General community structure
The understanding of what determines the distribution of species abundances in a community plays a central role in ecology, and considerable controversy and uncertainty remain in this endeavour. It is likely that numerous factors affect the shape of this distribution. One possibility to reduce the complexity of this problem is to look not at the abundances for the whole community, but for pairs of ecologically similar species. Using a dataset of 151 breeding birds communities stratified in five forest types, we built the frequency distributions of the proportional abundances for pairs of similar species for each type of forest. The observed distributions are statistically different from distributions for pairs of ecologically distant species, a result incompatible with neutral theories of species abundances. We investigated this outcome within the frame of niche theory. We confronted the observed distributions with theoretical models of niche splitting. We found a tight agreement with a model involving the splitting of two independent factors, with one competitor tending to be more efficient with both factors. This approach has the potential to shed new light on the mechanisms affecting abundances in a community context.
We intend to understand life as a `complex system', by unveiling universal features underlying all biological systems. For this purpose, we take a constructive approach, by setting up a simple system both experimentally and theoretically, and answer general questions on a biological system.
First, I discuss universal statistical laws of chemical abundances in a cell that sustains recursive production. From theoretical studies of simple protocell models, discovered are a power law law in average gene expression and log-normal distribution of the abundances of each chemical over cells. Experimental verification of these laws is also presented.
Next, if time is allowed, I discuss relevance of these phenotypic fluctuations to evolution, by generalizing fluctuation-dissipation theorem in physics, to obtain relationship between phenotypic fluctuations and genetic evolution. The proposed relationship is confirmed both in experiments and in model simulations. General relationship between phenotypic fluctuation and genetic variance is also derived from the evolutionary stability hypothesis.