Why Are Some Animal Populations Unaffected Or Positively Affected by Roads?
Why are some animal populations unaffected or positively affected by roads?
Trina Rytwinski and Lenore Fahrig
Electronic Supplementary Material
Table S1. Definitions of the behavioural scenarios used in the six experiments and how roads and traffic were expected to impact population size/persistence for each. Traffic mortality = enhanced mortality due to collisions with vehicles; resource inaccessibility = less access to food, mates, habitat etc. (barrier effect); habitat loss = less habitat available for breeding, foraging etc.); population subdivision = populations become fragmented into smaller, partially isolated local populations that are more vulnerable to extinction.
Behavioural Responses / Definition / Expected road and traffic impacts1. road attraction + vehicle avoidance / Animal are attracted to a road for a resource (e.g., for food, a nesting site, a mate, or thermoregulation). Once on the road, animals can avoid oncoming vehicles, resulting in some individuals returning to the original side of the road and others crossing the road. / no negative road effects
increased resources
2. road attraction + no vehicle avoidance / Animal are attracted to a road for a resource (e.g., for food, a nesting site, a mate, or thermoregulation). Once on the road, animals cannot avoid oncoming vehicles. / traffic mortality
3. vehicle avoidance / Animals can avoid oncoming vehicles, resulting in some individuals returning to the original side of the road and others crossing the road. / no negative road effects
4. traffic disturbance avoidance / Animals avoid roads from a distance due to traffic disturbance (e.g., lights, noise, chemical emissions). / resource inaccessibility habitat loss
population subdivision
5. road surface avoidance / Animals avoid going onto the road surface itself. / resource inaccessibility population subdivision
6. no avoidance / Animals move onto roads irrespective of traffic. / traffic mortality
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Why are some animal populations unaffected or positively affected by roads?
Trina Rytwinski and Lenore Fahrig
Figure S1. Illustration of traffic disturbance avoidance, T, road surface avoidance, R, road attraction A, vehicle avoidance C and the probability of animals killed on the road, M.
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Why are some animal populations unaffected or positively affected by roads?
Trina Rytwinski and Lenore Fahrig
(a)
(b)
Figure S2. a) Probability of an animal avoiding the road from a distance, as a function of traffic density V (held constant at 3 for the current runs). Probability of traffic disturbance avoidance was estimated by the avoidance parameter k (note: probability of vehicle avoidance was estimated by the same avoidance parameter k); b) Probability of being killed on a road for a given animal, as a function of traffic density. Probability of traffic mortality was estimated by varying the mortality parameter d. In the current runs, k was either 0 or 200, corresponding to 0% and 100% probabilities (respectively) and d was either 0 or 2.5, corresponding to 0% and 88% probabilities (respectively).
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Why are some animal populations unaffected or positively affected by roads?
Trina Rytwinski and Lenore Fahrig
Figure S3. Illustration of a traffic disturbance zone. Animals that avoid traffic disturbance due to vehicle lights, emissions, noise or pollution, avoid the habitat near roads from a certain distance away from the road(s). In the current simulations we assumed that the large-bodied species avoided the roads from 45 grid cells away (450m) and the small-bodied species type avoided the roads from 1 grid cell away (10m).
References
Jaeger JAG, Fahrig L (2004) Effects of road fencing on population persistence. Conserv Biol 18:165-1657
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