Does environmental adaptation or dispersal history explain the geographical distribution of and ticks in Finland?

In Finland, the distribution area of the taiga tick, (Schulze, 1930), is nested within a broader area of distribution of a congeneric species, the sheep tick, (Linnaeus, 1758) (Acari: Ixodidae). We assess whether distinct environmental adaptations or dispersal history provides a more parsimonious explanation for the differences in the distributions of the two common and medically important ixodids in Finland. We used an innovative spatially constrained randomization procedure to analyze whether crowdsourced occurrence data points of the two tick species had statistically different associations with any of the 28 environmental variables.