Geology‐dependent impacts of forest conversion on stream fish diversity

Abstract

Forest conversion is one of the greatest global threats to biodiversity, and land-use change and subsequent biodiversity declines sometimes occur over a variety of underlying geologies. However, how forest conversion and underlying geology interact to alter biodiversity is underappreciated, although spatial variability in geology is considered an integral part of sustaining ecosystems. We aimed to examine the effects of forest conversion to farmland, the underlying geology, and their interaction on the stream fishes' diversity, evenness, and abundance in northeastern Japan. We disentangled complex pathways between abiotic and biotic factors with structural equation modeling. Species diversity of stream fishes was indirectly shaped by the interaction of land use and underlying geology. Diversity declined due to nutrient enrichment associated with farmlands, which was mainly the result of changes in evenness rather than by changes in species richness. This impact was strongest in streams with volcanic geology with coarse substrates probably because of the differential responses of abundant stream fishes to nutrient enrichment (i.e., dominance) and the high dependency of these fishes on large streambed materials during their life cycles. Our findings suggest that remediation of deforested or degraded forest landscapes would be more efficient if the interaction between land use and underlying geology was considered. For example, the negative impacts of farmland on evenness were larger in streams with volcanic geology than in other stream types, suggesting that riparian forest restoration along such streams would efficiently provide restoration benefits to stream fishes. Our results also suggest that land clearing around such streams should be avoided to conserve species evenness of stream fishes.

Effects of multiple stressors on recruitment of long‐lived endangered freshwater mussels

“…The stone loach ( Noemachelius barbatulus toni ), white‐spotted charr, and sticklebacks ( Pungitius spp.) are the most abundant fish species in the streams under study (Ishiyama et al, 2021). Another congeneric species, Margaritifera laevis , also occurs in the study region (Miura et al, 2019a; Miura et al, 2023).…”

Multiple stressors and recruitment failure of long-lived endangered freshwater mussels with a complex life cycle

“…Low habitat quality can reduce host fish availability and the infection success of glochidia larvae (Kawajiri et al, 2021). However, the host fish density in the study region was mainly limited by catchment size and habitat complexity and not by habitat degradation (Ishiyama et al, 2020). In addition, the relationships between glochidia load of both age classes (YOY and ≥1 + ) and fine sediment and nutrient concentrations were also unclear (GLM with log-likelihood ratio tests, YOY: P = 0.92 and P = 0.38; ≥1 + : P = 0.24, and P = 0.62).…”

“…Electrical conductivity (EC, mS/m) had a strong positive correlation with total nitrogen (TN) and total phosphorus (TP) in river surface water in the study region (r = 0.88 and 0.45, P <0.05, N = 24), suggesting that EC could be used as an indicator of nutrient concentration in the rivers (Ishiyama et al, 2020). EC was measured (WM-32EP, TOA DKK Co., Japan) at the uppermost part of each reach during monitoring of mussel gravidity, when fish sampling, and at preprint (which was not certified by peer review) is the author/funder.…”

“…The stone loach Noemachelius barbatulus toni, white-spotted char, and sticklebacks Pungitius spp. are the most dominant fish species in the studied streams (Ishiyama et al 2020).…”

The effects of endangered freshwater pearl mussels on channel morphology and flow in a low-gradient sandy river

“…In the fish community, Pungitius spp. were the most abundant, and Salvelinus leucomaenis leucomaenis (Pallas, 1814) and Gymnogobius urotaenia Hilgendorf, 1879 were among the secondarydominant fish species (Ishiyama et al, 2020). In addition, Oncorhynchous masou masou (Brevoort, 1856), Lethenteron sp., Cottus nozawae Snyder, 1911, and Platichthys stellatus (Pallas, 1788) were occasionally found.…”