title: Temperate ant communities under anthropogenic impact
Creators: name: Grevé, Michael E.
Publisher: name: University of Bayreuth
Year: 2019
Subjects: subject: Ameisen
subject: Gemeinschaftsökologie
subject: Landnutzung
subject: 570
subject: 590

description: European, temperate terrestrial ecosystems are shaped and managed by humans since millennia. While grasslands were consistently managed at low intensities over centuries, forest management changed multiple times over time and each change had an immense impact on the structure of forest ecosystems. Since the last decades, the management in both biomes is changing, but in opposite directions. Today, highly diverse grasslands are threatened by land-use intensification, while reciprocally, forests are transformed from intensively used even-aged monocultures to uneven-aged multi-species stands in order to promote biodiversity. How species communities are affected by management and how they respond to changes, are key questions in ecology. But especially for some keystone taxa such as ants which are known to be responsive to management, they are still not sufficiently understood. In grasslands for example, the underlying mechanisms leading to a decrease in species richness as well as changes in functional community composition remain elusive. In forests, management has been shown to have an overall negative effect on ant communities in tropical, and a positive effect in boreal forests. However, in temperate forests, it is unclear what components of forest management affect ant communities and how. In my first manuscript, I studied the direct and indirect effects of land-use intensification on ant communities in temperate grasslands which were sampled on 110 grassland plots in three regions in Germany. The sampled grasslands are used as meadows or pastures, being mown, grazed or fertilized at different intensities. I found that ant species richness, functional trait space of communities and abundance of nests decreased with increasing land-use intensity. The land-use practice most harmful to ants was mowing, followed by heavy grazing by cattle. Fertilization did not strongly affect ant species richness. Grazing by sheep increased ant species richness. The effect of mowing differed between species and most rare species occurred mainly in plots managed at low intensity. The results show that mowing less frequently or later in the season would retain a higher ant species richness – similarly to most other grassland taxa. The transformation from pastures to intensively managed meadows and especially mowing directly affects ants via the destruction of nests and indirectly via loss of grassland heterogeneity (reduced plant species richness) and increased soil moisture by shading of fast-growing plant species. In my second manuscript, I explored the direct and indirect effects of forest management on the taxonomic and functional diversity of ant communities in 150 temperate forest stands in three regions in Germany. I analyzed the effects of 18 variables, including variables of forest management, forest structure, arthropod diversity, and biomass, as well as abiotic factors, on ant species richness, abundance, and functional trait diversity. Main direct effects of forest management on ant abundance and species richness were caused by tree species selection, measured as dominant tree species. The main positive indirect effect was mediated by a reduced canopy cover with an increasing proportion of oak and pine, which results in a higher temperature amplitude. Functional diversity, based on life-history traits, was affected positively by tree harvesting and negatively by structural complexity. This study shows that forest management practices in temperate forests strongly impact the ant community structure. This can be beneficial for ants if management reduces the canopy cover, either by tree harvesting or by changing the tree species composition towards shade-intolerant tree species. To promote ant diversity as key taxon for maintaining ecosystem processes in forest ecosystems, I suggest integrating forest stands with more open and warmer conditions in future management strategies. In my first two manuscripts, I could show that ant communities respond to changes in habitat structures and that species with certain (morphological and life-history) traits are more sensitive towards management intensification than others. Thus, the question arises whether traits can be used to predict how a species is affected by changes in habitat structures. Or in a broader view and based on other studies: how reliable are morphological traits as functional traits? I try to answer this question in my third manuscript where I investigated the running speed of differently sized ants (body size and leg length) along a surface rugosity gradient which represents different habitat structures. In general, it is thought that leg length is a good predictor for running speed and by theory, similarly sized species should respond similarly towards changes. But the opposite was the case and leg length was not a good predictor for running speed. In addition, similar-sized species responded idiosyncratically to high surface rugosity, which might be related to species-specific habitat preferences. This hampers precise predictions on how species might respond to changing habitats, based on morphological traits exclusively. Based on the findings of all three manuscripts, it is possible to make predictions of how future management will change species communities, but species-specific forecasts remain difficult.