| Summary: | Climate change and human land-use strongly impacts ranges and distributional borders of dragonfly (Odonata) species which are therefore a good model group for understanding how the strength of such impacts depend on species specific ecology and functional traits. The specificity of their larvae to habitat type, their amphibious life cycle, and the ease of identification of the adult, combined with the good knowledge of their distribution and ecological requirement, make dragonfly species particularly well suited for studying effects of climate change and human land-use in the short term — which is related to structural changes of running and standing waters — and in the long term — which is related to species conservation and biogeography. A major challenge in conservation ecology is to understand interspecific differences in response to climate change and human land-use, i.e., what enables some species to persist while others decline? In this context, the main objective of my research was to investigate how current climate change and human land-use shape large scale distribution patterns of European dragonflies and whether these macroecological pattern and changes can be linked to functional traits such as taxonomy, habitat specificity, metabolic plasticity, and biogeographic traits such zoogeographical origin. In Paper I we describe how changes in species richness pattern across Europe correlate with range changes in different taxonomic and biogeographic groups of dragonflies. We found that true dragonfly (Anisoptera) species are driving local turnover in species ranges to a greater extent than damselfly (Zygoptera) species. We found that Tropical and Mediterranean species have expanded their distributional range to a much larger extent than the Eurasian and Boreo-alpine species. In Paper II we describe how the strength of impacts from current climate change and human land-use depend on habitat specificity of the dragonfly larvae. We found that species adapted to permanent standing (perennial lentic) water and temporary (running or standing) water, had larger ranges than the more specialized species adapted to permanent running (perennial lotic) water habitats. We found that species reproducing in temporary water track climate changes better than species adapted to permanent water. In Paper III we explore the relationship between metabolic plasticity (expressed as the ability to shift in voltinism) and latitudinal range of the distribution of European dragonfly species. We reviewed the relationship and found that latitudinal range increased with voltinism span, i.e., a considerable voltinism span allows certain species to occur under a larger range of climatic conditions than species with less metabolic plasticity. We conducted experimental ex-situ measurements of metabolic rates measured as respiration rates at 10°C and 20°C, respectively, of four Scandinavian dragonfly species. We used two species with a northern distribution, one with a southern distribution and one ubiquitous species. We found that the ubiquitous species was the only being able to regulate the metabolic rate along with the experimental temperature. The northern species had consistently low metabolic rates, and the southern had consistently high metabolic rate across the experimental temperatures. This indicates that one mechanism controlling the present distribution of dragonfly species in Europe is their ability to adjust metabolic rate along with a change in temperature. In Paper IV we present preliminary results of the first two years of the national dragonfly atlas survey about the distribution of all dragonfly species occurring in Denmark. During the past decades, changes have differed somewhat from the major trends of the last century. There has been a striking expansion of southern species until recently only rarely seen in Denmark, and also an obvious expansion of a number of less rare thermophilic species. However, the diverse fauna of standing mesotrophic and oligotrophic waters seems to some extent to have undergone a decline which may have been caused by habitat degradation and eutrophication. In Paper V we present the current status of the true dragonfly species Aeshna serrata in Denmark. It is known from a relatively wide geographical range, though in Europe it is mainly found around the Baltic Sea in Estonia, Finland and Sweden, and locally, away from the coast, in the remaining Fennoscandia. In recent decades, it has expanded westwards across the mainland in Sweden and the occurrence in Denmark is a likely result following a possible case of jump dispersal by individuals from the westward expanding Swedish populations. After it was found in Northern Jutland in 2006 it has expanded its range further and occurs now in several small populations. Our results suggest that especially Boreo-alpine species and habitat specialist, especially those in permanent running water habitats but also species in standing mesotrophic and oligotrophic water could face severe challenges in response to rapid climate change combined with ongoing loss and deterioration of habitat due human land-use, and this effect may also apply to the distribution of species from various functional groups in Southern Europe.
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