Browsing by Person "Erhardt, Stefanie"

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The garden dormouse (Eliomys quercinus): ecology, habitat requirements and threats
(2025) Erhardt, Stefanie; Fietz, Joanna
Global biodiversity is declining rapidly, mainly as a result of anthropogenic pressures. Changes in land, such as deforestation and conversion to agriculture, are the main drivers of biodiversity loss, followed by direct exploitation such as hunting. Climate change and pollution are also contributing factors. The garden dormouse (Eliomys quercinus, Gliridae) is a small mammalian hibernator that has disappeared from more than 50% of its former range in recent decades, mainly in Eastern and Central Europe. The reasons for this decline are not yet fully understood. However, information on its biology, ecology, habitat requirements, and potential threats is needed to implement targeted conservation measures. To address this lack of knowledge, this study focuses on: 1. Filling knowledge gaps in the reproductive biology of the garden dormouse, including its genetic mating system and the timing of reproduction and hibernation (phenology), to better understand its life history strategies. 2. Identifying essential resources for the garden dormouse within the mountain forest, by investigating nesting behavior, home range use, and feeding ecology. 3. Characterizing potential threats for this species within the coniferous mountain forest by investigating the effects of climate change, the loss of essential resources, and habitat fragmentation. Therefore, a capture-mark-recapture study of the garden dormouse was conducted in the Northern Black Forest, one of its last natural distribution areas in Germany. To investigate the reproductive biology and the mating system of the garden dormouse, parentage analyses using five polymorphic microsatellite markers were combined with morphometric and behavioral data. Phenology was analyzed using capture-mark-recapture data in combination with morphometric measurements. To identify key resources during different life history stages, diet composition analysis in fecal samples and home range use and daytime resting sites were investigated by radio telemetry. Potential threats to the species were assessed by analyzing changes in body mass – used as a proxy for fitness – between two time periods (2003-2005 and 2018-2021), and by evaluating the effect of ambient winter temperatures on post-hibernation body mass. Based on the movement patterns of radio-tracked individuals, potential barrier effects of forest paths and trails were investigated. Genetic analyses and indirect indicators revealed that the garden dormouse is promiscuous. Typically for a promiscuous species garden dormice have relatively large testes and minimal sexual dimorphism. Males have extensive home ranges that overlap with those of several females, increasing the probability of mating encounters. This mating system maintains genetic variability, helping to avoid inbreeding and promotes offspring fitness. Garden dormice showed two birth peaks per year between 2003 and 2005, in contrast to only one birth peak in 2018-2021. Late-born juveniles grew faster to build sufficient fat reserves necessary for hibernation survival. The later onset of pre-hibernation fattening observed in adult females compared to adult males suggests that females must compensate for their higher energy demands during reproduction before hibernation starts. The home range provides essential resources for survival and reproduction, including food, resting sites, and mating partners. Garden dormice in the Black Forest showed a median home range size of 3.8 ha, with resting sites used in nest boxes and ground holes. However, ground holes were used more frequently during reproduction and low ambient temperatures, and are therefore an important resource especially during periods of high energy demand. The results of this study show that garden dormice are omnivorous with a preference for arthropods during the critical life history stages of juvenile growth and pre-hibernation fattening. Analyses of the crossing behavior showed that that adult garden dormice avoided crossing 4 m wide forest paths, which poses a significant threat to their survival by limiting their ability to colonize new areas, inhibiting gene flow and mate finding. In addition, this study also found that from 2018 to 2021, garden dormice had a reduced body mass during pre-hibernation fattening and growth compared to 2003 to 2005. As arthropods are the main food resource during this period, the ongoing insect decline may already be negatively affecting the availability of essential food resources, thereby reducing the survival probability of this population. This study found no effect of ambient temperature on post-hibernation body mass or phenology; however, the study sites were located at high altitudes where winters are still cold enough to ensure suitable hibernation conditions for garden dormice. Nonetheless, the ongoing climate change trends are predicted to further elevate winter temperatures even at higher altitudes, which could reduce the survival chances of this population in the future. To support the long-term survival of the garden dormouse, conservation measures should focus on the reduction of habitat fragmentation by rebuilding forest paths or, where this is not possible, creating underpasses with sufficient cover and connection to the surrounding habitat to facilitate dispersal and promiscuous mating. In addition, to support the garden dormouse during critical life history stages and to increase overall forest biodiversity and resilience, it is important to support food resources, especially arthropods, and resting sites by promoting forest structural diversity, increasing the amount of dead wood, and reducing pesticide use in the forest and the surrounding agricultural areas. In addition, natural resting sites such as ground holes should be supported by reducing the use of heavy timber machines and preserving structural habitat features such as rock crevices, underground burrows, tree holes, and cavities in dead wood. Implementing these conservation measures can mitigate the population decline of garden dormice. Reducing barrier effects, maintaining insect diversity and high structural diversity within forests can promote forest ecosystem resilience and support overall biodiversity.
