The Giant Root-rat (Tachyoryctes macrocephalus) as a Synanthropic Landscape Engineer in the Bale Mountains, Southeast Ethiopia
Subterranean rodents particularly can act as ecosystem engineers by shaping the landscape due to soil perturbation and herbivory. Human activities, such as settlement establishment and livestock grazing, also profoundly impact ecosystem structure and functioning. In the face of growing local landuse...
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|Summary:||Subterranean rodents particularly can act as ecosystem engineers by shaping the landscape due to soil perturbation and herbivory. Human activities, such as settlement establishment and livestock grazing, also profoundly impact ecosystem structure and functioning. In the face of growing local landuse changes, understanding the effects of rodents engineering on biodiversity and how these effects are modulated by environmental factors and human activities is important to predict future changes, and even to reconstruct ecosystem history, as well as to implement sustainable management strategies.
Subterranean rodent engineering leads to increased landscape heterogeneity and nutrient availability for plants. Rodents also directly impact vegetation though foraging and burying small plants underneath mounds. As such, engineering activities of rodents affect plant and animal communities and ecosystem structure and functioning. However, rodent engineering activities and thus their effects are influenced by environmental conditions, vegetation and human activities. The effects of rodents and underlying mechanisms even became more complex in the areas where the distribution of engineering rodents and livestock grazing overlaps. This is because both rodents and livestock affect, and are affected by vegetation, on the one hand, and plant responses to such interactive disturbances depend on their functional traits, on the other hand. Disentangling this complex interplay between subterranean rodents, vegetation, human activities and their environment remains challenging.
In this thesis, I analysed the interplay of abiotic conditions, vegetation structural and functional composition and human land-use and the burrow density of the giant root-rat (Tachyoryctes macrocephalus RÜPPELL 1842), a subterranean rodent endemic to the Afroalpine ecosystem of the Bale Mountains in south-east Ethiopia. I first examined the effects of giant root-rat on plant species richness and vegetation cover and vice-versa, and how these reciprocal effects might be modulated by temperature, habitat wetness and livestock grazing. Secondly I focussed on the interplay between root-rat disturbance and human disturbance by working along a gradient of human activities. Finally, to understand the mechanisms through which root-rat engineering and human settlement and livestock grazing influence plant community assembly, I evaluated the changes in functional trait diversity and composition of vegetation communities along gradients of the engineering disturbances and human activities.
My thesis showed that increasing root-rat burrow density led to decreased vegetation cover; and reciprocally, increasing vegetation cover leads to decreased root-burrow density. Increasing livestock grazing intensity indirectly, via its negative effect on vegetation cover, leads to increased root-rat burrow density. Furthermore, increasing both root-rat engineering and human activities result in increased overall plant species functional dispersion. However, root-rat disturbances filtered plants with higher seed mass, stolonifereous vegetative organ and prostrate stem shot growth form, while human disturbances filtered species with larger leaf area and higher leaf nitrogen content.
This thesis promotes our understanding of the interplay between engineer rodents, human disturbances and local environmental conditions in shaping ecosystem structure and functioning. The thesis also demonstrates that giant root-rats play a synanthropic engineering role that affects vegetation structure and ecosystem processes in the critically important alpine ecosystem of the Bale Mountains. My findings also suggest that giant root-rats might have been benefited from human settlement and livestock grazing, as they reduce vegetation cover and height, particularly in enlarging the rodent’s open habitat.|
|Physical Description:||133 Pages|