Land use and climate change: Anthropogenic effects on arthropod communities and functional traits

Today, the world’s surface is strongly influenced by human activities and thus the present-day geological era has been termed the Anthropocene. One of the strongest anthropogenic drivers is land use influencing habitats and species worldwide. Additionally, global climate is shaped by human activities, and since climatic conditions have strong effects on the distribution and fitness of organisms, this is the also one of the most important anthropogenic impacts on ecosystems. Hence, both factors affect diversity of species and habitats, but also ecosystem functioning and services. Analysing species diversity is a well-established method to draw conclusions on ecosystem functioning, because the stability of ecosystems increases with species richness and abundance. It is also possible to measure species’ responses in ecosystems, using functional diversity as a predictor. Species traits are features or measurable properties that may be related to the effect or response of a species in an ecosystem (e.g. nutrition specialisation or distribution) and play an important role to determine functional diversity. In this thesis, I analyse and combine the effects of land use and temperature on arthropods in general but also on moths as a case study, which is an unattended but diverse taxonomic group. I consider different levels as (1) Arthropod communities in general, (2) moths as a functional group, (3) morphological variability of single species, and (4) physiological variability of single individuals and show how specialists and generalists differ in their response and effect traits and how these differences have effects on the different levels. Main parts of this thesis were performed in the Biodiversity-Exploratories, a research platform that focuses on effects of land-use intensity on biodiversity and ecological processes in forests and grasslands in three different regions in Germany The first study focussed on beech herbivory affected by harvesting intensity and beech dominance. For this purpose, we determined leaf damage and collected Arthropod herbivores in three different regions distributed across Germany. The results suggest a general negative effect of intensive land-use on forest herbivores and the strongest negative effect appeared early in the growing season. For the second and third study, we collected more than 5000 moths from the same three regions, and focussed on grasslands. We determined 461 different species, assigned several interspecific life-history traits (describing specialisation on resources or reproductive strategies), and additionally measured morphological traits (body mass and wing area) of more than 2000 individuals. In the second study, we analysed the effect of land-use intensity (as grazing, mowing and fertilisation) on species diversity and trait composition in moth communities. With increasing land-use intensity, a general decrease of species diversity across all regions was apparent, but also a shift to generalised species, which leads to functional homogenisation in ecosystems. Mowing had the strongest negative effect. The third study focused on intraspecific effects based on morphological changes with increasing land-use intensity. We found several species that benefit from the application of fertilisers due to an increasing body mass, which enhances reproduction success of insects. Such species are mostly generalists, but were still not able to increase their abundance in stronger managed habitats in contrast to other species. In the fourth study, we analysed transpiration and metabolic rate from 557 different arthropod individuals of forest and grassland sites. For this I developed a simple and effective method to measure water loss of several samples within a short period, which we describe in detail in this chapter. Specimen from grassland sites, representing arid habitats in contrast to forests, show generally lower water loss rates. These species developed strategies decreasing cuticular transpiration, resulting in a higher effect of respiratory transpiration on total water loss. In the fifth study, we kept caterpillars of 30 species in different temperature treatments analysing the survival and growth rate in response to the surrounding temperature. Additionally we measured transpiration and metabolic rate. All species showed in general a lower survival rate and increasing growth, transpiration and metabolic rate with higher temperature and especially specialists face a higher risk from increasing temperature. Hence, this thesis shows similar effects of land use and climate change, as both drivers lead to a general loss of diversity and a shift towards more generalistic communities. Communities of specialists are, however, important to decrease homogenisation and thus receive ecosystem functions. These results provide important information for national and international policies and to support the development of sustainable land-use methods and to reduce climate change