Showing posts with label roads. Show all posts
Showing posts with label roads. Show all posts

Wednesday, April 4, 2012

More on Roads as Barriers to Wildlife

Psammodromus algirus a forest species that does not appear to cross roads. 
Photo Credit: Mario M.
Roads, railways, fences and other linear structures may act as barriers to dispersal of a variety of species. The long term effects may be to interrupted gene flow between populations, but the impact of linear structures may differ for species. In a recent study Telleria et al (2011) examined the effect of a 25 year old motorway on the distribution of several forest species in a fragmented landscape in northern Spain. The patches of forest in the study area are becoming scarcer and increasingly fragmented to the west. The highway runs perpendicular to the westernmost tips of the fragmented area, isolating forest patches from eastern habitat patches. These eastern habitat patches are better connected to large forests located further east in the ‘Sierra de la Demanda’ mountain range, and might act as source habitats. When the motorway was constructed populations of forest vertebrates were expanding westwards from these mountains as a consequence of human abandonment of the low productivity highlands. A barrier effect might therefore have caused asymmetric population dynamics on either side of the motorway, obstructing the recovery of local extinctions in western forest patches by individuals moving from mountain forests. The researchers aim was to look for evidence of a barrier effect . They found clear evidence of a barrier effects on the distribution of the forest lizard Psammodromus algirus.The roe deer (Capreolus capreolus) was also unequally distributed on both sides of the motorway, but this may also be due, at least in part, to fragmentation. The eyed lizard (Timon lepidus),a species that can move through open fields, showed no evidence of barrier effects. The distribution of two small birds (Erithacus rubecula and Phylloscopus bonelli) was unaffected by the road. Their results demonstrate roads may severely restrict the distribution of species which can withstand high levels of forest fragmentation but have limited dispersal ability.

Citation
Tellería JL., Díaz JA, Pérez–Tris J, De Juana E, De la Hera I, Iraeta P, Salvador A, Santos T. 2011. Barrier effects on vertebrate distribution caused by a motorway crossing through fragmented forest landscape Animal Biodiversity and Conservation 34: 331-340.

Monday, August 8, 2011

Snakes & Traffic

Roads have long been thought detrimental to snake populations, while at the same time roads provide insight into what species may be present in a given area. Two studies done in quite different part of the world and habitats suggest heavy traffic is damaging snake populations.
Black-tailed Rattlesnake, Crotalus molossus. JCM
Recently published results from a 27 year study (Jones et al., 2011) surveyed snake communities at two locations in the Sonoran Desert in south central Arizona. Both the Lower Colorado River Valley subdivision community south of Phoenix and the Arizona Upland subdivision community west of Phoenix were found similar in diversity and abundance with four species (Crotalus cerastes, C. atrox, C. scutulatus, and Rhinocheilus lecontei) accounting for 67–70% of all individuals at the two sites. The study consisted of 50 road-riding surveys yielding 175 snakes in 2,538 km (0.069 snakes per km) in the Lower Colorado River area and 80 road surveys in Upland areas west of Phoenix surveys, yielding 397 snakes in 6,391km (0.062 snakes per km) of roads. Of interest is the decline in snake numbers with dramatic increases in roadway traffic volume. The increase in traffic volumes from ~ 500 vehicles per day to over 3,000 vehicles per day at both of our sites was coincident with a decline in snakes found alive on the road, a finding quite similar to results obtained in a similar study of surveying for amphibians in North Carolina in relation to traffic volume. The amphibian study found almost twenty times as many amphibians were found on roads with less than 550 vehicles per day than with more than 2,000 vehicles per day.

In a second study done in Brazilian rainforest, over a shorter period of time Hartman et al (2011) sampled a 16 km tract of a paved road from October, 2001 to December, 2002, totaling 5,173 km. The most commonly found species were Chironius exoletus, C. bicarinatus, Oxyrhopus clathratus, and Chironius fuscus. They found 60 road killed snakes (0.0115 snakes per km), belonging to 15 species, representing about 58% of the species recorded for the region. Hartman et al. suggest the more mobile species seemed are more vulnerable to road mortality than sedentary species because species encountered dead on the road tended to be active foragers and show plasticity in microhabitat use. The high number of juveniles found in May could reflect juvenile recruitment. The increased road mortality in October may result from males searching females during the mating period.

Literature

Hartmann, P. A. et al. 2011. Snake Road Mortality in a Protected Area in the Atlantic Forest of Southeastern Brazil. South American Journal of Herpetology 6(1):35-42.

Jones, T. R. et al. 2011. Sonoran desert snake communities at two sites: concordance and effects of increased road traffic. Herpetological Conservation and Biology 6:61-71.