The importance of the biodiversity is one of the general concerns for both scientists and non-scientists. Species diversity, such as number of species and/or phylogenic diversity, are suggested to increase ecosystem functioning and to enhance the stability of communities. However, the ecological functions and significances of diversity within a group, including genetic diversity in a population and personalities in a society, have not been elucidated. A general framework on the relationship between diversity within a group and its functions are largely lacking. 
 I have demonstrated the ecological function and its condition dependence in a couple of insects exhibiting genetically-determined phenotypic diversity in a population. In the fruit fly, Drosophila melanogaster, I revealed that behavioural diversity increases short-term population productivity only under low nutrient condition, where rare morphs have fitness advantage. 
 Here I am planning to quantify the effects of behavioral diversity on inter-individual interactions within a population and on long-term persistence (stability) of population under various nutrient conditions. Moreover, the generality of ecological functions of phenotypic diversity within a species (population) will be tested statistic analysis and machine learning using ecological big-data. The combination of top-down and bottom-up approaches will find general framework for the function of diversity within a group.

Recently, the value of biodiversity has become widely recognized. However, little is known about the effects of intraspecific diversity and personality on the populations to which they belong (i.e., the function of genetic diversity). The purpose of this study was to quantify the effect of genetic diversity on inter-individual interaction and population dynamics (Productivity and stability) by using behavioral polymorphisms in Drosophila melanogaster. Furthermore, using ecological big data of various species of birds, we examined the relationship between intraspecific diversity and ecological performance of species.
There are two behavioral types in Drosophila melanogaster. In this species, it is known that populations with diversity have higher growth rate (or productivity) than populations without diversity. Observations of interactions between individuals showed that interindividual interactions, which prevent food intake, decreased in populations with behavioral diversity. In other words, by avoiding costly interaction, behavioral diversity is suggested to increase the efficiency of resource utilization, and thus increase the growth rate of a population. Then, by using big data on the distribution and ecological traits of birds (including size, generation time, food habit, the presence of phenotypic diversity), we analyzed the effect of intraspecific color diversity on species prosperity, and found that species exhibiting intraspecific color diversity have wider the species range and lower extinction risk, suggests that intraspecific diversity contributes to species prosperity as well as population growth and stability. Taken together, our study clarified the mechanism by which intraspecific diversity leads to an increase in population growth rate, and verified the existence of rippled effects of intraspecific diversity at the global level.