CHAPTER 1 INTRODUCTION
5. FAUNA
3.2 The effects of biophysical factors on the occurrence of roadkill on paved and unpaved roads
3.2.1 Season
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3.2 The effects of biophysical factors on the occurrence of roadkill on paved
101 3.2.2 Rainfall
Rainfall is ordinarily a continuous variable but in this analysis, it was categorised into days in which rain had fallen in the preceding 24 hours and days when no rain had fallen in the preceding 24 hours. A t-test was used to assess the difference between the number of roadkill detected per day on days when no rainfall had fallen and when it had rained in the preceding 24 hours. Rainfall was selected as a categorical variable due to the poor rains experienced in the region during the study, and was therefore erratic. The highest rainfall occurred during the hot/dry season (28.6 mm), with 18.5 mm during the hot/wet season. No rain fell during the cold/dry season.
Rain in the preceding 24 hours had a significant effect on roadkill on the paved roads, with more roadkill observed per day when rain had fallen 24 hours prior to the assessment than when it had not (t118 = -3.4, p <0.05; Figure 4.14a). There was no significant effect of rain in the preceding 24 hours on the unpaved road (t4 = -0.32118, p = -0.75; Figure 4.14b).
No rain Rain
Rainfall -10
-5 0 5 10 15 20 25 30 35
Number of roadkill detected per day
No rain Rain
Rainfall -1.5
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Number of roadkill detected per day
Figure 4.14: The difference between the number of roadkill detected per day on days when no rainfall had fallen in the preceding 24 hours, and days when rainfall had not fallen (± 95% CI) along (a) a 100 km section of paved road and (b) a 20 km section of unpaved road in the GMTFCA, South Africa.
(a)
(b)
102 3.2.3 Moon phase
Moon phase had no significant effect on the number of roadkill detected per day on the paved road (one way ANOVA; F7,112 = 1.6, p = 0.98 ; Figure 4.15a) or on the unpaved road (one way ANOVA; F7,15 = 0.3, p = 0.96; Figure 4.15b).
New moon
Waxing crescentFirst quarter
Full moonWaning gibbous
Last quarterWaning crescent
Waxing gibbous Moon phase
-2 0 2 4 6 8 10 12 14 16 18 20 22 24
Number of roadkill detected per day
New moon
Waxing crescent First quarter
Full moon
Waning gibbous Last quarter
Waning crescent
Waxing gibbous Moon phase
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Number of roadkill detected per day
Figure 4.15: The difference between the number of roadkill detected per day and moon phase (data are means ± 95% CI) along (a) a 100 km section of paved road and (b) a 20 km section of unpaved road in the GMTFCA, South Africa.
(a)
(b)
103 3.2.4 Cloud cover
There was no significant effect of cloud cover on the number of roadkill detected per day on either the paved (one way ANOVA; F8,111 = 1.84; p = 0.8; Figure 4.16a) or unpaved roads (one way ANOVA; F8,14 = 0.67; p = 0.7; Figure 4.16b).
0 1 2 3 4 5 6 7 8
Cloud cover
-2 0 2 4 6 8 10 12 14 16 18
Number of roadkill detected per day
0 1 2 3 4 5 6 7 8
Cloud cover
-2 -1 0 1 2 3 4 5 6
Number of roadkill detected per day
Figure 4.16: The difference between the number of roadkill detected per day and cloud cover (data are means ± 95% CI) along (a) a 100 km section of paved road and (b) a 20 km section of unpaved road in the GMTFCA, South Africa.
(a)
(b)
104 3.2.5 Humidity
A simple regression was used to examine the relationship between humidity and the number of daily roadkill. There was no significant relationship between humidity and roadkill detected per day on the paved road (adjusted R2 = -0.007; F1,118 = 0.86; p = 0.77; Figure 4.17a) or on the unpaved road (adjusted R2 = -0.0077; F1,21 = 0.09; p = 0.77; Figure 4.17b). While the linear relationships between the variables were significant, the low r2 indicates that the data points are scattered away from the best- fit line and that the independent variable was a poor predictor of the dependent variable.
10 20 30 40 50 60 70 80
Humidity (%) -5
0 5 10 15 20 25 30 35 40
Number of roadkill detected per day
20 25 30 35 40 45 50 55
Humidity % 0.5
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Number of roadkill detected per day
Figure 4.17: The relationship between the number of roadkill detected per day and humidity along (a) a 100 km section of paved road and (b) a 20 km section of unpaved road in the GMTFCA, South Africa, (dashed line = 95% CI).
(a)
(b)
105 3.2.6 Minimum temperature
A simple regression was used to examine the relationship between minimum temperature and the number of daily roadkill. There was a significant relationship between minimum temperature and roadkill on the paved road (adjusted R2 = 0.16;
F1,118 = 23.79; p <0.05; Figure 4.18a) with more roadkill detected per day as the temperature increased. There was no significant relationship between minimum temperature and roadkill on the unpaved road (adjusted R2 = -0.03; F1,21 = 0.59; p = 0.29; Figure 4.18b).
2 4 6 8 10 12 14 16 18 20 22 24 26
Minimum temperature (°C) -5
0 5 10 15 20 25 30 35 40
Number of roadkill detected per day
4 6 8 10 12 14 16 18 20 22 24 26
Minimum temperature (°C) 0.5
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Number of roadkill detected per day
Figure 4.18: The relationship between the number of roadkill detected per day and minimum temperature (data are means ± 95% CI) along a (a) 100 km section of paved road and (b) 20 km section of unpaved road in the GMTFCA, South Africa, (dashed line = 95% CI).
(a)
(b)
106 3.2.7 Maximum temperature
A simple regression was used to examine the relationship between maximum temperature and the number of daily roadkill. There was also a significant relationship between maximum temperature and roadkill on the paved road (adjusted R2 = 0.09; F1,118 = 12.89; p <0.05; Figure 4.19a) with more roadkill detected per day when temperature increased (Figure 4.19a). There was no significant relationship between maximum temperature and roadkill on the unpaved road (adjusted R2 = - 0.02; F1,21 = 0.47; p = 0.49; Figure 4.19b).
15 20 25 30 35 40 45 50
Maximum temperature (°C) -5
0 5 10 15 20 25 30 35 40
Number of roadkill detected per day
20 22 24 26 28 30 32 34 36 38 40 42 44 46
Maximum temperature (°C) 0.5
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Number of roadkill detected per day
Figure 4.19: The relationship between the number of roadkill detected per day and maximum temperature (data are means ± 95% CI) along a (a) 100 km section of paved road and (b) 20 km section of unpaved road in the GMTFCA, South Africa, (dashed line = 95% CI).
(a)
(b)
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3.3 The effect of environmental factors on the occurrence of roadkill on