Factors influencing the spatial distribution patterns of the bullhead (Cottus gobio L., Teleostei Cottidae): a multi-scale study

We used general linear modelling to assess the inuence of environmental variables on the spatial distribution patterns of the bullhead (Cottus gobio) at stream system, site, and micro- habitat scales in southwestern France. Bullheads occurred at 67 sites (out of 554 sampling sites), chiey close to the source, in small and shallow streams. Population density at a site was primarily inuenced by thermal conditions. Stream width was negatively related to the probability of pres- ence of bullheads within the stream system, but positively related to local density, showing that bullhead density could increase within a range of stream width, but that wider rivers were unsuitable. Slope was negatively correlated to bullhead’s occurrence and local density, and depth was negatively correlated to local density and microhabitat use, suggesting that bullhead’s shim- ming performance was weak under greater erosive forces. Therefore, the most signicant results suggested that the distribution of populations and individuals was rst governed by the suitability of physical and hydraulic habitat, then population dynamics at a site was mainly governed by the thermal regime. Multi-scale studies of factors inuencing a species’ distribution thus allow to integrate patterns observed at dierent scales, and enhance our understanding of interactions between animals and their environment. Such models are essential in the exploratory phase of fundamental and applied investigations, because they help to target further research, and they should inuence the measures to be taken in eld surveys or conservation plans.Peer reviewe