Features in and around residential gardens affecting the presence and abundance of questing Ixodes ricinus ticks

Figures & data

Figure 1. Study area with the 103 individual gardens (points with 500 m buffers) and land use units, such as agriculture, forest, water body, park or garden allotment, settlement, and street, which may affect the occurrence and abundance of questing Ixodes ricinus ticks. Source of land use data: German Authoritative Real Estate Cadastre Information System ALKIS® (LGLN - Landesamt für Geoinformation und Landesvermessung Niedersachsen, 2014).

Figure 2. Examples of the predictor variables on the garden level: vegetation type (a–e) including no vegetation (a), lawn (b), groundcover (c), hedge (d), and flower bed (e); vegetation density (f–h) including no vegetation (f), sparse vegetation (g), and dense vegetation (h); and ground type (i–k) including bare soil (i), litter (j), and vegetated ground (k).

Figure 3. Sampled gardens with minimum and maximum values of the landscape predictor variables, such as forest, agriculture, and sealed area, in their 500 m buffers. Source of land use data: German Authoritative Real Estate Cadastre Information System ALKIS® (LGLN - Landesamt für Geoinformation und Landesvermessung Niedersachsen, 2014).

Figure 4. Time series of meteorological covariates during the sampling period in 2015: daily mean air temperature, daily mean relative humidity, and daily precipitation sum. Sampling dates are given as vertical grey lines.

Table 1. Characteristics of potential predictor variables, covariates, and their distribution in and around 103 private gardens in the Braunschweig region. Garden-level predictor variables (In Figure 2 are several examples) characterizing the sample transects (n = 2,666).

Predictor variable	Factor levels	No. transects
Vegetation type	no vegetation	141
	lawn	697
	groundcover	316
	hedge	744
	flower/vegetablele bed	768
Vegetation density	no vegetation	189
	sparse	1,033
	dense	1,444
Ground type	bare soil	114
	litter	224
	vegetated	2,328
Compost type	no compost	2,471
	open	100
	closed	14
	deadwood	81
Shade	shaded	817
	not shaded	1,849

Table 2. Characteristics of potential predictor variables, covariates, and their distribution in and around 103 private gardens in the Braunschweig region. Landscape-level predictor variables. Proportions were determined within a 500 m buffer around the garden perimeter (see Figure 3 for gardens with minimum and maximum values of these variables).

	Proportion or distance
Predictor variable	Minimum	Maximum	Median
Proportion of
forest (ALKIS class 43,002)	0.00	0.53	0.01
agriculture (ALKIS class 43,001)	0.00	0.67	0.21
sealed area, i.e. building area (ALKIS class 41,001) and traffic area (ALKIS class 42,001)	0.10	0.79	0.38
Euclidean distance (m) to nearest forest patch >1 ha	13.8	2,785.6	609.6

Table 3. Characteristics of potential predictor variables, covariates, and their distribution in and around 103 private gardens in the Braunschweig region. Meteorological covariates observed at various times on or before the sampling day. Predictor variables were selected and aggregated according to Kiewra et al. [14].

				Cumulative number of hours with
Condition measured	Air temperature^1 (°C)	Relative humidity^1 (%)	Precipitation^2 (mm)	Air temperature >8°C	Air temperature >8°C + relative humidity >60%
on same day
minimum	6.0	53.5	0.0	7	1
maximum	21.9	83.5	6.3	24	23
median	13.7	65.4	0.0	23	11
2 days prior
minimum	6.2	59.0	0.0	21	2
maximum	22.1	88.9	15.9	48	48
median	13.0	68.1	0.2	46	28
7 days prior
minimum	4.3	58.3	0.0	28	8
maximum	23.6	80.5	24.1	168	152
median	12.9	69.3	9.6	155	86

¹measured at 2 m height; ² measured at 1 m height.

Figure 5. Proportion of transects with ticks present in the 103 sampled gardens.

Table 4. Distribution of questing Ixodes ricinus ticks on transects on which at least one tick was found, when sampling 2,666 transects in 103 private gardens in the Braunschweig region.

Number of questing ticks			Number of transects with at least one questing tick
Stage	Total	Maximum per transect
Nymphs	2,475	60	791
Males	334	16	217
Females	384	11	251
Total adults	718	27	371
Total ticks	3,193	62	956

Figure 6. Comparison of the effects of various vegetation types on the occurrence probability (a) and abundance (b) of questing Ixodes ricinus ticks in private gardens in the Braunschweig region. The letters above the boxes denote effects that differ significantly from all other effects with different letters.

Figure 7. Modeled occurrence probabilities of questing Ixodes ricinus ticks in private gardens in the Braunschweig region, characterized by the vegetation type on the sampled transects, related to varying proportions of forest in a 500 m buffer around the garden (left) or related to varying numbers of cumulative hours of air temperatures >8°C on sampling day (right). Shaded areas around the lines display the 95% confidence interval.

Table 5. Occurrence and abundance of questing nymphal and adult Ixodes ricinus ticks in 103 private gardens in the Braunschweig region in the final generalized linear mixed-effects models and their performance. Reference for comparisons was lawn as vegetation type (intercept), n = 2,666 transects.

Variables	Occurrence model				Abundance model
	Coefficient	SE	Significance^1	Odds ratio (95% CI)^2	Coefficient	SE	Significance	1 tick per x meter^3
Intercept	−1.52	0.16	***	0.22 (0.16–0.30)	−1.87	0.13	***	32.1
Vegetation type:
hedge	1.46	0.14	***	4.33 (3.32–5.65)	1.20	0.10	***	9.8
groundcover	0.87	0.17	***	2.40 (1.71–3.35)	0.77	0.12	***	15.0
no vegetation	0.77	0.23	***	2.17 (1.38–3.39)	0.99	0.16	***	12.1
flower/vegetable bed	0.19	0.14		1.21 (0.92–1.59)	0.11	0.11		29.2
Proportion of forest	0.73	0.12	***	1.07^4 (1.05–1.08)	0.59	0.10	***	NA^5
Hours >8°C on sampling day	−0.22	0.11	*	0.81 (0.65–0.99)	−0.21	0.08	*	NA
R^2 with fixed effects only			0.31		0.23
R^2 with fixed and random effects			0.68		0.67
ROC-AUC			0.83		-

¹Levels of significance: *** <0.001; ** <0.01; * <0.05; ² CI – Confidence interval; ³ Estimate analogous to odds ratio; ⁴ with each 10% increase; ⁵ NA – not applicable.

Figure 8. Modeled abundance of questing nymphal and adult Ixodes ricinus ticks on transects, characterized by the vegetation type, in private gardens in the Braunschweig region, related to varying proportions of forest in a 500 m buffer around the garden (left), or related to varying numbers of cumulative hours of air temperatures >8°C (right). Shaded areas around the lines display the 95% confidence interval.

Kiewra D, Kryza M, Szymanowski M. Influence of selected meteorological variables on the questing activity of Ixodes ricinus ticks in Lower Silesia, SW Poland. J Vector Ecol. 2014;39:138–145.

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