Investigating invertebrate biodiversity around large wood: taxonomic vs functional metrics

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.

Seasonal and spatial variation of stream macroinvertebrate taxonomic and functional diversity across three boreal regions

“…A growing body of research suggests that trait‐based approaches hold more promise in realistically assessing how changes in the environment might affect ecosystem functioning (McGill et al, 2006; Múrria et al, 2020; Verberk et al, 2013). In accordance with Magliozzi et al (2020), our study confirms that taxonomic and functional diversity are often decoupled, and that the resultant redundancy provides ecosystems with a degree of resilience to changes in environmental conditions. Despite the dependence of boreal systems on seasonal predictability (e.g., phenological synchronisations, predator prey interactions, pollination cycles, growth periods, etc.…”

Multidecadal changes in functional diversity lag behind the recovery of taxonomic diversity

“…However, after the year 2000, when both bark beetle outbreaks caused increasing nitrate levels and temperatures began noticeably rising (Baker et al, 2021), we observed declines in FRic and thus a reduction in the amount of occupied niche space. Decoupling of TD and FD is in alignment with a previous study investigating macroinvertebrate communities around natural large wood build‐ups in a British lowland river (Magliozzi et al, 2020).…”

“…However, after the year 2000, when both bark beetle outbreaks caused increasing nitrate levels and temperatures began noticeably rising(Baker et al, 2021), we observed declines in FRic and thus a reduction in the amount of occupied niche space. Decoupling of TD and FD is in alignment with a previous study investigating macroinvertebrate communities around natural large wood build-ups in a British lowland river(Magliozzi et al, 2020).The continuous decline in FEve over the observation period was driven by changes in taxonomic richness, as shown by the null model analysis (Appendix S3 Figure1b). Such decline in FEve was quantitatively similar to the decline in taxonomic evenness and is indicative of an unequal distribution of taxa (some parts of the niche space are unoccupied, while others are densely populated;Mouchet et al, 2010).…”

Implications of macroinvertebrate taxonomic resolution for freshwater assessments using functional traits: The Paute River Basin (Ecuador) case

“…Rao's quadratic diversity index (Q) (Rao, 1982) is one of the most important FD metrics (Mouchet et al, 2010) that has been widely used to measure the effects of anthropogenic activities on the FD of aquatic organisms. In general, the observed pattern is a reduction in Q values for impacted areas (Desrosiers et al, 2019;Magliozzi et al, 2020;Meng et al, 2021).…”

“…Rao's quadratic diversity index (Q) (Rao, 1982) is one of the most important FD metrics (Mouchet et al., 2010) that has been widely used to measure the effects of anthropogenic activities on the FD of aquatic organisms. In general, the observed pattern is a reduction in Q values for impacted areas (Desrosiers et al., 2019; Magliozzi et al., 2020; Meng et al., 2021). Nevertheless, Q suffers from some pitfalls (Chen et al., 2018; Liu & Rao, 1995; Pons & Petit, 1996), among which the fact that its range of values depends on the scale of the dissimilarities between the compared data sets is one of the most relevant.…”