Coexistence in a simple food chain with diffusion

We show the global existence of classical positive solutions in each component of a Lotka-Volterra system with diffusion and logistic growing conditions. We are mainly interested in the search of coexistence states solving the associated elliptic problem under homogeneous Dirichlet boundary conditions.     

Differential utilization of space and food by the inshore rockfishes (Scorpaenidae: Sebastes) of Carmel Bay,California

Synopsis Six rockfish species were found to be common in the Carmel Bay kelp forests. Five of these occupy spatial zones that are more or less distinct from one another. Three species (S. atrovirens, S. chrysomelas, and S. carnatus) occupy species-specific spatial zones while two others (S. serranoides and S. melanops), although spatially distinct from each other, occupy zones that overlap completely with a sixth species, S. mystinus. Food overlap values (PSI) indicate that S. mystinus has low competitive overlap with all other species, and hence can coexist with two species using the same habitat. Dietary arrays reflect the distinct spatial zones occupied by most of the rockfishes. Structural characteristics associated with feeding (maxillary, intestine, and gill raker length) suggest that these species are differentially adapted in regard to feeding morphology. The coexistence of these rockfishes appears to be the result of the partitioning of food and space resources, rather than the result of stochastic events which appear to be important in the structuring of some coral-reef fish communities. S. mystinus juveniles represent a major trophic link between adult piscivores and the planktonic organisms upon which the juveniles feed. A sustained crash in S. mystinus numbers might have a negative effect on abundance of kelp forest piscivorous species.     

Molecular evolution as a process of message refinement

Summary Amino acid sequences are often said to code for proteins. Taking that statement literally, we propose a methodology in which protein sequences appear as messages and as such are amenable to the techniques of signal analysis. Not only does this view of amino acid sequences as messages appear to be tenable, but the clarity of expression of these sequences seems to increase, i.e., the noisiness decreases, consonant with notions of ascendancy in the hierarchy of morphological taxonomy.     

Palearctic passerines in Afrotropical environments: a review

Previous ecological studies of Palearctic passerine migrants in Africa have claimed to reveal some general features with respect to habitat use, foraging ecology and interspecific relationships with Afrotropical residents. In this review we discuss apparent contradictions between earlier generalisations and more recent results from more detailed field studies and explore in which areas our ecological knowledge and theoretical understanding remain poor and have given rise to misconceptions. For example, it has been claimed that migrants use structurally more diverse and open habitats and that they forage higher and in more peripheral parts of the vegetation than their ecologically similar Afrotropical counterparts, yet in the past these characteristics were often not clearly defined and not always correlated in practice. It has also been stated that migrants are more flexible in habitat use, occupying a wider range of habitat types and employing a higher diversity of foraging techniques, both of which were assumed to be adaptations to permit coexistence with Afrotropical residents by using untapped resources that are only seasonally available. Yet results from studies of the role of competition in shaping migrant-resident communities remain largely unconvincing. While flexibility may facilitate migrant-resident coexistence, it may also favour the evolution of migration because specialists are less able to use their advantages in different environments. We note that definitions of flexibility and specialisation may themselves depend on the ecological or evolutionary approach adopted by researchers. We conclude that few generalisations can safely be made about the ecology of Palearctic migrants in Africa and that adaptive explanations for the behaviours observed are largely lacking, as are studies of the fitness consequences of different migrant strategies such as have been conducted in the Nearctic-Neotropical migration system.     

Culture universals and genes

The Western idea of culture is built in opposition to that of nature. Among anthropologist the culture is a complex whole which includes knowledge, belief, law, custum and any capabilities and habits acquired by man as a member of society. The human specificity of culture is now openly discussed, the idea of an envolved structural base to behaviour is more admitted by the community of scientist but the question of an hereditary base to cultural traits is still unsolved.     

