Complex ecological models with simple dynamics: From individuals to populations

The aim of this work is to study complex ecological models exhibiting simple dynamics. We consider large scale systems which can be decomposed into weakly coupled subsystems. Perturbation Theory is used in order to get a reduced set of differential equations governing slow time varying global variables. As examples, we study the influence of the individual behaviour of animals in competition and predator-prey models. The animals are assumed to do many activities all day long such as searching for food of different types. The degree of competition as well as the predation pressure are dependent upon these activities. Preys are more vulnerable when doing some activities during which they are very exposed to predators attacks rather than for others during which they are hidden. We study the effect of a change in the average individual behaviour of the animals on interspecific relationships. Computer simulations of the whole sets of equations are compared to simulations of the reduced sets of equations.     

Assessment of five cultivars of potato (Solatium tuberosum L.) in a competition diallel

In 1992 and 1993, potato cultivars Cara, Estima, Pentland Dell, Pentland Javelin and Torridon were assessed in all possible pairings in three consecutive drills, such that one member of the pair (the cultivar) was the centre-drill, and the other member (the neighbour) was in the two adjacent drills. Each year the trial was a randomised complete block design with four replicates. Inter-cultivar competition was present for height, total tuber yield, ware yield and dry matter content, but not for emergence and maturity. Cultivar heights and dry matter contents under inter-cultivar competition and in pure-stands were highly correlated, whereas for total and ware yields, the rankings of cultivars in pure-stands were different from those under competition. Pure-stand yields were predicted for the two years separately because of year × cultivar and year × neighbour interactions. When the average total yield of the outer-drills was used as a covariate to adjust centre-drill yields to pure-stands, predicted yields were closer to those observed than were yields under competition, but there was little improvement in the correlations. In contrast, not only were the predicted values even closer to the observed ones when based on individual neighbour effects, the correlations were much higher (r = 0.76–0.94). Unfortunately, in plant breeding trials with large numbers of entries, precise estimation of individual neighbour effects would require an unrealistically large number of replicates. Hence, for the final stages of yield assessment of new cultivars, it is still desirable to use multiple-drill plots and to discard the outside drills where inter-cultivar competition can occur.     

Metabolic interactions between anaerobic bacteria in methanogenic environments

In methanogenic environments organic matter is degraded by associations of fermenting, acetogenic and methanogenic bacteria. Hydrogen and formate consumption, and to some extent also acetate consumption, by methanogens affects the metabolism of the other bacteria. Product formation of fermenting bacteria is shifted to more oxidized products, while acetogenic bacteria are only able to metabolize compounds when methanogens consume hydrogen and formate efficiently. These types of metabolic interaction between anaerobic bacteria is due to the fact that the oxidation of NADH and FADH₂ coupled to proton or bicarbonate reduction is thermodynamically only feasible at low hydrogen and formate concentrations. Syntrophic relationships which depend on interspecies hydrogen or formate transfer were described for the degradation of e.g. fatty acids, amino acids and aromatic compounds.     

Fluorescence correlation spectroscopy with high count rate and low background: analysis of translational diffusion

An epi-illuminated microscope configuration for use in fluorescence correlation spectroscopy in bulk solutions has been analyzed. For determining the effective sample dimensions the spatial distribution of the molecule detection efficiency has been computed and conditions for achieving quasi-cylindrical sample shape have been derived. Model experiments on translational diffusion of rhodamine 6G have been carried out using strong focusing of the laser beam, small pinhole size and an avalanche photodiode in single photon counting mode as the detector. A considerable decrease in background light intensity and measurement time has been observed. The background light is 40 times weaker than the fluorescence signal from one molecule of Rh6G, and the correlation function with signal-to-noise ratio of 150 can be collected in 1 second. The effect of the shape of the sample volume on the autocorrelation function has been discussed. Correspondence to: R. Rigler     

Extra-weak chemiluminescence of drugs XV. Method for determining stability of Toki-shakuyaku-san extract granules

The purpose of the study was to evaluate the quality of Toki-shakuyaku-san extract granules (TJ-23) using chemiluminescence (CL). A linear relationship was obtained between the log value of the CL of TJ-23 and the reaction temperature. An excellent correlation (r= 0.999) was found between the slope of this curve (ΔA) and the colour intensity due to the browning reaction occurring at the early stage of the Maillard reaction.     

