Figure 1.
The study was conducted in two river catchment areas; Vestre Jakobselva (VJ) and Komagelva (KO), in low-arctic tundra zone of north-eastern Norway. We established 26 (VJ) and 24 (KO) sampling grids (15 m×15 m), distributed in pairs in heath and meadow habitat throughout major parts of each catchment. In each sampling grid, we estimated plant biomass in 13 plots and small rodent density with 12 traps, 3 per grid corner.
Figure 2.
Vole diets, selectivity and food availability based on plant functional groups.
To the left grey-sided voles (Myodes rufocanus, n = 81) and heath vegetation, to the right tundra voles (Microtus oeconomus, n = 66) and meadow vegetation. Upper panels show proportions in diets, middle panels selectivity index and lower panels proportions in vegetation biomass. Selectivity index has been calculated as ratio between diet and vegetation proportions using compositional analysis; see methods for details. Index values above zero indicate preference whereas values below zero avoidance. Black line represents median, boxes first and third quartiles, whiskers either maximum values or 1.5 times interquartile range (whichever is smaller) and points outliers. Numbers below vegetation proportions represent the actual range of biomass (g/m) per group.
Table 1.
Vole density index during 2007 at Varanger peninsula.
Figure 3.
Vole diets, selectivity and food availability based on plant families.
To the left grey-sided voles (Myodes rufocanus, n = 81) and heath vegetation, to the right tundra voles (Microtus oeconomus, n = 66) and meadow vegetation. Upper panels show proportions in diets, middle panels selectivity index and lower panels proportions in vegetation biomass. Selectivity index has been calculated as ratio between diet and vegetation proportions using compositional analysis; see methods for details. Index values above zero indicate preference whereas values below zero avoidance. Black line represents median, boxes first and third quartiles, whiskers either maximum values or 1.5 times interquartile range (whichever is smaller) and points outliers. Plant families are grouped according to functional groups.
Table 2.
Effect of food availability, season and river catchment on grey-sided vole diets.
Table 3.
Effect of food availability, season and river catchment on grey-sided vole selectivity.
Table 4.
Effect of food availability, season and river catchment on tundra vole diets.
Table 5.
Effect of food availability, season and river catchment on tundra vole selectivity.