Effects of water potential and solute on the growth and interactions of two fungal symbionts of the mountain pine beetle

We investigated the effect of water potential (WP) on the growth of, and interaction between, two ophiostomatoid fungi, Grosmannia clavigera and Ophiostoma montium, associated with the mountain pine beetle (Dendroctonus ponderosae). The WP of malt extract agar was amended by adding potassium chloride (KCl) or sucrose. Growth of both fungi decreased with WP on KCl-amended media. Growth of G. clavigera also decreased with WP on sucrose-amended media, although growth was stimulated on these media compared to unamended treatments. Growth of O. montium remained relatively constant on sucrose-amended media, confounding the effect of WP on this species. Both fungi were able to colonize media occupied by the other species, but at a slower rate than on unoccupied media, indicating competition. In most treatments, G. clavigera grew faster than O. montium and colonized a greater area when the two fungi were inoculated concurrently but distant to one another on a Petri dish. However, when each fungus was inoculated adjacent to a 10-d-old well-established colony of the other species, O. montium colonized occupied media more effectively than G. clavigera considering the growth rate of each species alone. Thus, G. clavigera dominated primary (uncolonized) resources on most media, whereas O. montium was more effective in colonizing secondary (occupied) resources. The differential response of the two fungi to sucrose indicates that they may use different carbon sources, or use different carbon sources at different rates, in the tree. Fine-scale resource partitioning, differences in primary and secondary resource capture abilities, and the non-equilibrium dynamics in an attacked tree over time, could all act to promote the co-existence of two unit-restricted dispersers on a discontinuous resource.     

Typostrophism in Palaeozoic Ammonoids?

The anti-Darwinian “Typostrophe Theory” of O.H.Schindewolf can be put to the test by revisiting the ammonoid examples on which this macroevolutionary model was founded. It is shown that none of the three theoretical elements saltationism, internalism, and cyclism can be supported by empirical data obtained from ammonoid research. Putative saltations (“Typogenesis”) were feigned because of the lack of knowledge of intermediate forms. Internalistic and orthogenetic development (“Typostasis”) can only be favoured by neglecting possible functions of morphological characters. Preprogrammed extinction of “degenerated” clades (“Typolysis”) is unlikely when ruling out anthropocentric views regarding ammonoid morphology. In terms of evolution of Palaeozoic ammonoids, there is no basis for the preference of the “Typostrophe Theory” or some of its composing elements, including the “Type Concept” and “Proterogenesis”, over the Darwinian evolutionary model and the Modern Synthesis.      

New light on phosphate transfer from triesters

The reactivity of triesters is discussed in the general context of phosphate transfer, as usually studied for the reactions of mono- and diesters. Systematic work has typically concentrated on the Linear Free Energy Relationships measuring the dependence of reactivity on the nucleophile and the leaving group, but new results indicate that it can depend equally strongly on the two non-leaving (sometimes known as spectator) groups. This conclusion is supported by first results from theoretical calculations: which also predict that a two-step mechanism can be favored over a concerted S_N2(P) mechanism even for reactions involving leaving groups as good as p-nitrophenolate. This article is part of a Special Issue entitled: Chemistry and mechanism of phosphatases, diesterases and triesterases.     

Reduction of 1,4-quinone and Ubiquinones by Hydrogen Atom Transfer under UVA Irradiation

1,4-Benzoquinone, coenzyme Q 0 and Q 10 were reacted with a series of hydrogen donors in the ESR cavity in the presence or absence of UVA irradiation. The signals of the radicals generated from the hydrogen donors or of those of the semiquinones were detected. The reaction mechanism was interpreted by a hydrogen atom transfer instead of the usual electron transfer mechanism on the basis of the redox potentials of the reactants and the Marcus theory. The hydrogen atom transfer is explained by the excited triplet state of quinones, which, on the basis of quantum mechanic calculations, may be reached even under visible light. In some cases, hydrogen atom transfer was also observed without irradiation, although to a lesser extent.