energy released in dissociation is low, with a most probable value of 18 meV. The lifetime of SF6-* decreases as the electron energy increases, but it is not possible to fit this decrease with statistical Rice–Ramsperger–Kassel/quasiequilibrium theory. Metastable dissociation of SF6-* appears to compete with autodetachment of the electron at all electron energies.
Resumo:
Clustering analysis of data from DNA microarray hybridization studies is an essential task for identifying biologically relevant groups of genes. Attribute cluster algorithm (ACA) has provided an attractive way to group and select meaningful genes. However, ACA needs much prior knowledge about the genes to set the number of clusters. In practical applications, if the number of clusters is misspecified, the performance of the ACA will deteriorate rapidly. In fact, it is a very demanding to do that because of our little knowledge. We propose the Cooperative Competition Cluster Algorithm (CCCA) in this paper. In the algorithm, we assume that both cooperation and competition exist simultaneously between clusters in the process of clustering. By using this principle of Cooperative Competition, the number of clusters can be found in the process of clustering. Experimental results on a synthetic and gene expression data are demonstrated. The results show that CCCA can choose the number of clusters automatically and get excellent performance with respect to other competing methods.
Resumo:
We present a synthesis of empirical and theoretical work investigating how parasites influence competitive and predatory interactions between other species. We examine the direct and indirect effects of parasitism and discuss examples of density and parasite-induced trait-mediated effects. Recent work reveals previously unrecognized complexity in parasite-mediated interactions. In addition to parasite-modified and apparent competition leading to species exclusion or enabling coexistence, parasites and predators interact in different ways to regulate or destablize the population dynamics of their joint prey. An emerging area is the impact of parasites on intraguild predation (IGP). Parasites can increase vulnerability of infected individuals to cannibalism or predation resulting in reversed species dominance in IGP hierarchies. We discuss the potential significance of parasites for community structure and biodiversity, in particular their role in promoting species exclusion or coexistence and the impact of emerging diseases. Ongoing invasions provide examples where parasites mediate native/invader interactions and play a key role in determining the outcome of invasions. We highlight the need for more quantitative data to assess the impact of parasites on communities, and the combination of theoretical and empirical studies to examine how the effects of parasitism scale up to community-level processes.
Resumo:
Studies of biological invasions predominantly stress threats to biodiversity through the elimination and replacement of native species. However, we must realise that resident communities may often be capable of integrating invaders, leading to patterns of coexistence. Within the past ninety years, three freshwater amphipod species have invaded Northern Ireland the North American Gammarus tigrinus and Crangonyx pseudogracilis, plus the European G. pulex. These species have come into contact with the ubiquitous native species, G. duebeni celticus. This study examined spatiotemporal patterns of stability of single and mixed species assemblages in an invaded lake. Lough Beg and its associated rivers were surveyed in summer 1994 and winter 1995, and a selection of stations re-sampled in summer one and five years later. All possible combinations of the four amphipod species were found. Although species presence/absence was stable between seasons at the scale of the whole lough, it was extremely fluid at the scale of individual sites, 82% of which changed in species composition between seasons. Overall mean amphipod abundance was similar across 5 distinguishable habitat types, but there were differences in species compositions among these habitats. In addition, although co-occurrences of Gammarus species did not differ from random, there was a strong negative association between Gammarus spp. and C. pseudogracilis. This latter pattern was at least in part generated by the better tolerance of C. pseudogracilis to lower water quality. A review of previous studies indicates that the exclusion of C. pseudogracilis by Gammarus species from high water quality areas is likely to involve biotic interaction. Thus, overall, co-existence of the four species, which is clearly dynamic and scale-dependent, appears promoted by spatial and temporal habitat heterogeneity. However, biotic interactions may also play a role in local exclusions. Since the three introduced species have not eliminated the native species, and each successive invasion has not replaced the previous invader, this study demonstrates that freshwater invaders may integrate with native communities leading to coexistence and increased species diversity.
Resumo:
Ammonia synthesis on three metal surfaces (Zr, Ru, and Pd) is investigated using density functional theory calculations. In addition to N-2 dissociation, all the transition states of the hydrogenation reactions from N to NH3 are located and the reaction energy profiles at both low and high surface coverages are compared and analyzed. The following are found: (i) Surface coverage effect on dissociation reactions is more significant than that on association reactions. (ii) The difference between N and H chemisorption energies, the so-called chemisorption energy gap which is a measure of adsorption competition, is vital to the reactivity of the catalysts. (iii) The hydrogenation barriers can considerably affect the overall rate of ammonia synthesis. A simple model to describe the relationship between dissociation and association reactions is proposed. (c) 2007 American Institute of Physics.
Resumo:
Political commentators often cast religious con? ict as the result of the numerical growth and political rise of a single faith. When Islam is involved, arguments about religious fundamentalism are quick to surface and often stand as an explanation in their own right. Yet, as useful as this type of explanation may be, it usually fails to address properly, if at all, two sets of important issues. It avoids, Ž rst, the question of the rise of other religions and their contribution to tensions and con? icts. Second, it reduces the role of the State to a reactive one. The State becomes an object of contest or conquest, or it is simply ignored. Adopting a different approach, this article investigates a controversy that took place in Mozambique in 1996 around the ‘ofŽ cialisation’ of two Islamic holidays. It looks at the role played by religious competition and state mediation. The article shows that the State’s abandonment of religious regulation – the establishment of a free ‘religious market’ – fostered religious competition that created tensions between faiths. It suggests that strife ensued because deregulation was almost absolute: the State did not take a clear stand in religious matters and faith organisations started to believe that the State was becoming, or could become, confessional. The conclusion discusses theoretical implications for the understanding of religious strife as well as Church and State relations. It also draws some implications for the case of Mozambique more speciŽ cally, implications which should have relevance for countries such as Malawi, Zambia and Zimbabwe where problems of a similar nature have arisen.