The role of habitat disturbance on biodiversity is central as it promotes changes in ecological systems. That said, still little is known about the functional consequences of such changes. Functional diversity can be used to revealing more mechanistically the disturbance effects on communities by considering the richness and the distribution of traits among the species. Here we analyzed the response of functional and species diversity of ground beetles to flood disturbance to better understand the functioning of alluvial invertebrate communities.Ground beetles were sampled in periodically flooded grasslands along the Elbe River in Germany. We used generalized linear mixed effects models to unveil the relationships between flood disturbance, species and functional diversity, respectively. We measured different components of functional diversity (functional richness, evenness, dispersion, and divergence) and analyzed species diversity by means of rarefied species richness, abundances, evenness and Simpson's diversity.We found contrasting relationships in that most species diversity measures peaked at highest disturbance levels, while most functional diversity measures decreased with increasing disturbance intensities.Inversed relationships between species and functional diversity are rarely observed, as most studies report on positive correlations. We explain increasing species diversity with a higher amount of resources available in highly disturbed sites. Decreasing functional diversity is best explained through the convergence of species traits by flood disturbance and uneven resource exploitation in highly disturbed plots (low functional evenness), suggesting strong impacts from functionally different generalist species in floodchannels. We show that the amount of resources available, and how these resources are exploited, play major roles in the functioning of floodplain ground beetle communities.
Highlights 31 diversity in eleven organism groups across five aquatic ecosystems was quantified 32 land use alone explained little variation in aquatic biodiversity 33 geo-climatic (natural) descriptors explained significantly more variation 34 and groundwater. In addition, nine geo-climatic descriptors (e.g. latitude, longitude, 48 precipitation) were used to disentangle land use effects from those of natural drivers of 49 biodiversity. Using a variance partitioning scheme based on boosted regression trees and 50 generalised linear regression modelling, we sought: i) to partition the unique, shared and 51 unexplained variation in the metrics explained by both groups of descriptor variables, ii) to 52 quantify the contribution of each descriptor variable to biodiversity variation in the most 53 parsimonious regression model and iii) to identify interactions of land use and natural 54 descriptors. The variation in biodiversity uniquely described by land use was consistently low 55 across both ecosystem types and organism groups. In contrast, geo-climatic descriptors 56 uniquely, and jointly with land use, explained significantly more variance in all 39 57 biodiversity metrics tested. Regression models revealed significant interactions between geo-58 climatic descriptors and land use for a third of the models, with interactions accounting for up 59 to 17% of the model's deviance. However, no consistent patterns were observed related to the 60 type of biodiversity metric and organism group considered. Subdividing data according to the 61 strongest geo-climatic gradient in each dataset aimed to reduce the strength of natural 62 descriptors relative to land use. Although data sub-setting can highlight land use effects on 63 freshwater biodiversity, sub-setting our data often failed to produce stronger land use effects. 64There was no increase in spatial congruence in the subsets, suggesting that the observed land 65 use effects were not dependent upon the spatial extent of the subsets.
Extreme summertime flood events are expected to become more frequent in European rivers due to climate change. In temperate areas, where winter floods are common, extreme floods occurring in summer, a period of high physiological activity, may seriously impact floodplain ecosystems. Here we report on the effects of the 2002 extreme summer flood on flora and fauna of the riverine grasslands of the Middle Elbe (Germany), comparing pre- and post-flooding data collected by identical methods. Plants, mollusks, and carabid beetles differed considerably in their response in terms of abundance and diversity. Plants and mollusks, displaying morphological and behavioral adaptations to flooding, showed higher survival rates than the carabid beetles, the adaptation strategies of which were mainly linked to life history. Our results illustrate the complexity of responses of floodplain organisms to extreme flood events. They demonstrate that the efficiency of resistance and resilience strategies is widely dependent on the mode of adaptation.
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