Neutral Competition Research Articles

Phylogenetic community ecology needs to take positive interactions into account

Phylogenetic community ecology uses phylogenetic relationships among species to infer the dominant processes that shape community ecological structure. This field has particularly focused on habitat filtering and competition, the latter driving divergence and competitive exclusion. However, the effects of positive interactions among species of the same guild have rarely been considered in either empirical studies or theoretical models. We have recently documented a pervasive influence of mutualism in driving adaptive convergence in ecological niche. Müllerian mimicry in butterflies is one of the best studied examples of mutualism, where unpalatable species converge in wing pattern locally to advertise their toxicity to predators. We showed that species that share similar wing patterns are more similar in their ecology than expected given the phylogeny and co-exist at a fine spatial scale, thereby maximizing the warning signal to local predators. Evidence for competition was detected only among species with distinct wing patterns, implying that mutualistic interactions outweigh the effects competition. Positive interactions among potential competitors are common among plants and animals. We argue that such forces should be considered in the field of phylogenetic community ecology, alongside neutral processes, habitat filtering and competition.

Immigration history controls diversification in experimental adaptive radiation

Diversity in biological communities is a historical product of immigration, diversification and extinction, but the combined effect of these processes is poorly understood. Here we show that the order and timing of immigration controls the extent of diversification. When an ancestral bacterial genotype was introduced into a spatially structured habitat, it rapidly diversified into multiple niche-specialist types. However, diversification was suppressed when a niche-specialist type was introduced before, or shortly after, introduction of the ancestral genotype. In contrast, little suppression occurred when the same niche specialist was introduced relatively late. The negative impact of early arriving immigrants was attributable to the historically sensitive outcome of interactions involving neutral competition and indirect facilitation. Ultimately, the entire boom-and-bust dynamics of adaptive radiation were altered. These results demonstrate that immigration and diversification are tightly linked processes, with small differences in immigration history greatly affecting the evolutionary emergence of diversity.

Periodic solutions in higher-dimensional Lotka–Volterra neutral competition systems with state-dependent delays

Positive periodic solutions for two-dimensional neutral Lotka–Volterra system with state-dependent delays are considered by the theory of coincidence degree and some new techniques of computation. Applying this method for higher-dimensional system, we can also get more general conclusions and give many easy and verifiable conditions for some special cases of system by restricting its coefficients.

Positive periodic solution of a neutral delay competition model with impulses

Sufficient conditions are obtained for the existence of a periodic positive solution of the following neutral impulsive delay competition model Our results in this article indicate that under the appropriate linear periodic impulsive perturbations, the neutral impulsive delay competition system preserves the original periodicity of the neutral nonimpulsive delay competition system. In particular, our results are applied to the special nonimpulsive delay competition model and some known results are generalized.

A family of highly selective allosteric modulators of the metabotropic glutamate receptor subtype 5.

We have identified a family of highly selective allosteric modulators of the group I metabotropic glutamate receptor subtype 5 (mGluR5). This family of closely related analogs exerts a spectrum of effects, ranging from positive to negative allosteric modulation, and includes compounds that do not themselves modulate mGluR5 agonist activity but rather prevent other family members from exerting their modulatory effects. 3,3'-Difluorobenzaldazine (DFB) has no agonist activity, but it acts as a selective positive allosteric modulator of human and rat mGluR5. DFB potentiates threshold responses to glutamate, quisqualate, and 3,5-dihydroxyphenylglycine in fluorometric Ca2+ assays 3- to 6-fold, with EC50 values in the 2 to 5 microM range, and at 10 to 100 microM, it shifts mGluR5 agonist concentration-response curves approximately 2-fold to the left. The analog 3,3'-dimethoxybenzaldazine (DMeOB) acts as a negative modulator of mGluR5 agonist activity, with an IC50 of 3 microM in fluorometric Ca2+ assays, whereas the analog 3,3'-dichlorobenzaldazine (DCB) does not exert any apparent modulatory effect on mGluR5 activity. However, DCB seems to act as an allosteric ligand with neutral cooperativity, preventing the positive allosteric modulation of mGluRs by DFB as well as the negative modulatory effect of DMeOB. None of these analogs affects binding of [3H]quisqualate to the orthosteric (glutamate) site, but they do inhibit [3H]3-methoxy-5-(2-pyridinylethynyl)pyridine binding to the site for 2-methyl-6-(phenylethynyl)-pyridine, a previously identified negative allosteric modulator. With the use of these compounds, we provide evidence that allosteric sites on GPCRs can respond to closely related ligands with a range of pharmacological activities from positive to negative modulation as well as to neutral competition of this modulation.

Chaperone and antichaperone activities of trigger factor.

Reduced denatured lysozyme tends to aggregate at neutral pH and competition between productive folding and aggregation substantially reduces the efficiency of refolding. Trigger factor, a folding catalyst and chaperone can, depending on the concentration of trigger factor and the solution conditions, cause either a substantial increase (chaperone activity) or a substantial decrease (antichaperone activity) in the recovery of native lysozyme as compared with spontaneous refolding. When trigger factor is working as a chaperone, the reactivation rates of lysozyme are decelerated and aggregation decreases with increasing trigger factor concentrations. Under conditions where antichaperone activity of trigger factor dominates, the reactivation rates of lysozyme are accelerated and aggregation is increased. Trigger factor and lysozyme were both released from the aggregates on re-solubilization with urea indicating that trigger factor participates directly in aggregate formation and is incorporated into the aggregates. The apparently dual effect of trigger factor toward refolding of lysozyme is a consequence of the peptide binding ability and may be important in regulation of protein biosynthesis.

