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B4) Saprophytic Beetles

Functional connectivity among saprophytic beetles in dead wood patches

Gernot Segelbacher
Doctoral researchers: Nathalie Winiger (since 2016) & Laura-Sophia Ruppert (since 2019)

University of Freiburg, Faculty of Environment & Natural Resources, Institute of Forest Sciences,
Chair of Wildlife Ecology and Management

Background

There is growing evidence that insects are not only declining in grasslands, but also in forest ecosystems, driven by large scale effects, such as the increasing fragmentation of suitable habitat. In Central European forests existing management practices have been focusing on retention of dead wood and habitat trees, which provide habitat for saproxylic species including several that are endangered. However, it remains unclear if this kind of management is helping to maintain species richness and genetic connectivity across forest landscapes Within that context we here focus on estimating species richness with molecular methods (metabarcoding) and identifying connectivity levels by genetic means.

 

Research questions and hypotheses

Here, we investigate arthropod diversity on our research plots in correlation to habitat type, retention forestry elements (such as dead wood abundance and forest heterogeneity) and connectivity of the surrounding landscape. Additionally, we investigate intra-population genetic diversity and inter-population genetic distance for arthropods with different dispersal ability (short-distance, medium-distance and long-distance dispersers) in order to characterize gene flow between populations as a function of habitat availability and quality and to infer thresholds for functional connectivity considering distance and landscape structure. We expect that:

  • Arthropod diversity estimates depend on local habitat diversity and is mainly affected by the available amount of dead wood and habitat trees.
  • Species richness measured by community metabarcoding can be predicted by the surrounding landscape matrix and the intensity of forest management.
  • Gene flow, and thus functional connectivity, is a function of inter-patch distance, with the effect size depending on the species' dispersal ability and the landscape permeability.

 

Approach, methods and linkages

Within B4, species are sampled on the ConFoBi plots, representing different amounts of dead wood, distance and forest types. Species diversity is estimated using both eDNA from different substrates and bulk sample metabarcoding approaches. For measuring intraspecific genetic diversity and distance SNPs called from RADseq data will be used to create matrices of genetic distance which can be correlated with habitat and landscape data. The landscape matrix characteristics (tree species composition, height, horizontal and vertical structuring) are obtained by aerial photographs and the amount of coarse woody debris between patches is quantified by a combination of terrestrial mapping and remote sensing (A1).
B4 is directly linked with B3 on sampling and analysing arthropod communities. Additionally, B4 is linked to A1 and A2 in making use of their data, mainly plot and landscape forest characteristics and with B1, B2, B5 and B6 in exchanging and combining data of the project specific taxa.

 

Findings

During the first three years, B4 started developing protocols for estimating deadwood beetle occurrence in deadwood through eDNA sampling of wood and for sampling eDNA from tree cavity mould to identify tree microhabitat inhabiting species. In combination with B3, flight interception traps have been set up to determine arthropod diversity and identify key target species for the genetic connectivity studies. Based on this, eight beetle species were chosen for RAD sequencing and are being analysed to estimate gene flow between populations.
In the second phase B4 will:

  • Characterize ground-dwelling arthropod communities in relation to habitat quality parameters like dead wood abundance/type, vegetation, soil chemistry and structural parameters like forest heterogeneity and connectivity. For this we will collect several leaf-litter sifts along a transect of each plot and process them as bulk samples in a metabarcoding pipeline to estimate arthropod species richness.
  • Build up on the preliminary results of the first phase on utilizing eDNA metabarcoding to identify arthropod communities inhabiting tree microhabitats. For this we will develop and test sampling protocols for a selection of tree microhabitat types based on the data of A2.
  • Continue to analyse the functional connectivity of arthropod populations within our research area with more species. In collaboration with B3 a species of cavity-nesting Hymenoptera will be chosen and collected to represent potential long-distance dispersers and additionally further beetle species will be added to the analysis from pitfall trap samples of B6. For the chosen species intraspecific genetic distances will be measured by calling SNPs from RADseq data.

 

Perspectives

In the future, B4 will focus on modelling functional connectivity by analysing the genetic diversity of key arthropod species across the whole study area and linking the biodiversity values of all plots assessed through metabarcoding with habitat quality across the ConFoBi scales. With that, we aim to estimate quantitative thresholds of dead wood on the local scales necessary to create functional connectivity across the landscape scale. Ultimately, disentangling the effects of local and landscape patterns on biodiversity will help to identify the main drivers for the ongoing insect decline in forest ecosystems.