Shifts in mollusc traits following floodplain reconnection: Testing the response of functional diversity components

Andrea Rumm,Michael Gerisch,Frank Dziock,Mathias Scholz,Francis Foeckler,Rebecca M B Harris,Christiane Ilg

doi:10.1111/fwb.13082

Abstract

Abstract Restoration of ecosystems can mitigate the global loss of biodiversity and provide essential ecological functions and services. Although trait composition and functional diversity (FD) are important tools in assessing recovery processes, very few restoration projects use them to evaluate restoration success. Consequently, little is known about trait and FD trajectories following restoration measures. Here, we tested the effect of dyke‐slotting to reconnect a floodplain on the trait response of mollusc communities over 6 years, based on a random stratified sampling design (plots within areas) with before and after control impact. Trait characteristics included flood resistance, drought resistance and resilience from which community‐weighted mean trait values were derived. FD and its components (alpha, beta, gamma) were calculated with Rao's quadratic entropy. Flood duration in the restored area increased from 4–13 to 6–17 weeks/year after reconnection, similarly to the reference area (4–10 to 6–14 weeks). Hence, the re‐connection by dyke‐slotting had no substantial effect on flood duration (due to seepage water). Despite that, dyke‐slotting triggered weak but significant shifts in the trait compositions of the restored floodplain mollusc communities. Traits reflecting species’ resilience, crushing resistance and drought resistance increased in abundance, while traits characteristically found in more stable habitats decreased (e.g. cross‐fertilisation, diet specialisation). Overall, trait composition of the restored area progressively moved to that found in the active floodplain. While there were some significant temporal changes in FD within areas (reference, restored), there were no significant effects of dyke‐slotting on any of the FD indices. The incorporation of spatiotemporal dynamics of FD and trait composition may facilitate the evaluation of restoration trajectories, especially when different components (hierarchical FD configuration, single trait distributions) are considered together. Such complementary approaches could be integrated in future restoration monitoring programs.

Highlights

The restoration of ecosystems can mitigate the global loss of biodiversity (Bullock, Aronson, Newton, Pywell, & Rey-Benayas, 2011)
Trait composition of the restored area progressively moved to that found in the active floodplain
The incorporation of spatiotemporal dynamics of functional diversity (FD) and trait composition may facilitate the evaluation of restoration trajectories, especially when different components are considered together

Summary

| INTRODUCTION

The restoration of ecosystems can mitigate the global loss of biodiversity (Bullock, Aronson, Newton, Pywell, & Rey-Benayas, 2011). Gallardo, Gascon, Garcıa, & Comın, 2009; Lamouroux, Gore, Lepori, & Statzner, 2015; and studies therein; Reckendorfer, Baranyi, Funk, & Schiemer, 2006), knowledge about the actual success of semi-terrestrial floodplain restoration measures is scarce, especially in terms of the functional effects on the plant and animal communities in those intermittent habitats (Espan~ol et al, 2015). It remains to be tested whether floodplain reconnection sustainably recovers communities with trait compositions typical for floodplain ecosystems. We expected FD turnover between mollusc communities (i.e. beta FD) to decrease

| METHODS

| RESULTS

| DISCUSSION

Findings

| CONCLUSIONS