Higher investment in flight morphology does not trade off with fecundity estimates in a poleward range‐expanding damselfly

1. Evolutionary increases in dispersal‐related traits are frequently documented during range expansions. Investment in flight‐related traits is energetically costly and a trade‐off with fecundity may be expected during range expansion. 2. However, in contrast to wing‐dimorphic species, this trade‐off is not general in wing‐monomorphic species. In the absence of a dispersal‐‐fecundity trade‐off, an increased investment in clutch size at the expansion front is expected possibly at a cost of reduced offspring size. 3. The study evaluated investment in female flight morphology and fecundity‐related traits (clutch size, hatchling size) and potential trade‐offs among these traits in replicated populations of the poleward range‐expanding damselfly Coenagrion scitulum. 4. Females at the expansion front had a higher relative thorax length, indicating an increased investment in flight; this can be explained by spatial sorting of dispersal ability or in situ natural selection at the expansion front. Edge females produced larger hatchlings, however, this pattern was totally driven by the population‐specific thermal larval regimes and could not be attributed to the range expansion per se. By contrast, clutch sizes did not differ between core and edge populations. There was no signal of a dispersal–fecundity trade‐off either for a trade‐off between clutch size and hatchling size. 5. These results indicate that evolution of a higher dispersal ability at the expansion front of C. scitulum does not trade off with investment in fecundity, hence a dispersal–fecundity trade‐off is unlikely to slow down range expansion of this species.     

The influence of different spatial‐scale variables on caddisfly assemblages in Flemish lowland streams

1. Patterns in species assemblages are the result of the combined influence of processes acting on different spatial scales. Various studies describe the distribution of macroinvertebrate communities and their relationship with environmental factors at different geographical scales, but only a few of these studies concentrate on Western European lowlands. 2. Using Flanders as representative for the densely populated Western‐European lowlands, the specific aims of this study are: (i) to identify the different trichopteran species assemblages and to characterise them biologically using indicator species; (ii) to determine which environmental gradients most influence the observed species assemblages; and (iii) to analyse the relative importance of different spatial scale variables in constraining the Trichoptera distributions. 3. Assessment of the main environmental gradients suggested that the absence of Trichoptera from certain locations was mainly due to elevated nutrient concentrations and lower oxygen contents, confirming their sensitivity to anthropogenic disturbance. 4. Five Trichoptera species assemblages were distinguished based on Bray–Curtis dissimilarity coefficients. These assemblages did not differ significantly in species richness, but a shift in stream zonation preference was observed. In the ordination analysis 11 variables that were selected using a stepwise model building function manifested themselves as upstream–downstream and size‐related gradients. The Trichoptera assemblages in lowland streams thus appear to follow a longitudinal succession pattern that corresponds with the species‐specific preferences. 5. Partitioning the variance over the different spatial scales indicated that the reach‐scale variables were far more important in explaining the variation in species composition. The study design, which limited the minimum–maximum range of catchment‐scale characteristics, however, may have led to an overestimation of the impact of the local‐scale variables.