Inter-plot competition in yield trials of potatoes (Solanum tuberosum L.) with single-drill plots

An experiment was carried out to assess the significance of inter-plot competition in a yield trial of potato cultivars. Seventeen cultivars were deliberately chosen and assessed for yield in single-drill and four-drill plots. Inter-plot competition for fresh-weight yield was a significant factor in the single-drill plots. It was modelled using a common competition coefficient with a covariate based on neighbour fresh-weight yields. In contrast, there was no statistically significant inter-plot competition for specific gravity. After adjustment for inter-plot competition, varietal ranking in estimated monoculture yield differed little from that based on unadjusted means. However, there was a reduction in the range of yield estimates, and a closer agreement with the observed pure-stand yields from the inner two drills of the four-drill plots. The adjustment for monoculture performance was most pronounced for the higher and lower yielding varieties, as expected from the assumption that the performance of high yielding varieties was enhanced in a competitive environment at the expense of low yielding ones. A general and flexible method of estimating competition coefficients in variety trials, together with a suitable algorithm, was developed and is explained in an appendix. It was used to check for inter-plot competition in a number of potato trials with single-drill plots and a large number of entries. Competition was found in some trials but not in others. Thus, where potato tubers are grown in single-drill plots for assessment of fresh-weight yield, adjustment should be made for inter-plot competition when evidence of inter-drill competition is found.     

QUANTITATIVE GENETICS OF RESPONSE TO COMPETITORS IN NEMOPHILA MENZIESII: A GREENHOUSE STUDY

To determine the potential for adaptation to a local biotic environment, we examined the magnitude and nature of genetic variation in response to neighboring plants within a natural population of the native California annual, Nemophila menziesii. A total of 22 plants from a natural population were crossed in three reciprocal factorials. The progeny were grown in a greenhouse in nine treatments that varied in conspecific density and in the density of a naturally co-occurring grass species, Bromus diandrus. Increasing the density of each species significantly reduced individual survival, fruit number, and dry weight. Among survivors, we found small to moderate heritability of dry weight within treatments. Additive genetic correlations (r_A) of dry weight between competitive regimes were generally large and positive. In no case were they significantly different from 1, as expected under the null hypothesis that the relative performance of the genotypes under consideration is the same in all environments. On the basis of these results, we cannot conclude that the structure of genetic covariation within this population would promote genetic differentiation in response to locally varying conditions of density of these two species. Aspects of the experiment that may have compromised our ability to detect r_A differing from 1 are discussed.     

Social group composition modulates the role of last male sperm precedence in post-copulatory sexual selection

In many species, the order in which males mate with a female explains much of the variation in paternity arising from post-copulatory sexual selection. Research in Drosophila suggests that mating order may account for the majority of the variance in male reproductive success. However, the effects of mating order on paternity bias might not be static but could potentially vary with social or environmental factors. To test this idea, we used an existing dataset, collated from an experiment we previously published (Morimoto et al., PLoS One, 11, 2016, e0154468), with the addition of unpublished data from the same experiment. These previous experiments manipulated larval density in Drosophila melanogaster which generated variation in male and female body size, assembled groups of individuals of different sizes, and measured the mating success and paternity share of focal males. The data presented here provides information on each focal male's mating order and the frequency in which focal males remated with same females (‘repetitive matings’). We combined this information with our previously reported focal male reproductive success to partition variance in paternity into male mating order and repetitive matings across groups that differed in the body size composition of males and females. We found, as expected, that male mating order explained a considerable portion of the variance in male paternity. However, we also found that the impact of male mating order on male paternity was influenced by the body size composition of groups. Specifically, males that tended to mate last had a greater paternity advantage, and displayed lower variance, in groups containing a heterogenous mixture male body sizes than in groups with a single male body size. Repetitive mating only had a minor contribution to the variance in male paternity share across all experiments. Overall, our findings contribute to the growing body of research showing that post-copulatory sexual selection is subject to socio-ecological influences.     

Maximal ecological diversity exceeds evolutionary diversity in model ecosystems

Understanding community saturation is fundamental to ecological theory. While investigations of the diversity of evolutionary stable states (ESSs) are widespread, the diversity of communities that have yet to reach an evolutionary endpoint is poorly understood. We use Lotka–Volterra dynamics and trait-based competition to compare the diversity of randomly assembled communities to the diversity of the ESS. We show that, with a large enough founding diversity (whether assembled at once or through sequential invasions), the number of long-time surviving species exceeds that of the ESS. However, the excessive founding diversity required to assemble a saturated community increases rapidly with the dimension of phenotype space. Additionally, traits present in communities resulting from random assembly are more clustered in phenotype space compared to random, although still markedly less ordered than the ESS. By combining theories of random assembly and ESSs we bring a new viewpoint to both the saturation and random assembly literature.