The ecology of Central European non-arboreal ants – 37 years of a broad-spectrum analysis under permanent taxonomic control:

Methods: A broad spectrum analysis on ant ecology was carried out in the years 1979 to 2015, including 232 study plots in Central Europe within 46.5° N to 54.1° N, 9.3°E to 15.6°E and from 5 to 2382 meters above sea level. Basically each type of terrestrial, non-arboreal habitat in which ants are able to reproduce was investigated and the full environmental gradient for almost each environmental variable was covered. The whole study was under consistent taxonomic control, assisted by holding of a permanent and curated museum collection with updating of the data regarding newly discovered cryptic species. Recording of ant biodiversity and abundance was thoroughly based on direct localization of altogether 17,000 nest sites with determination of nest density per unit area. Two new methods for estimation of ant biomass and ant species richness are introduced. A total of 17 niche dimensions were recorded: 6 physico-chemical factors, 7 structural factors and 4 species-defined factors. The paper represents the first ecological study with a broad and thorough application of the soil temperature determination system CalibSoil which will allow future ecologists comparable determinations of the thermal behavior of hypo- and epigaean organisms within the context of global warming. It is shown that approximations of fundamental niche space and fundamental niche overlap are possible from field data on the basis of three factors: (a) temporal disclosure of hidden fundamental niche space during dynamic processes, (b) mathematic decoupling of fundamental niche space from particular study plot situations by subdivision of niche dimensions into classes and (c) idealization of niche space by smoothing of frequency distributions for all niche variables. A method to estimate interspecific competitive exclusion based on a model that relates realized niche overlap to fundamental niche overlap is provided. Results: Thanks to the very broad environmental gradients considered and the high number of data points, it was possible to show highly significant relations of species richness and ant biomass of ant assemblages to nearly each investigated environmental variable. The curve characteristics of these relations resembled in the majority of cases skewed or unskewed optimum curves whereas linear or quasi-linear relations were rare. The most important factors directing niche segregation of ants in the temperate zone are soil moisture and maximum and mean soil temperature whereas herb-layer phytodensity, ranking at the penultimate place among 12 assessed environmental variables, is thought to have mainly an indirect, but very strong, effect by altering moisture and temperature conditions. The distribution of 86 individual ant species relative to environmental variables is shown. 27 categories or types of habitat were compared for species richness and biomass. By far the highest species richness and the highest biomass for open land habitats was found in xerothermous to mesoxerophytic grasslands on limestone or chalk with a mean value of 13.1 species/100 m² and 8.8 g fresh weight/m². Within the woodland habitats, the highest species richness and biomass was achieved with 12.5 species/100 m² and 5.5 g fresh weight/m² in xerothermous to tempered Quercus wood whereas mature Fagus woods (0.35 species/100 m², 0.07 g fresh weight/m²) and Picea-abies-dominated woodland (0.63 species/100 m², 0.27 g fresh weight/m²) showed the poorest ant assemblages. Convincing evidence was presented for the theory of E. Odum that narrow niche spaces increase the number of species a habitat may hold and that species richness and evenness show a clear positive correlation for ant assemblages consisting of more than 5 species/100 m². Strong statistical evidence is provided that interspecific competitive exclusion increases with growing relatedness: 20 pairs of closely related species (the collective SIBLIN) had significantly lower coexistence values than 232 congeneric pairs of all other species from only the genera to which the collective SIBLIN belonged (ANOVA F1,232 = 9.98, p < 0.002). It was shown that 22–31 % of variance of mean seasonal soil temperature TMEAN was attributable to the habitat-specific factors stratification and density of phytolayers, orography (aspect) and properties of ground material. These data show that predictions of future zoogeographic shifts due to global warming based on meteorological simulations only will remain inaccurate as long as the habitat-dependent temperature component is neglected.