Investigating invertebrate biodiversity around large wood: taxonomic vs functional metrics

Chiara Magliozzi,Robert C Grabowski,Anne Robertson,Albin Meyer,Philippe Usseglio-Polatera

doi:10.1007/s00027-020-00745-9

Abstract

Large wood is a key component of river channels that affects numerous hydrological, physical and geomorphological processes. It promotes a diversity of benthic habitats in-channel and has shown to support more abundant and diverse benthic macroinvertebrate assemblages in previous ecological studies. However, the effects of large wood on the structural and functional diversities of hyporheic invertebrates are less well studied, and simultaneous examination of these diversity metrics on hyporheic and benthic compartments of the stream bed has not been conducted previously. Therefore, this study investigates the taxonomic and functional diversities of hyporheic and benthic invertebrate assemblages around natural accumulations of large wood in a British lowland river. Taxonomic and functional diversities were partitioned (into alpha, beta, and gamma diversities) and examined in reaches with and without large wood (control). We found that functional diversity is often decoupled from taxonomic diversity, demonstrating a functional redundancy of the macroinvertebrate assemblage for both hyporheic and benthic zones. Moreover, the highest functional variability at alpha-scale was observed in large wood habitats, which suggests that taxonomic diversity is enhanced by the small-scale environmental heterogeneity around large wood. To this end, this study contributes empirical evidence of functional and structural responses of invertebrates to large wood accumulation. Such information could be used to better understand the ecological implications of restoration works in lowland rivers and guide more effective management strategies.

Highlights

Large wood (LW) has a profound impact on fluvial processes and ecosystems (Grabowski et al 2019)
We hypothesized that: (i) taxonomic and functional diversities would be lower in control than LW habitats because LW creates a diverse mosaic of microhabitats that enhances the diversity of available ecological niches; (ii) for both taxonomic and functional metrics, between habitats differences would be higher in LW than control habitats because LW selects for divergent types of traits and highly diverse assemblages; and (iii) gamma diversity, and the proportion of diversity explained by the variability between habitats, would be higher in LW than in control habitats because LW provides more diverse and temporally variable resources than control habitats
Taxonomic diversity of the macrofauna assemblages exhibited significant differences between river substrates (Table 2), with α-taxonomic diversity (TD) being greater in gravel for both benthic and hyporheic assemblages (Fig. 3b, c). α-functional diversity (FD) had a similar response to α-TD for the hyporheic meiofauna by habitats and river substrates (Table 2, Fig. 3a)

Summary

Introduction

Large wood (LW) has a profound impact on fluvial processes and ecosystems (Grabowski et al 2019). Large wood is delivered naturally to rivers by upland and riparian forests, through landslides and successional or disturbance pulse processes (i.e. floods, fires, windfall, erosion) from adjacent hillslopes (Boyer et al 2003). It is defined as living or dead wood in simple or complex structures, in which individual pieces are > 1 m length and > 10 cm diameter (Thevenet et al 1998; Wohl et al 2010).

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Conclusion