perjantai 17. marraskuuta 2017

Field Study Plan for Mammalian Hosts of Ixodes Ticks (M-HIT)

Updated Nov. 29, 2017

Study goal. The aim is to clarify the interaction between ticks and mammals to develop ecological control methods for tick-borne diseases. It is generally agreed that in an ecosystem, the amount of large mammalian herbivores regulates the amount of ticks, and that the amount of small herbivores and birds regulates the disease prevalence in ticks. In the case of the northern boreal forest, the most common small herbivores are the voles. Another important feature to know is that since people favor herbivore game species, the amount of predators relative to herbivores is lower than in a natural ecosystem. In this study, we will try to quantify how much the amount and composition of each mammalian group affects the tick-host system. We are especially interested in how much red foxes affect the habitat use of voles which, in the presence of foxes, cannot freely roam all their preferred habitat, collecting ticks. From the tick point of view, this might mean fewer larvae developing into nymphs and less transfer of diseases, received and given.

Field study design. 6 study sites have been selected from the southern part of Finland (Figure 1). Each study site is a pair of game triangles, on one triangle there are lots of foxes and on the control there are less foxes. The area is climatically relatively homogeneous and also in the same phase of emergence i.e. the incidence of tick-borne diseases in the Finnish population has been growing rapidly in the recent years. (The official disease statistics www.thl.fi). The sites have also different amounts of cervids (moose Alces alces, white-tailed deer Odocoileus virginianus and roe deer Capreolus capreolus). Three of the sites are inland and three of them are close to the sea. The whitetail was introduced into Finland from North America as a game species, and its does very well in the southwestern Finland as does also roe deer. Moose is common in the whole of Finland in forested areas.

Field data collecting. In the winter hunters visit each game triangle and record the amount of snow tracks of mammals and the amount of game birds. The triangle system has originally been developed for estimating game numbers and the results are published yearly by Natural Resources Institute Finland (www.luke.fi). Vole trapping is made in the fall (main species being bank vole Myodes glareolus and field vole Microtus agrestis). This area is dominated by agricultural land which means that the interaction between field vole and red fox should be a dominant feature in the tick-host system. Tick collecting is made in the spring with the dragging cloth method (mainly Ixodes ricinus in this area). Data collecting is done on each game triangle on three vole habitats i.e. coniferous forest, clearcut and open field. The exact locations will be chosen based on the permits given by the land owners. On each habitat, there will be 3 small mammal triangles (15 meters x 15 meters). 12 mouse snap-traps will be placed at 5 meter intervals along the sides of the triangle (1 in each corner and two in between) for two nights in a row. Samples will be taken from the voles and ticks and sent to the University of Turku, to be analyzed for the diseases they carry. The volume of ant hills will also be recorded at the study sites.

Figure 1. Game triangle locations in Southern Finland. Green and yellow triangles are active and the red ones are not in use). Study locations are marked with blue circles on the map.

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