Geology's role in zoonoses outbreaks
Research Background
Rock hyraxes (Procavia capensis) are medium-sized mammals that inhabit crevices in rock mounds or outcrops, where they find refuge from predators and extreme weather conditions. Native to Israel and the Palestinian Territories, their distribution has been expanding in the last few decades, correlated to land-use changes associated with rock excavation and the creation of artificial rock piles. Their expansion near human settlements is considered a risk to human health as the hyrax is a reservoir host of Leishmania tropica, a pathogenic protozoon causing leishmaniosis which can be transmitted to humans via sandflies. This increased risk to human health necessitates an understanding of the hyrax dispersion dynamics in order to designate effective control measures. The Judean Mountains of the West Bank have become a focal expansion area for hyraxes, which have dispersed from their historical range on the sparsely human-populated eastern slopes to the densely populated ridge and western slopes. However, despite the seemingly similar climatic and terrain conditions along their expansion routes across the ridge, observation records indicate that the hyrax populations have expanded at varying rates at different regions of the mountains.
This increased risk to human health necessitates an understanding of the hyrax dispersion dynamics in order to designate effective control measures. The Judean Mountains of the West Bank have become a focal expansion area for hyraxes, which have dispersed from their historical range on the sparsely human-populated eastern slopes to the densely populated ridge and western slopes.
However, despite the seemingly similar climatic and terrain conditions along their expansion routes across the ridge, observation records indicate that the hyrax populations have expanded at varying rates at different regions of the mountains.
Research Questions
We suggest that these differences in expansion patterns represent differences in shelter availability and dispersal possibilities, governed mainly by geology–land-use interactions. We hypothesized that the hyrax expansion patterns are modified by a combination of two key factors: (1) geological diversity, in which only specific rock formations are able to break down into large boulders suitable for hyraxes and (2) an external force able to break up the rocky foundation. Such force can be natural—erosion in steep areas or geological faults, or due to anthropogenic land-use change—such as infrastructure construction, road paving or quarrying. We predicted that novel habitats created by the interaction of geology with land-use change would create stepping-stone refugia that enable the hyrax to cross the mountains and disperse on the western slopes. Based on our assumptions, we developed a method to exploit geological data to define areas that have the potential to form hyrax habitats. We combined this with environmental and land-use change data, to determine how these affect the expansion patterns revealed by the hyrax observation records. The results provide further insight into a relatively little studied aspect of the interaction between geology and land-use change.
Results
The probabilistic distribution map of the full model with the marking of built-up areas enabled the detection of four factors that can explain the hyrax dispersal patterns and the differences in expansion between the northern, central and southern populations: (a) regions with suitable conditions on the eastern slopes, such as canyons and cliffs, are closer to the ridgeline in the north and central areas, but far from the ridgeline in the south; (b) regions with suitable conditions for hyrax settlement on the western slopes are large in the north and the center but small in the south; (c) possible movement corridors along roads and human settlements, which enable hyrax dispersion across the ridgeline in otherwise unsuitable environmental conditions, are found in the north and the center; and (d) large, continuous urban areas that hinder hyrax movement in the central and southern populations, but not in the north.