Habitat requirements and home range use of the threatened garden dormouse (Eliomys quercinus) in a coniferous forest
(2025) Erhardt, Stefanie; Pfister, Jan; Beier, Marieke; Vorderbrügge, Rieke; Förschler, Marc I.; Fietz, Joanna
Understanding habitat use and requirements is essential for the conservation of endangered species, such as the garden dormouse (Eliomys quercinus). Therefore, we radio-tracked garden dormice (n = 39) in the Black Forest National Park (Germany) between 2019 and 2021, determined home range size by calculating autocorrelated kernel density estimates, located resting sites during the day, and analyzed their resting behavior. Furthermore, we investigated their crossing behavior across paths varying in width, in the degree of canopy closure, and understory. Median home range size was 3.8 ha (Q25 = 2.3 ha, Q75 = 6.6 ha) in adults and 1.9 ha in juveniles. Adult males increased their home range sizes during reproduction. In September, shortly before hibernation, adults used smaller home ranges, likely to save energy. During the day, garden dormice used nest boxes and natural nests under the ground as resting sites. Ground holes were an important resource as they were most frequently used by reproductive individuals and also at low ambient temperatures (0.1–14.7 °C). In contrast, nest boxes were used only at higher ambient temperatures (> 5.9 °C). Forest trails with tree cover and/or undergrowth were frequently crossed by adults, while 4 m wide forest paths without tree cover or undergrowth were rarely crossed. The results of our study show that the preservation of natural resting sites, the restoration of forest trails, or the installation of crossing structures are important conservation measures for the garden dormouse, facilitating migration and colonization of new habitats and reducing the risk to lose genetic variability.
Reduced body mass in a highly insectivorous mammal, the garden dormouse — ecological consequences of insect decline?
(2025) Erhardt, Stefanie; Förschler, Marc I.; Fietz, Joanna
Biodiversity is decreasing worldwide, and early indicators are needed to identify endangered populations before they start to decline in abundance. In mammals, body mass (BM) is regarded as an indicator of fitness, and its loss is used as an early warning signal preceding population decline. The garden dormouse ( Eliomys quercinus , Gliridae, BM: 60–110 g) is a small mammalian hibernator that has disappeared from over 50% of its former range in the last decades. The aim of this study was to investigate whether garden dormice from a presumably thriving and stable population already show early warning signals, which may precede a population decline. We therefore conducted capture‐mark‐recapture studies during 2003–2005 (Period 1) and 2018–2021 (Period 2) in the Northern Black Forest, one of its last natural distribution areas in Germany. We collected fecal samples, measured BM, and tibia length as a proxy for size and age. Results revealed that in Period 2 adult dormice had a significantly lower (12%) pre‐hibernation BM, corrected for body size, and juveniles showed a significantly lower BM gain after weaning than nearly two decades ago. Fecal samples collected in Period 2 showed that arthropods represented the main food residues in fecal samples during juvenile growth and pre‐hibernation fattening. Ambient temperature during hibernation showed no correlation with BM at emergence. We could not detect a phenological time shift in reproduction; however, we found only one birth peak in Period 2, compared with two birth peaks in Period 1. Observed changes in BM and reproduction pattern represent early warning signals, as they point to an insufficient availability of high‐quality food, which prevents dormice from meeting their nutritional requirements, with potentially serious consequences for their reproductive success and survival. As arthropods are the dominant food resource, their decline may at least partly explain this phenomenon.