The perfect burrow for what?
CEES Extra seminar by Anne Laudisoit
Jirds and gerbils are known carriers of plague in semi deserts and desert belts extending across Central Asia to the Middle East and the North African arid regions. The jird species are mainly nocturnal and live in relatively simple burrow systems compared to diurnal R. opimus. It seems the rule that diurnal rodents construct more complex and extensive burrow systems than nocturnal species; the diurnal activity being usually correlated with sociality. The complex systems of R.opimus may contain one or more nesting and food chambers, or a combination of these structures. These burrows provide a specific, buffered, environment and refuge for other rodent species, and a number of invertebrate species, in particular the haematophagous ectoparasitic fauna (fleas, ticks, flies etc) that feed on rodent hosts and are potential vectors of diseases (plague, tularaemia, leishmaniasis etc). Burrows are also used by reptiles and birds, either as temporary refuge, winter shelters or nests.
Digging of new burrow systems may be related to rodent density and abundance, and soil structural characteristics (soil texture, hardness of top soil, slope) which are known to have a strong effect on burrow site selection in various species. However, burrow systems are not static units, and occupancy of a burrow may be related to a series of abiotic and biotic factors developing and evolving over time (e.g. from the first occupancy).
Burrowing rodents truly act as ecosystem engineers and increase landscape heterogeneity in arid grasslands but also affects the geomorphology on the 2 – 5 m scale level. For example, vegetation cover (plant species diversity and richness), soil physical and chemical properties, amount of stored organic matter, and diversity of soil microbiota will be modified by rodent activity (soil pedturbation). Later,burrow selection may be partly linked to rodent abundance/density, and availability of resources, but also to a series of factors such as abundance of free ectoparasites, time since previous occupancy, burrow age, quality of food or vegetation cover (influenced by soil and geology) at a fine local scale.
Knowing the importance of flea abundance in the epizootic process and the influence of rodent density/abundance on plague dynamics (dual thresholds), understanding what a perfect burrow is from a rodent or an ectoparasite perspective is relevant. Understanding why other sites are seldom selected or even abandoned is as relevant, since it could allow us to perceive what conditions are the least optimal for the epizootic triad components. In this study, the relations between the burrow characteristics and the burrow dwelling rodents are examined, by looking at environmental factors that may contribute to make the perfect burrow for hosts, pathogens and ectoparasites.