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Metapopulation surveys and analysis

In the metapopulation part of GREENVEINS, the intention was to survey the effect of within LTS spatial structure on a number of species in detail and try to derive general trends in the relationship between spatial habitat structure and the spatial scale of population structure of species. Species selected for the analysis were the insects Dark Bush Cricket (Pholidoptera griseoaptera) Ringlet (Aphantopus hyperanthus), Orange Tip (Anthocharis cardamines) and Speckled Wood (Pararge aegeria), the plants Geum urbanum, Silene dioica and Teucrium scorodonia and the amphibians Tree Frog (Hyla arboraea) and Crested Newt (Triturus cristatus). Not all species were found to be present in enough LTSes to allow proper analysis.

For Pararge aegeria, Aphantopus hyperanthus and Geum urbanum enough observations were present to run a complete analysis including point observations within landscape test sites, using presence/absence on spots as dependent variable and spot-specific independent variables next to variables known only at test site level. To this data a linear mixed model was fitted.

For all three species, habitat cohesion ( measured as the exponentially distance weighted habitat amount in a 250m circle around the observation points) was a significant factor in explaining presence. For Aphantopus hyperanthus significance was lowest, and it was the only factor in the model. For Geum the LTS level amount of herbaceous GV was also a significantly positive factor, while the presence of Pararge aegeria was negatively affected by insecticide.

Single species surveys and analysis:
For the crested newt, an analysis of the relationship between terrestrial habitat, pond density and presence of the species in reproduction ponds was carried out, using existing data gathered for an area just outside one of the Dutch LTS. The resulting model was used to try to link the presence of the species in the three LTSes where it was found to the combination of model results and LUI. The same was done for the Tree frog, using an existing model. Results were so far inconclusive.

For Pholidoptera griseoaptera, a Capture-Mark-Recapture study was carried out at four locations within an LTS in Switzerland. The locations differed in LUI and LS. The study revealed that movement patterns were influenced by the structure of both habitat and the matrixx of unsuitable habitat in between. P. griseoaptera was able to cover unexpectedly large distances, especially in landscapes with a large share of unsuitable habitats which they were found to cross very fast. The hypothesis that the observed rates of dispersal result in frequent inter-patch movement is supported by a genetic survey on P. griseoaptera in the same area (Diekötter et al., abstract xx). At a local scale, with 2.4 km separating the most distant sampling locations, no significant population structuring was observed. Yet, a different pattern was found in an agricultural landscape showing a different landscape structure, more recent fragmentation of woody elements, and higher land-use intensity. Overall genetic diversity was lower and local populations of P. griseoaptera were genetically different from each other, possibly indicating a lack of inter-patch dispersal (Diekötter et al., abstract xx).

For Pararge aegeria, the available data was split up in two scenario’s,
- The High abundance scenario was characterized by beneficial environmental and weather conditions coinciding with high local abundance of P. aegeria.
- The Low abundance scenario reflected environmental stress and adverse weather conditions during larval development coinciding with low local abundance. In the high abundance scenario, P. aegeria was predicted to occur nearly anywhere under beneficial conditions.

In the low abundance scenario P. aegeria was restricted to high quality patches and landscapes. This showed that the sensitivity of P. aegeria to local and landscape features might change under adverse conditions, where alleged less important factors could turn into limiting ones. This result is in line with the interaction between LUI stress factors and LS that was found in species our species richness and community similarity analysis. It stresses the importance of high quality landscape conditions even for species that appear to be relatively tolerant, and sounds a note of caution when predicting population response for management purposes based on just a single (or a few) year(s) of observation.

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