Japanese scientists have found that common fish species may be composed of sub-populations of specialists adapted to specific narrow niches in local conditions and that these sub-populations are vulnerable to local extinction.
The study, conducted on populations of the medaka, Oryzias latipes, collected from two rivers in Nagano Prefecture (central Honshu in Japan) by Keichiro Iguchi and Satoshi Kitano, is published in the latest issue of the journal Environmental Biology of Fishes.
The authors studied the niche profiling of populations from different habitats for a factor that possibly lies behind the species being abundant within particular areas.
This was done by measuring and analysing the behavioural (particularly with regard to feeding) and morphological characteristics of each population using principal components analysis that summarised these variables into compounded elements relevant to foraging and predator avoidance.
The authors found that the medaka in the study area is actually composed of a patchwork of populations, each with their own morphological and behavioural characteristics.
The authors conclude that the medaka ...has been considered a common species not because all conspecifics behave as generalists, but because intraspecific phenotypes are rich enough to compensate for particular niches. In other word, medaka is generalized as a sum of various specialists. Such types of common species are readily threatened by the destruction of their habitat-network.
For more information, see the paper: Iguchi, K and S Kitano (2008) Local specialists among endangered populations of medaka, Oryzias latipes, harboring in fragmented patches. Environmental Biology of Fishes 81, pp. 267"276.