Geographical fine-scaled distributional differentiation caused by niche differentiation in three closely related mayflies

Seasonal modifications of longitudinal distribution patterns within a stream: Interspecific interactions in the niche overlap zones of two Ephemera mayflies

“…The riverbed slope degree was calculated using a GSI map and based on the distance between points at which there was a 10‐m elevation difference (basically, 5 m mesh map information from the “Geospatial Information Authority of Japan” was used for this analysis), with the study site set as the base point. In addition, substrate coarseness was evaluated in the same manner as our previous study (Okamoto et al, 2022 ). In evaluating the canopy openness rate, five digital hemispherical photographs were taken with a camera equipped with a fisheye lens (EX‐FR200, CASIO, Tokyo, Japan) at each research site, specifically at the position of the five quadrats in which the Ephemera mayflies were collected.…”

“…japonica emerges on land boulders/cobbles and E . strigata emerges on the surface of water (Ishiwata & Takemon, 2005 ; Okamoto et al, 2022 ; Takemon, 1989 ). In order to quantitatively collect the molted emergence exuviae of E .…”

“…In fact, it is well known that environmental factors are the main factors in establishing longitudinal distribution between interspecific and intraspecific lineages, including among closely related species (e.g., aquatic insects: Hildrew & Edington, 1979 ; Ogitani et al, 2011 ; Saito & Tojo, 2016 ; Saito et al, 2018 ; freshwater snails: Atkinson et al, 2012 ; freshwater fish: Morita et al, 2016 ). Using river systems as a target of study gives an advantage of easy quantitative evaluation of various environmental factors that are closely involved in differentiating the niches of organisms inhabiting rivers such as riverbed slope gradient, flow velocity, water depth, water quality, water temperature, riverbed substrate size, the abundance of organic matter and algae periphyton, and the degree of isolation (Okamoto et al, 2022 ). Under such circumstances, detailed longitudinal distribution patterns on the microhabitat scale of freshwater animals inhabiting rivers have been frequently discussed (Costa & Melo, 2008 ; Mauchart et al, 2017 ; Morita et al, 2016 ; Ogitani et al, 2011 ; Okamoto et al, 2022 ; Roberts & Angermeier, 2007 ; Saito & Tojo, 2016 ).…”

“…Using river systems as a target of study gives an advantage of easy quantitative evaluation of various environmental factors that are closely involved in differentiating the niches of organisms inhabiting rivers such as riverbed slope gradient, flow velocity, water depth, water quality, water temperature, riverbed substrate size, the abundance of organic matter and algae periphyton, and the degree of isolation (Okamoto et al, 2022 ). Under such circumstances, detailed longitudinal distribution patterns on the microhabitat scale of freshwater animals inhabiting rivers have been frequently discussed (Costa & Melo, 2008 ; Mauchart et al, 2017 ; Morita et al, 2016 ; Ogitani et al, 2011 ; Okamoto et al, 2022 ; Roberts & Angermeier, 2007 ; Saito & Tojo, 2016 ).…”

“…As the target group in this study, we focused on an Ephemera mayfly group, whose distribution characteristics within the Japanese Archipelago have already been investigated in detail and for which the tendency for fine‐scale niche differentiation within specific river systems has been reported (Okamoto et al, 2022 ; Okamoto & Tojo, 2021 ). Regarding the longitudinal distributions of Ephemera mayflies, environmental factors have been suggested to have an essential role to play in their distribution and densities, based on the results of our own previous studies (Okamoto et al, 2022 ; Okamoto & Tojo, 2021 ). In particular, we focused on Ephemera japonica and Ephemera strigata , for which there is detailed information on reproductive seasons and emergence patterns.…”