Aggregation pattern of individuals and the outcomes of competition within and between species: Differential equation models

The influence of spatial distribution pattern on the outcomes of intra- and interspecific competition is studied theoretically. The models developed are the generalized logistic andVolterra equations, whereLloyd 's indices of intra- and interspecies mean crowding were incorporated with their assumed linear relationship to mean density in order to express the intensity of crowding which is really effective to the existing individuals. It is shown that while the increasing patchiness of distribution has a pronounced effect of promoting the intraspecific competition and lowering the equilibrium density for individual populations, it generally relaxes the interspecific competition, making it easy for different species sharing the same niche, which would otherwise be incompatible, to coexist stably. These models thus provide a simplest theoretical basis to explain why many insect populations in nature are kept relatively rare in number and why a number of allied species often coexist freely sharing the same resource, against the “competitive exclusion principle” deduced from the originalVolterra equations.     

The effect of interspecific interaction on spatial distribution patterns in experimental populations of Cepaea nemoralis (L.) and C. hortensis (Müll.)

'Choice-chamber' population cages were used to investigate distribution patterns in mixed and unmixed populations of closely related species of landsnails, C. nemoralis (L.) and C. hortensis (Müll.). Numbers of snails migrating into cut-grass cages were affected by mixing the two species. The direction of response was not the same for both siblings. The results indicate that interspecific interaction could affect species' distribution patterns in free-living populations.     

Evolutionary games and two species population dynamics

Competition between species has long been modeled by population dynamics based on total numbers of each species. Recently, the evolution of strategy frequencies has been used successfully for competition models between individuals. In this paper, we illustrate that these two views of competition are compatible. It is shown that the rate of intra and interspecific competitions between individuals largely determines the population dynamics. Competition models over a single common resource and predator-prey models are developed from this individual competition approach. In particular, the equilibrium strategies in a co-evolving predator-prey system are shown to be more stable than the predicted strategy cycling of standard evolutionary game theory.     

Do yeasts and Drosophila interact just by chance?

The fruit fly Drosophila melanogaster and the baker's yeast Saccharomyces cerevisiae are classic research model organisms that are also associated in nature, at least around vineyards. Sharing the same ephemeral fruit niche, winged Drosophila feed on immotile yeasts. That a yeast diet is essential for larval development, and that saprophagous fruit flies are attracted to a suite of yeast volatiles, has been well established over the last century. Recently, research has focussed on the potential mutual benefit of this interaction hypothesising yeasts also benefit via dispersal from ephemeral fruits. It now appears that the concept of a co-evolved mutualism between yeasts and Drosophila has permeated the literature. However, until robust evidence regarding the evolution and maintenance of this yeast-fly association has been provided, we suggest there is no compelling evidence to reject the more simplistic null hypothesis that these interactions are due to exaptation, and not a mutualism driven by natural selection.     

Morphology and cytology of Hordeum chilense X H. bulbosum hybrids

Summary An interspecific hybrid between Hordeum chilense and H. bulbosum was produced. The hybrid resembles the male parent, but some characters from H. chilense are also present. Transgressive inheritance for other characters has also been observed. Neither chromosome instability nor homoeologous pairing was found.     

茄子和朱砂叶螨相互作用系统的研究Ⅰ.叶螨种群动态与茄子叶片丹宁酸含量变动的关系

以茄子和朱砂叶螨为对象,对叶螨种群动态与植物次生代谢物质——丹宁酸含量变动的相互关系进行了研究。发现朱砂叶螨的取食胁迫,能迅速地诱导茄子的应激反应。同时茄子以某种方式的丹宁酸含量自主调控,对叶螨种群的动态产生强烈的影响。在结合考察未受螨害植株所表现出的次生代谢准周期变动的基础上,提出了一种植物防御模式的假说。     

CLEANING BEHAVIOUR BETWEEN THE CICHLID FISH TILAPIA RENDALLI FENDALLI BOULENGER 1896 AND THE CYPRINID,LABEO CYLINDRICUS PETERS, 1852

SUMMARY

A case of interspecific cleaning behaviour is described between a cichlid host Tilapia rendalli rendalli and a Juvenile cyprinid Labeo cylindricus, in captivity. The host fish initiated the cleaning behaviour with a ‘head down’ display.     

Karyotype analysis of regenerated plants from callus cultures of interspecific hybrids of cultivated barley (Hordeum vulgare L.)

Summary The karyotype of 82 regenerated plants from callus cultures of interspecific hybrids between cultivated barley (Hordeum vulgare L.) and seven polyploid wild barley species was examined by C-banding or Feulgen staining. The karyotypic changes observed in 46 plants included aneuploidy, double haploidy, amphidiploidy, deletions, inversions, extra C-bands, and extra euchromatic segments. Apparently, chromosome 5, 6, and 7 of H. vulgare were more frequently exposed to elimination or structural change than the other chromosomes of this species. Irradiation of calli seemed to enhance the occurrence of karyotypic variants.