Multiple factors and thresholds explaining fish species distributions in lowland streams

Abstract

a b s t r a c tAppropriate restoration and conservation measures require a good understanding of the factors limiting the distribution of species, the presence of steep changes in the distribution along environmental gradients and the effect of environmental interactions on species distribution. We used 12 environmental variables describing connectivity, hydrology, climate and stream morphology, to model the distributions of 17 fish species from 2005 Swedish stream sites that were sampled between 2000 and 2011. Modeling was performed using boosted regression trees and random forest, two machine learning techniques to assess the relationship between species distributions and their environment. Temperature, width and connectivity (minimum distance to lake or the sea and water discharge), were the most important variables explaining changes in species distribution at large spatial scales. Response curves of fitted occurrence probabilities along predictors often showed abrupt changes, however, clear threshold effects were difficult to detect. Our results show also differences across species and even in the outcomes of the two algorithms, implying that a simultaneous assessment of multiple species may provide a better signal of ecosystem change than the use of surrogate species.

Nature‐like fishways as compensatory lotic habitats

“…The fish fauna in each bypass was compared with the closest lotic habitat in the same stream where data was available, irrespective if the natural site was situated upstream or downstream of the bypass, potentially creating some unexpected dependency in some cases compared to other. However, as bypasses are efficient for most species and ages of fish (Calles & Greenberg, ; Noonan et al, ) and the studied fish species in this report are common in rivers in lowland Sweden (Degerman & Sers, ; Trigal & Degerman, ), the efficiency of the individual bypass as a migration route was not considered in the study. Comparisons between habitat types were done with the closest natural site within the same stream to assure that large‐scale environmental conditions (e.g., climate and distance to sea) and more local‐scale factors (e.g., nutrient status and land use) were comparable.…”

“…P. fluviatilis was significantly more abundant in the fishway habitats, perhaps surprising as P. fluviatilis is considered a predominantly lentic species (Degerman & Sers, ; Trigal & Degerman, ). Generally, P. fluviatilis shows increasing occurrence in river stretches with increasing proximity to lentic habitats (op.…”

Coastal river connectivity and the distribution of ascending juvenile European eel (Anguilla anguilla L.): Implications for conservation strategies regarding fish‐passage solutions

“…Water temperature influences the composition of riverine species and their respective catchability using electrofishing by wading, as, for instance, diel or seasonal swimming activity and migration patterns are affected by temperature (e.g. Trigal & Degerman, ). Moreover, for eels, temperature has been shown to be an important correlate for initiation of elver and juvenile migration (White & Knights, ), and has a large impact on swimming and climbing activity and behaviour (Linton, Jónsson, & Noakes, ).…”

Pike Esox Lucius Distribution and Feeding Comparisons in Natural and Historically Channelized River Sections

“…The analysis of the spread of pike depending on the type of river stage showed that, there is a higher density of pike 1.4 pike/(100 m 2 ) in channelized river habitats; where as in natural river sections they are on average 0.9 pike/(100 m ____________________________________________________________________________ 2016 / 18 37 species distribution factors affecting rivers was discovered that, the most important factors influencing the spread of pike is the substrate, the barriers and the water temperature, as well as the width of the river [3].…”

“…Such activities homogenize the hydraulic and geomorphological characteristics of streams. This results in a decrease in the amount of species, their incidence and prevalence in certain areas, which ultimately negatively affects the function of the ecosystem [2], [3]. One of the best examples of Latvia in this context are the Daugava River.…”