Periodic solution of a neutral delay competition model

In this paper, we use topological degree method to obtain the existence of a positive periodic solution of the neutral delay competition model % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiqabeqaamaabaabaaGcbaWaaiqaaqaabe% qaaiqadwhagaqbaiaacIcacaWG0bGaaiykaiabg2da9iaadkhadaWg% aaWcbaGaaGymaaqabaGccaGGOaGaamiDaiaacMcadaWadaqaaiaaig% dacqGHsislcaWGRbWaaSbaaSqaaiaaigdaaeqaaOGaaiikaiaadsha% caGGPaGaamyDaiaacIcacaWG0bGaaiykaiabgkHiTiaadggacaGGOa% GaamiDaiaacMcacaWG1bGaaiikaiaadshacqGHsislcaWGYbWaaSba% aSqaaiaaigdaaeqaaOGaaiykaiabgkHiTiabek7aIjaacIcacaWG0b% GaaiykaiqadwhagaqbaiaacIcacaWG0bGaeyOeI0IaeqiXdq3aaSba% aSqaaiaaicdaaeqaaOGaaiykaiabgkHiTiaadogadaWgaaWcbaGaaG% ymaaqabaGccaGGOaGaamiDaiaacMcacqaHfpqDcaGGOaGaamiDaiab% gkHiTiabes8a0naaBaaaleaacaaIYaaabeaakiaacMcaaiaawUfaca% GLDbaadaWgaaWcbaGaaiilaaqabaaakeaacuaHfpqDgaqbaiaacIca% caWG0bGaaiykaiabg2da9iaadkhadaWgaaWcbaGaaGOmaaqabaGcca% GGOaGaamiDaiaacMcacqaHfpqDcaGGOaGaamiDaiaacMcadaWadaqa% aiaaigdacqGHsislcaWGJbWaaSbaaSqaaiaaikdaaeqaaOGaaiikai% aadshacaGGPaGaamyDaiaacIcacaWG0bGaeyOeI0IaeqiXdq3aaSba% aSqaaiaaiodaaeqaaOGaaiykaiabgkHiTiaadUgadaWgaaWcbaGaaG% OmaaqabaGccaGGOaGaamiDaiaacMcacqaHfpqDcaGGOaGaamiDaiab% gkHiTiabes8a0naaBaaaleaacaaI0aaabeaakiaacMcaaiaawUfaca% GLDbaadaWgaaWcbaGaaiilaaqabaaaaOGaay5Eaaaaaa!9897! $$\left\{ \begin{gathered} u'(t) = r_1 (t)\left[ {1 - k_1 (t)u(t) - a(t)u(t - r_1 ) - \beta (t)u'(t - \tau _0 ) - c_1 (t)\upsilon (t - \tau _2 )} \right]_, \hfill \\ \upsilon '(t) = r_2 (t)\upsilon (t)\left[ {1 - c_2 (t)u(t - \tau _3 ) - k_2 (t)\upsilon (t - \tau _4 )} \right]_, \hfill \\ \end{gathered} \right.$$ where α, β, Γ{in1},k{in1},c{in1}k i, ci (i=1,2) are positive continuous ω-periodic functions and τ{inj} (j=0,1,…,4) are nonnegative constants.

Disturbance and neutral competition theory in rain forest dynamics

Subsequent to a disturbance in a tropical rain forest, many new stems arrive, either as new seedlings, previously established seedlings, small saplings, newly germinating seeds that were in the seed bank previously, or as newly germinating seeds that arrived after the disturbance. As the new stems grow, they eventually enter a stage of intense competition, at which point competitive thinning occurs. To describe the various patterns this process may take, a theoretical focus is proposed in which the neutrality of competition among different species of rain forest trees is assumed. Using the total biomass and total number of stems as state variables, the dynamic interaction between these two variables in the post hurricane forest is described. Using this model, six distinct patterns of post disturbance succession are recognized and discussed. Data from post hurricane succession in a tropical rain forest in Nicaragua are applied to one aspect of the theory.

Spectral and chemical evidence for the formation of zinc-porphyrin in aged, initially metal-free, porphyrin-ix solutions

The appearance of new additional bands, at 580 and 630 nm, in the fluorescence spectra of porphyrins, upon the aging of their aqueous solutions, was investigated for four porphyrin systems: The deutero, the hemato, the hemato-derivative, and the proto. The conditions for quantitative conversion to the new spectra were sought. To that end the concentration levels investigated were adjusted to have each porphyrin system in a monomer-dominant state. The species fluorescing at 580 nm was denoted f580 and its rate of appearance was found to fit firstorder kinetics, for each porphyrin, the range of the rate constants being 0.03–0.10 hr −1. Two key issues were probed: (a) The identity of f580, the effort directed towards zincporphyrin. (b) Its origins—a contaminant unmasked, or a species newly formed, during the aging. Testing f580 for zincporphyrin properties, spectral at neutral pH, acid/base de/remetalation, EDTA competition, and chromatography gave in each case positive results, allowing the identification of f580 as zincoporphyrin. On the basis of the data obtained and the known sources for the contamination of aqueous solutions by zinc, the case is made for zinc porphyrin formation upon aging. The relevance of the phenomena to the therapeutic activities of porphyrins is discussed.