Aluísio Pinheiro

NETWORK ANALYSIS REVEALS CONTRASTING EFFECTS OF INTRASPECIFIC COMPETITION ON INDIVIDUAL VS. POPULATION DIETS

Optimal foraging theory predicts that individuals should become more opportunistic when intraspecific competition is high and preferred resources are scarce. This density-dependent diet shift should result in increased diet breadth for individuals as they add previously unused prey to their repertoire. As a result, the niche breadth of the population as a whole should increase. In a recent study, R. Svanbäck and D. I. Bolnick confirmed that intraspecific competition led to increased population diet breadth in threespine stickleback (Gasterosteus aculeatus). However, individual diet breadth did not expand as resource levels declined. Here, we present a new method based on complex network theory that moves beyond a simple measure of diet breadth, and we use the method to reexamine the stickleback experiment. This method reveals that the population as a whole added new types of prey as stickleback density was increased. However, whereas foraging theory predicts that niche expansion is achieved by individuals accepting new prey in addition to previously preferred prey, we found that a subset of individuals ceased to use their previously preferred prey, even though other members of their population continued to specialize on the original prey types. As a result, populations were subdivided into groups of ecologically similar individuals, with diet variation among groups reflecting phenotype-dependent changes in foraging behavior as prey density declined. These results are consistent with foraging theory if we assume that quantitative trait variation among consumers affects prey preferences, and if cognitive constraints prevent individuals from continuing to use their formerly preferred prey while adding new prey.

Decomposability of high-dimensional diversity measures: Quasi-U-statistics, martingales and nonstandard asymptotics

In analyses of complex diversity, especially that arising in genetics, genomics, ecology and other high-dimensional (and sometimes low-sample-size) data models, typically subgroup decomposability (analogous to ANOVA decomposability) arises. For group divergence of diversity measures in a high-dimension low-sample-size scenario, it is shown that Hamming distance type statistics lead to a general class of quasi-U-statistics having, under the hypothesis of homogeneity, a martingale (array) property, providing a key to the study of general (nonstandard) asymptotics. Neither the stochastic independence nor homogeneity of the marginal probability laws plays a basic role. A genomic MANOVA model is presented as an illustration.

Differential aluminium-impaired nutrient uptake along the root axis of two maize genotypes contrasting in resistance to aluminium

Background and aimsThe sensitivity of root cells and root processes to toxic aluminium ions (Al3+) varies along the root axis. This study was established to assess the sensitivity of nutrient uptake to Al along the main root axis of maize genotypes that differ in resistance to Al and to test whether citrate, an Al-complexing compound that is unevenly released along the root axis, can play a role in protecting the root from Al-impaired nutrient uptake.MethodsA divided-root-chamber technique was used to measure net fluxes of calcium (Ca2+), magnesium (Mg2+), and potassium (K+) along intact roots of two maize genotypes differing in resistance to Al. The accumulation of Al along their main root axis was also measured in short-term experiments. Results of these experiments were compared with those of a previous study, where citrate exudation had been measured along identical maize root axes.ResultsAluminium affected nutrient uptake widely along the root with strong effects in the apical region, reducing total Ca2+ and Mg2+ uptake, but not K+ uptake. The negative effects of Al3+ were more pronounced in the Al sensitive genotype than in the resistant one. The former also accumulated more Al in its roots than the latter, but this differential accumulation was observed only in the apical part of the root. The spatial pattern of nutrient uptake, irrespective of Al treatment, did not match that of Al-stimulated citrate exudation.ConclusionBased on the differential sensitivity of the root axis of the two maize genotypes and especially on the extent of the root zones where these differences are expressed, it is suggested that the less Al-disturbed nutrient uptake of a genotype is associated with its resistance to Al.

An asymptotically normal test for the selective neutrality hypothesis

An important parameter in the study of population evolution is

Parametric Modelling Of Genomic Sequences Distance

\theta=4N\nu

Self-modeling ordinal regression with time invariant covariates – An application to prostate cancer data

, where

Phylogenetic trees via Hamming distance decomposition tests

N

Homogeneity tests among groups for microsatellite data

is the effective population size and

Asymptotic behavior of the scaled mutation rate estimators

\nu

Gluttonous predators: how to estimate prey size when there are too many prey

is the rate of mutation per locus per generation. Therefore,