Drivers of aquatic macroinvertebrate richness in spring fens in relation to habitat specialization and dispersal mode

Abstract

Aims The aim was to identify the main drivers of aquatic macroinvertebrate species richness in spring‐fen habitats (i.e. groundwater seepage wetlands) because these habitats are among the most threatened temperate biodiversity hotspots. Location Isolated spring fens in the western Carpathian Mountains. Methods Assemblages of Tricladida, Clitellata, Mollusca, Ephemeroptera, Plecoptera, Trichoptera and Diptera were sampled at 48 fens distributed evenly along a gradient of water mineral richness and grouped according to habitat specialization and dispersal mode. Several physicochemical parameters that have been reported to be the main drivers of species distribution were recorded for each site, along with radiocarbon measurements of the absolute age of the sites. The numbers of species in the taxonomic groups analysed were modelled as a function of the predictors via multiple linear regressions. Results We achieved a notably higher sampling efficiency than had been used in previous spring aquatic macroinvertebrate studies. In total, we collected and identified 255 species within 331 taxa from > 235,000 individuals. The number of species in all taxonomic groups increased with water discharge but the highest predictive power was obtained with water redox potential, which explained as much as 55.7% of the specialist species richness variance. We found contrasting and systematic differences in the importance of predictors related mainly to the level of species habitat specialization. Species richness of spring‐fen specialists was strongly determined by the main environmental gradient of change in groundwater chemistry, while generalists primarily reflected habitat stability linked to higher water discharge, habitat size and absolute age. Main conclusion Isolated island‐like spring fens can harbour unusually species‐rich assemblages of aquatic macroinvertebrates, the species richness of which is shaped by contrasting mechanisms dependent mainly on habitat specialization and also partly on dispersal mode. The richness of habitat specialist species seen at calcareous fens indicates their conservation priority.

The harpacticoid assemblages (Copepoda: Harpacticoida) in the Western Carpathian spring fens in relation to environmental variables and habitat age

“…In the Western Carpathian spring fens, habitat age is often positively linked to habitat size and discharge (Horsák et al, , 2015 Table 3), which is the consequence of larger spring fens with bigger water volume having a higher probability to endure Holocene climatic changes (Hájek et al, 2011b). In this study, species density and total abundance were weakly correlated with size and discharge too (R S : 0.36-0.38; Table 4).…”

“…Further, rather than colonization driven processes and age effect, which were found to influence spring fen assemblages of some other passive dispersers (Hájek et al, 2011a;Horsák et al, 2012Horsák et al, , 2015, the harpacticoid species richness may reflect habitat complexity. Further research should concentrate especially on disentangling the role of habitat heterogeneity and species small-scale distribution for ␣-diversity in the spring fens.…”

“…Moreover, larger spring fens may have on average more stable conditions than smaller ones and due to stronger upwelling they may be less susceptible to temperature fluctuations. Larger sites may thus harbour long established and abundant populations (Horsák et al, 2015) and more species may live there thanks to high habitat heterogeneity. Zhai et al (2015) found out that ostracod assemblages in the West Carpathian spring fens showed a significant spatial structure probably due to dispersal limitations.…”

“…Poulíčková et al, 2005;Hájková et al, 2012;Horsák et al, 2015). In the spring fens, whose age spans from Late Glacial to modern times, a positive relationship between number of species and habitat age was found for habitat specialists with bad dispersal abilities .…”

Factors explaining community contrast of Trichoptera assemblages at insular Western Carpathian spring fens to the adjacent headwaters

“…The area of the fen and its shortest distance to the neighbouring stream was measured in situ or by using orthophoto maps at larger sites. The absolute age of each fen was determined based on radiocarbon dates taken from organic material isolated in the bottom approximately three‐centimeter thick layer of the peaty sediment, taken at a point within the site with the thickest peat accumulation; details are available in Horsák et al ().…”