title: Linking Scales: Investigations on the interaction between environmental conditions, humans, and a fossorial rodent species across space and time
title: Verknüpfung von Ebenen: Untersuchungen zur Interaktion zwischen Umweltbedingungen, Menschen und einer fossilen Nagetierart über Raum und Zeit
titleType: AlternativeTitle
Creators: name: Reuber, Victoria Michelle
Publisher: name: Philipps-Universität Marburg
Year: 2023
Subjects: path analyses
fossorial
population genetics
species-environment interactions
demographic history
afro-alpine
Life sciences
Biowissenschaften, Biologie
Bale
Giant root-rat
human impact

description: Interactions between species and their environment build the backbone of biodiversity and ecosystem stability. Species-environment interactions shape species' spatial distributions and population dynamics, with present and past environmental conditions, as well as evolutionary mechanisms such as dispersal ability playing pivotal roles. Understanding how species are shaped by the environment and human activities across spatial scales and time, is a precondition to predict and reverse the ongoing decline of global biodiversity.
Fossorial species usually exhibit a tight interaction with the environment. Their burrowing activity shapes ecosystems processes but at the same time, limits their ability to disperse. This may be exacerbated in mountain ecosystems where the geomorphology of the landscape further restricts dispersal and distribution ranges. Additionally, human induced habitat degradation and environmental change in mountain ecosystems may affect the persistence of many species.
In order to disentangle complex species-environment interactions under human activities, a combination of methods is required covering varying spatial scales, including how the environment over time has shaped the species we observe today. This thesis explores the case of the giant root-rat (Tachyoryctes macrocephalus), an endemic, fossorial rodent species with a limited range in the afro-alpine Bale Mountains in southern Ethiopia. By combining spatially explicit ecological and genetic analyses, I assessed the intricate interplay between the environmental conditions and human activities across time that have shaped the species’ local and range-wide distribution at the landscape scale, as well as its population genetic structure, diversity, and demography.
Through a combination of methods, my results revealed a scale dependency of species-environment interactions, with historical and evolutionary factors shaping interactions differently on local and landscape scales. Ecological field studies revealed (Chapter II) a tight interaction between the giant root-rat, the local environmental conditions and human land use. Giant root-rat activity reduced vegetation cover, while the local species' activity increased with decreasing vegetation cover and elevated livestock grazing, indicating the species' preference for open habitats. However, extending our inquiry to the landscape scale using satellite-based remote sensing and vegetation data (Chapter III), we found that texture metrics describing topographic differences across the landscape determined the species' range-wide distribution. Hence, environmental conditions shaping the local activities, differed from those influencing the species' overall distribution.
Population genetic studies of genetic subdivision and diversity (Chapter IV), further demonstrated the effect of topography on the species distribution and dispersal ability. I found a pronounced subdivision of the species into a northern and southern population, with no sign of gene flow between them. Landscape genetic analyses revealed that topographic barriers were the driving force on the landscape scale, hindering dispersal between north and south. Environmental conditions played a subordinate role, at least for local species’ genetic substructure and dispersal within populations.
With the analyses of giant root-rat subfossil remains from the Late Pleistocene era (Chapter V), I expanded the examination of the species’ interaction with the environment and humans on a temporal scale. Notably, radiocarbon dating of these subfossils provided insights into human presence in the Bale Mountains, indicating nearly continuous human habitation in the region from 47,000 to 31,000 years ago. Ancient DNA studies revealed that both environmental changes and human activities played pivotal roles in driving phylogenetic lineage divergence and shaping the demographic history of the species over thousands of years. The last glaciation of the Bale Mountains and human hunting practices during that period likely led to a population decline in the northern and southern regions, respectively. Additionally, I observed an ongoing population decline and reduced nucleotide diversity in the northern population since the end of the last glacial period, possibly resulting from habitat reduction caused by environmental changes.
The presented studies in this thesis collectively demonstrate the direct effect of local environmental conditions and human activity on the occurrence of the species. The joint consideration of my research findings emphasized that the giant root-rat may have a limited ability to shift its range under changing environments due to its limited dispersal ability, which hinders the traversal of pronounced topographic barriers in the landscape. Understanding these complex relationships is essential for effective conservation management for preserving mountain biodiversity and ecosystem functionality, of the afro-alpine ecosystem and other similar environments where species and their habitats are deeply interconnected.