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Results

From the 76 trees studied, a total of 21280 (mean=280.12, min=95, max=1005) saproxylic individuals were recorded and 254 (mean=46.01, min=32, max=62) species were found and identified (171 species were obligate and 82  were facultative). When removing singletons from the data before conducting multivariate analyses, I ended up with 201 species (mean=45.32, min=31, max=61). Out of these 201, 136 were obligate saproxylic species and 65 facultative species. 21280 (mean=279.3, min=94, max=1004) individuals were left when removing singletons.

Multivariate analysis

Using CCA, the results show more of an effect on species composition by Forest regrowth, Canopy cover and Trunk circumference than the other two variables which, as shown in Figure 3, had low impact in the model. The total level of explanation by our environmental parameters was shown to be 8.65 % (n=76, df=5).

CCA with species and all the environmental variables used in this study.

According to a permutation test based on the CCA for all species versus explanatory factors used in the study where terms were added sequentially (first to last), Trunk circumference (F=1.47, p=0.004) and Forest regrowth (F=1.41, p=0.008) were shown to have the highest impact on the data when removed or added to the model (999 permutations).

The CCA for obligate and facultative species separately showed Forest regrowth (F=1.37, p=0.023) to be the only significant explanatory variable investigating facultative species. Trunk circumference and Forest regrowth were found to be significant for obligate species (F=1.61, p=0.002 and F=1.39, p=0.018 respectively). For facultative and obligate species, this model explained 8.20 and 8.84 % respectively of the variation in beetle composition.

When dividing all species and individuals into the nine different guilds and running CCA tests for species and individuals separately I found that the explanatory factors explained 10.2 % (df=5) of the variation for species and 14 % (df=5) for individuals. No significant parameters were found on species level, closest was Forest regrowth (F=1.90, p=0.061). On individual level Trunk circumference (F=4.20, p=0.036) was the only significant variable.

CCA for all environmental variables and the number of species in each guild.

Genreral flying activity

Investigating the correlation between the number of non-saproxylic individuals found and the number of saproxylic individuals found (including singletons), no significance was detected (t=-0.484, p=0.63). Same result was found when looking at individuals not living on oak versus number of saproxylic individuals (including singletons) (t=1.144, p=0.256). When investigating species diversity and the influence of the explanatory variables, no significance was found.

Red listed species

A total of 23 red listed species were found in the study (NT=17, VU=6) and the total amount of red listed individuals found were 491 (mean=6.46, SD=5.20). Number of red listed saproxylic species per tree ranged between 0 and 10 and the number of red listed individuals per tree ranged between 0 and 33. When analyzed with the explanatory variables, no significant variables were found for the number of red listed species or individuals.

Individual species

General linear models for all species were done and significant results are shown in the table below. 

  Canopy cover Cavity size Level from ground Trunk circumference
Species Estimate p value Estimate p value Estimate p value Estimate p value
Aleochara stichai 0,058 NS 0,000 NS 0,000 NS 0,006 NS
Alosterna tabacicolor 0,022 NS 0,000 NS -0,004 0,048 0,001 NS
Ampedus cardinalis -0,014 NS 0,000 NS -0,001 NS 0,007 0,015
Ampedus hjorti 0,069 0,014 0,000 NS -0,002 NS 0,010 0,002
Anisotoma humeralis -0,003 NS 0,000 NS -0,004 0,049 0,004 NS
Anthrenus scrophulariae 0,048 NS 0,000 NS 0,003 NS 0,005 NS
Atheta crassicornis -0,025 NS 0,000 NS -0,005 0,035 0,004 NS
Attagenus pellio -0,077 0,020 0,000 NS -0,002 NS -0,006 NS
Aulonothroscus brevicollis 0,026 NS 0,000 NS 0,003 NS 0,011 0,045
Cortinicara gibbosa 0,044 NS 0,000 NS -0,004 0,042 -0,002 NS
Dasytes aeratus -0,066 0,013 0,000 NS 0,001 NS -0,001 NS
Dasytes caeruleus 0,018 NS 0,000 NS 0,000 NS -0,008 0,033
Enicmus fungicola 0,048 NS 0,000 NS -0,001 NS 0,008 0,023
Enicmus rugosus 0,027 NS 0,000 NS -0,004 0,023 0,000 NS
Enicmus testaceus 0,041 NS 0,000 NS -0,008 0,006 0,006 NS
Epuraea guttata -0,064 0,012 0,000 NS -0,002 NS 0,001 NS
Euglenes oculatus 0,041 NS 0,000 0,049 0,000 NS 0,005 NS
Gastrallus immarginatus -0,001 NS 0,000 NS 0,000 NS -0,007 0,009
Globicornis nigripes -0,062 0,018 0,000 NS -0,001 NS -0,003 NS
Korynetes caeruleus 0,004 NS 0,000 NS 0,000 NS 0,009 0,016
Latridius hirtus 0,037 NS 0,000 NS -0,002 NS 0,006 NS
Lordithon lunulatus 0,068 0,044 0,000 NS -0,005 NS 0,001 NS
Lymexylon navale 0,049 NS 0,000 NS 0,000 NS 0,003 NS
Megatoma undata -0,074 0,018 0,000 NS -0,002 NS 0,004 NS
Mycetochara axillaris -0,083 0,021 0,000 NS 0,002 NS 0,004 NS
Mycetochara maura 0,068 0,023 0,000 NS 0,001 NS 0,002 NS
Orchesia micans -0,009 NS 0,000 NS -0,001 NS -0,008 0,019
Osmoderma eremita 0,086 NS 0,000 NS 0,001 NS 0,000 NS
Phloiotrya rufipes 0,190 0,032 0,000 NS 0,006 NS 0,007 NS
Protaetia marmorata -0,027 NS 0,000 NS 0,003 NS -0,012 0,001
Protaetia metallica -0,053 0,038 0,000 NS 0,000 NS -0,005 0,042
Ptinus fur 0,069 0,042 0,000 NS -0,003 NS 0,006 NS
Quedius dilatatus -0,025 NS 0,000 0,014 0,002 NS 0,001 NS
Quedius mesomelinus 0,092 NS 0,000 NS -0,006 0,045 -0,002 NS
Quedius xanthopus 0,091 0,044 0,000 NS 0,000 NS 0,003 NS
Stictoleptura maculicornis -0,003 NS 0,000 NS -0,001 NS -0,026 0,011
Thamiaraea cinnamomea -0,058 0,026 0,000 NS 0,001 NS 0,004 NS
Trichoceble memnonia 0,091 0,006 0,000 NS -0,001 NS 0,001 NS


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Last updated: 05/10/19