Roads Flashcards
The impacts of roads on biodiversity
Drivers of rainforest loss
Proportion of drivers may change across the globe but all activities are facilitated by roads
- subsistence agriculture
- logging
- intensive agriculture
- ranching/pasture
Roads facilitate economic and social development
Market access for timber & agricultural products
Access to remote areas
Lower costs of land clearing
Cheap labour
Ecological effects of roads
Habitat loss
Road mortality
Edge effects
Barrier effects and fragmentation
- Habitat loss
Habitat loss is the initial and most obvious impact of roads/powerlines
Road/powerline networks may alter or destroy scarce natural habitats
Facilitate further clearings
In brazisial amazonia
Road network doubled: 87,000 to 161,500 km
> 95% Amazonian deforestation within 50 km of a road (Laurance et al. 2009 TREE)
Adeney et al.
Reserves protect against deforestation fires in the amazon
12 fires 10km from road vs. 3 fires 10km from road
1 fire 50km from road vs. no fire 50km from road
- Road mortality
Significant population sink (sources/sinks & cassowaries)
Features of susceptible wildlife: slow-moving, arboreal, terrestrial or flying, nocturnal or crepuscular
Road mortality
Species attracted to roads/roadsides such as amphibians, reptiles, herbivores & frugivores, carrion feeders & predators
Species with nearby habitat – wetlands, grassy verges, fruit
Species with large-area requirements
Road mortality
Road features that increase mortality rates: width, traffic speed & volume, roadside vegetation & adjacent habitat
Significant population sinks can occur for rare and endangered species
Brown and Brown, 2013
An estimated 80 million birds are killed by colliding with vehicles on U. S. roads each year [1], and millions more die annually in Europe [2] and elsewhere. Losses to vehicles are a serious problem for which various changes in roadway design and maintenance have been proposed [3]. Yet, given the magnitude of the mortality reported for some species [4], we might expect natural selection to favor individuals that either learn to avoid cars or that have other traits making them less likely to collide with vehicles.
If so, the frequency of road kill should decline over time. No information is available for any species on whether the extent of road-associated mortality has changed [2]. During a 30-year study on social behavior and coloniality of cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska, we found that the frequency of road-killed swallows declined sharply over the 30 years following the birds’ occupancy of roadside nesting sites and that birds killed on roads had longer wings than the population at large.
Road mortality impacts on different taxa
Amphibians suffer greater losses
Increased road width causes declines in mortality
Road-related mortality –
bush meat hunting
- Edge effects
Cut and fill
construction
Impeded water flows
Edge effects - pollution
Chemical emissions may lead to pollution of air, soil and water adjacent to roads
Energy emissions in the form of noise, headlights, vibrations & movements may disturb sensitive wildlife
Edge effects – habitat decay
Changing microclimatic conditions –humidity, light, temperature; wind speed & turbulence
Increased tree damage and death
Increased tree dynamics - turnover, species composition
Changes in stream ecology - altered flow patterns impacts on aquatic & stream bank life
Edge effects - wildlife
Ware et al., 2015 Phantom road experiments reveals traffic noise is an invisible source of habitat degradation 31% of birds avoided the ‘road’
Birds that stayed had lower overall body condition (mass/length)
Laboratory experiments suggest vigilance-foraging behaviour tradeoff as a mechanism
Do all species suffer from roads?
Laurance et al. 2004 Conserv Biol
Edge avoidance by understory birds
Vs. edge loving by gap & canopy spp
- Barrier effects of linear clearings
Divide up habitats & wildlife populations?
Roads can be barriers to gene flow
genetic differentiation among populations?
Smaller partially isolated populations at greater risk of extinction due to deterministic processes
limiting a critical resource (food, shelter or space)
Random demographic changes
Random environmental changes
Barrier effects
Features that influence the permeability of linear clearings
Clearing characteristics - width, traffic volume & speed, adjacent vegetation, road cuttings
Species characteristics – behaviour, mobility, habitat specificity (generalist vs specialist)
Bird movement responses to roads?
Passive obs:
- birds cross
- birds do not cross
Experimental translocations:
- Birds can cross when forced (local mvmts disrupted)
- Birds do not cross (dispersal disrupted)
Observation: Road avoidance
Implications
Dispersal is a principle factor determining wildlife survival
Populations could become isolated by roads
Experimental translocations
Highway clearing
50 – 75 m wide
MSF Rapid return 3-19 hrs Understory 24-48 hrs Terrestrial No return 24-48 hrs
Mitigation methods
AIM: To increase permeability of roads
1) Decrease road widths, allow regrowth and canopy connections (but more road kill)
2) Extend bridges over watercourses to include terrestrial vegetation
3) Reduce road speeds (windy roads better) in protected areas
4) Prohibit hunting (but can it be enforced?)
Mitigation methods-road signs
Do they work?
Do people actually slow down?
Mitigation methods-road closures
Only on small roads
Economic incentive to protect species?
