[MIS24-05] Formation of distribution pattern of Ephemera mayflies by altitudinal gradient: Analyses of its process and factors
Keywords:Altitudinal gradient, Distribution pattern, Aquatic insect
The Japanese Archipelago is consisted many islands that is dominated by mountain areas. In mountainous areas, various environments change drastically depending on the altitude, e.g. temperature, soil quality, geographical features, and vegetation types. Changes in the environments associated with altitudinal gradients also have some significant effects on stream environments. For example, it is known well that fish and aquatic insects have different fauna depending on sites within stream (i.e. between upstream and downstream regions of streams). In particular, with respect to aquatic insects, even between closely related species each other, the tendency for species to be replaced between upstream and downstream environments, has been strongly recognized. Such distribution tendency has also been suggested for the three species of genus Ephemera we are interested in. Generally, from upstream to downstream, it feels that the three Ephemera species: E. japonica, E. strigata and E. orientalis, inhabiting in this order. However, how such a distribution pattern is formed is not yet well understood. Under such circumstances, we have begun to investigate the process of forming such a distribution pattern and the factors that determine it. We used the “Mega-data” (i.e. National Census on River Environments including the dam and reservoir edition, habitat data acquired by ourselves, and others) on the distribution of these Ephemera mayflies to statistically narrow down the preferences of each of the three species. And, we comprehensively analyzed these habitat information, GIS and data of many environmental factors. As the results of these analyses, it became clear that environmental factors closely related to the altitudinal gradient were strongly related to the distribution patterns of three Ephemera mayflies. In addition, we simulated how these three Ephemera mayflies' distribution areas have been changed due to Quaternary climate change cycles, using the software MAXENT. Although it was revealed that there are niche differentiations within the three Ephemera mayflies our focused, there are overlaps in their respective preferred niche width. Furthermore, it was newly revealed that any inter-special interaction occurring in the areas where inter-special niches overlap. Therefore, it is considered that the distribution pattern of three Ephemera mayflies according to the altitudinal gradient is formed as an overall result such as mild niche differentiation and also gentle inter-special competition.