Food sharing: a model of manipulation by harassment

Most analyses of food-sharing behavior invoke complex explanationssuch as indirect and delayed benefits for sharing via kin selectionand reciprocal altruism. However, food sharing can be a moregeneral phenomenon accounted for by more parsimonious, mutualisticexplanations. We propose a game theoretical model of a generalsharing situation in which food owners share because it is in their own self-interest—they avoid high costs associatedwith beggar harassment. When beggars harass, owners may benefitfrom sharing part of the food if their consumption rate islow relative to the rate of cost accrual. Our model predictsthat harassment can be a profitable strategy for beggars if they reap some direct benefits from harassing other than sharedfood (such as picking up scraps). Therefore, beggars may manipulatethe owner's fitness payoffs in such a way as to make sharingmutualistic.     

Conformist learning in nine-spined sticklebacks' foraging decisions

Theoretical analyses have reported that in most circumstances where natural selection favours reliance on social learning, conformity (positive frequency-dependent social learning) is also favoured. These findings suggest that much animal social learning should involve a copy-the-majority strategy, yet there is currently surprisingly little evidence for conformist learning among animals. Here, we investigate this possibility in the nine-spined stickleback (Pungitius pungitius) by manipulating the number of demonstrator fish at two feeders, one rich and one poor, during a demonstration phase and evaluating how this affects the likelihood that the focal fish copy the demonstrators'' apparent choices. As predicted, we observed a significantly increased level of copying with increasing numbers of demonstrators at the richer of the two feeders, with copying increasing disproportionately, rather than linearly, with the proportion of demonstrators at the rich foraging patch. Control conditions with non-feeding demonstrators showed that this was not simply the result of a preference for shoaling with larger groups, implying that nine-spined sticklebacks copy in a conformist manner.     

Patterns of metric variability in the dentition of Papio ursinus

The present investigation assesses a number of explanations for the patterns of variability in dental dimensions. Coefficients of variation were calculated for mesiodistal and buccolingual diameters in a sample of 105 Papio ursinus crania (52 male, 53 female). Variability profiles consisting of arrays of values of coefficients of variation were evaluated by means of Friedman's two-way analysis of variance and Kendall's coefficient of concordance. Although molar teeth were found to be the most dimensionally stable, our results failed to support either the morphogenetic field theory or the occlusal complexity hypothesis. The data presented here are generally supportive of Pengilly's phenotypic complexity theory. However, speciesspecific clustering patterns found in our regressions of dimensional variability on mean tooth size suggest that differences in variability levels might be related to differences in selective pressures.     

Natural selection. V. How to read the fundamental equations of evolutionary change in terms of information theory

The equations of evolutionary change by natural selection are commonly expressed in statistical terms. Fisher's fundamental theorem emphasizes the variance in fitness. Quantitative genetics expresses selection with covariances and regressions. Population genetic equations depend on genetic variances. How can we read those statistical expressions with respect to the meaning of natural selection? One possibility is to relate the statistical expressions to the amount of information that populations accumulate by selection. However, the connection between selection and information theory has never been compelling. Here, I show the correct relations between statistical expressions for selection and information theory expressions for selection. Those relations link selection to the fundamental concepts of entropy and information in the theories of physics, statistics and communication. We can now read the equations of selection in terms of their natural meaning. Selection causes populations to accumulate information about the environment.     

Global patterns in the shape of species geographical ranges reveal range determinants

Aim Do species range shapes follow general patterns? If so, what mechanisms underlie those patterns? We show for 11,582 species from a variety of taxa across the world that most species have similar latitudinal and longitudinal ranges. We then seek to disentangle the roles of climate, extrinsic dispersal limitation (e.g. barriers) and intrinsic dispersal limitation (reflecting a species’ ability to disperse) as constraints of species range shape. We also assess the relationship between range size and shape. Location Global. Methods Range shape patterns were measured as the slope of the regression of latitudinal species ranges against longitudinal ranges for each taxon and continent, and as the coefficient of determination measuring the degree of scattering of species ranges from the 1:1 line (i.e. latitudinal range = longitudinal range). Two major competing hypotheses explaining species distributions (i.e. dispersal or climatic determinism) were explored. To this end, we compared the observed slopes and coefficients of determination with those predicted by a climatic null model that estimates the potential range shapes in the absence of dispersal limitation. The predictions compared were that species distribution shapes are determined purely by (1) intrinsic dispersal limitation, (2) extrinsic dispersal limitations such as topographic barriers, and (3) climate. Results  Using this methodology, we show for a wide variety of taxa across the globe that species generally have very similar latitudinal and longitudinal ranges. However, neither neutral models assuming random but spatially constrained dispersal, nor models assuming climatic control of species distributions describe range shapes adequately. The empirical relationship between the latitudinal and longitudinal ranges of species falls between the predictions of these competing models. Main conclusions We propose that this pattern arises from the combined effect of macroclimate and intrinsic dispersal limitation, the latter being the major determinant among restricted‐range species. Hence, accurately projecting the impact of climate change onto species ranges will require a solid understanding of how climate and dispersal jointly control species ranges.     

On the electron delocalization in cyclopropenylidenes - An experimental charge-density approach

The extent and nature of cyclic electron delocalization in free and coordinated cyclopropenylidene carbenes has been analyzed by combined experimental and theoretical charge-density studies. The significant asymmetry of the C-C bond lengths in substituted cyclopropenylidene carbenes was identified as cooperative effect which depends on contributions of both σ- and π-bonding. We show that analyses of (i) the topology of the Laplacian of the electron density distribution and (ii) the out-of-plane atomic quadrupole moments - the charge-density analogues of p_π occupation - allow to distinguish between the influence of σ- and π-electrons on cyclic electron delocalization. These studies hint for pronounced electron localization in the carbene lone pair region which dominates the electronic structure of free cyclopropenylidene carbenes and hinders the establishment of true aromaticity. We further investigated the electron donating/withdrawing ability of cyclopropenylidene ligands relative to N-heterocyclic carbenes. The experimental benchmark systems LCr(CO)₅ (L = 2,3-diphenylcyclopropenylidene and 1,2-dimethylimidazol-2-ylidene) show that the cyclopropenylidene ligand clearly displays the higher π-acceptor capability relative to N-heterocyclic carbenes.