Table 1.

Explanatory variables ranked according to their independent effect. I is the percentage of explained variance accounted for by the variable calculated using a hierarchical partitioning analysis performed with the tick, small mammals and Peromyscus leucopus variables as explanatory variables and the probability of occurrence of Borrelia burgdorferi as the response variable.

Variable	I (%)	Z-score
Prevalence L	20.06	7.83*
Total T	14.86	4.13*
Questing T	13.30	3.95*
Feeding L	9.75	2.46*
Prevalence M	9.56	3.25*
Burden L	6.79	1.81*
Diversity	5.61	1.30
Burden M	4.49	0.64
Proportion	4.36	0.78
Density M	4.24	0.78
Richness	3.90	0.55
Density L	3.06	0.13

Prevalence L: number of individual P. leucopus carrying ticks per total number of individual small mammal captured at a site, Total T: Number of ticks collected at a site both in the vegetation and on small mammals and of all life stages, Questing T: Number of ticks of all life stages collected in the vegetation at a site, Feeding L: Number of larvae collected on small mammals at a site divided by the number of trap nights, Prevalence M: number of individual small mammal carrying ticks per total number of individual small mammal captured at a site, Burden L: mean number of ticks feeding per P. leucopus individual captured at a site, Diversity: small mammal diversity at a site estimated with the Shannon index, Burden M: mean number of ticks feeding per small mammal individual captured at a site, Proportion: proportion of P. leucopus in the community relative to other small mammal species, Density M: mean number of small mammal individuals captured at a site per night per unit area (1 km²), Richness: total number of small mammal species at a site, Density L: mean number of P. leucopus individuals captured at a site per night per unit area (1 km²).

 Z-scores were calculated to estimate the significance level of I for each explanatory variable, using 1000 randomizations and significant variables are in bold (*P < 0.05).