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Increasing evidence for insect biodiversity decline requires an identification of the causes but also an improved understanding of the limitations of the various underlying sampling methods. Trap comparisons foster comparability of larger-scale biodiversity studies by providing a deeper understanding of the variations in species abundances and trait compositions due to variations in trap characteristics. In our study, we compared five Malaise trap types on their catchability of butterfly species and noctuid moths and examined for the butterflies how this can be related to traits. We showed marked differences in species and trait occurrence in the samples of the different trap types which seemed to be influenced by roof colour (white, black) and trap shape (Townes trap: high, wide roof, Bartak trap: low, narrow roof). We found most butterfly species and most butterfly biomass in the white-roofed Townes trap. All butterfly traits were represented with most individuals in this trap. Compared with its black counterpart, it showed increased catches for pale butterflies and forest species. We found that dark-roofed traps captured fewer butterfly species and had a lower butterfly biomass. Townes traps captured more butterflies with larger wingspans, egg-laying locations higher above ground, and tree feeding behaviour compared to Bartak traps. Depending on the season and habitat, the differences in species capture may affect overall insect biomass.
Hydrological variability is a key factor in structuring biotic and abiotic processes in river ecosystems and is of particular importance to fish populations. We used 171 hydrological indices (HI) and young-of-the-year (YOY) fish abundances as indicators of reproductive success to compare species' response patterns to high and low flows on short-, intermediate-, and long-term scales. Our study included 13 common fish species in headwater streams of North Rhine-Westphalia, Germany. Generalized linear models using YOY abundances and HI on high- and low-flow patterns explained on average 64 % of the variability. HI calculated from long time series worked better than HI describing short- and intermediate-term high- and low flows. Species' reproductive success response to low flow HI depended on specific ecological traits whereas high flow HI differentially affected species according to their life history strategies. Equilibrium strategists responded negatively to high frequency and magnitude along with late timing of high flow, while periodic and opportunistic species mostly thrived under these conditions. We identified four species traits that mediated these differences between life history strategies. The reproductive success of species with low relative fecundity, large eggs and larvae, and long incubation periods was negatively impacted by the high frequency, high magnitude, and late timing of high flows. Conversely, the reproductive success of species with high relative fecundity, short incubation periods and small eggs and larvae was fostered by strong, frequent, and late high flows. The consideration of the relationship between reproductive success, life history, and fish species traits over several years under a range of flows is a novel step towards the implementation of measures to mitigate negative impacts and enhance conditions for successful fish reproduction.
Understanding stream fish habitat use in response to hydrological variability is key for effective riverine management under increasing climate-induced flow extremes. In this field study, we investigated microhabitat use by brown trout (Salmo trutta Linnaeus, 1758) in a Central European low mountain stream using PIT telemetry over three years. Continuous monitoring captured habitat preferences under low, moderate, and high-flow conditions. During low flows, trout mainly used riffles with stable, coarse substrates, while juveniles occupied more cryptic refuges. At moderate discharge, detection rates across age groups converged, suggesting more uniform habitat use, possibly due to greater accessibility or reduced spatial constraints. Under high-flow conditions, trout retreated to deeper pools offering structural cover such as woody debris and undercut banks, likely reducing energy expenditure and predation risk. Juvenile detections were particularly scarce when discharge reached the uppermost high-flow range, possibly reflecting displacement, reduced swimming capacity, or use of refuges beyond detection range. Our findings highlight the need to preserve a mosaic of habitat types, including riffles, pools and complex cover, to support age-specific responses and enhance trout resilience under hydrological extremes. This study underscores the value of long-term in situ data for informing conservation strategies in dynamic freshwater ecosystems.
