Skip navigation Wilderness: Roads to Ruin?


1. Road rage

2. Pavement or depravement?

3. Spreading like weeds

4. Amphibian perambulations

5. Down the corridor









Juvenile spotted salamanders, a forest-dweller of eastern North America, stuck to the forested side of this experimental setup. Photo: Courtesy Betsie Rothermel, University of Missouri.








According to new research, amphibians may get dangerously dry while crossing a road.


  Road barriers
yellow spotted salamander on a starWhere an ATV rider might see a forest road as a road to bliss, an amphibian -- say a toad or a salamander -- might see it as a barrier. Amphibs actually face twin road hazards: they can get squashed on roads located near their wetland homes.

Or they can avoid crossing roads, and thus lose access to essential habitat.

The second hazard can be as deadly as the first, because amphibians by definition need both wet and dry habitat. Salamander larvae -- tadpoles to you and me -- develop in water, and then migrate to dry land, where they metamorphose into salamanders.

After metamorphosis, the juveniles are susceptible to water loss, says Raymond Semlitsch, a professor of biology and ambitious amphibianist at the University of Missouri. "Unlike birds, mammals or reptiles, which have protection against water loss, amphibians are like a sponge -- if you put a wet sponge out in the dry summer, it will dry up. They are limited in how far they can move, and under what conditions they can move."

Two S-shaped salamanders  curve around each other.

Now that landscapes are chopped up by roads, houses and farm fields, the ability to survive dry conditions becomes a "key question in terms of dispersal, and how they deal with highly disturbed landscapes," Semlitsch says.

And dispersal is key for amphibians, which tend to die out in any specific locale over the years. If other amphibs cannot disperse back to those locations, the population will eventually shrink and perhaps disappear.

On the toad road
In a series of studies, Semlitsch and colleagues looked at how salamanders and toads deal with habitats like the roads confronting migrating amphibians (see "An Experimental Investigation..." in the bibliography). In one experiment, they put toad and salamander larvae in a pool at the border between a forest and an old field, and recorded their movement as they metamorphosed and migrated toward the drier habitat needed by adult toads and salamanders.

A fat toad sits on the ground. A juvenile American toad, a widespread species that lives in varied habitats in eastern North America. Courtesy Betsie Rothermel, University of Missouri.

The researchers measured how fast the animals traveled, how well they survived in each habitat, and whether they started truckin' toward the field or forest in the first place.

Some of the results were surprising. The American toad, for example, is not considered choosy about habitat, at least as an adult, but the toad juveniles preferred the forest to the field. Why? Perhaps, Semlitsch says, because they are so small that they could get parched in the old field.

The right road
Other results were more predictable, Semlitsch adds. The spotted salamander, a forest species, did prefer forest, while the small-mouth salamander, a prairie species, had no habitat preference.

In a different study, the results on adult spotted salamanders were more dramatic. When Semlitsch and colleagues implanted radio transmitters into the amphibians, 98 percent chose forest, not field, for their wanderings. After two years, all the spotted sallys confined in the field had croaked, while about 25 percent survived in the forest.

Pool of water at line dividing field from forest.
Here's the experimental setup. The amphibians were dumped in the pool at center, and then they chose whether to migrate toward forest or old farm field. Courtesy Betsie Rothermel/Raymond Semlitsch

Beyond issues of forest fragmentation, the new data should contribute to solving the global question of amphibian decline, Semlitsch indicates. Because amphib numbers in each specific location naturally fluctuate, "It comes down to the fact that local population extinction, which could lead to species extinction, is really a function of how well amphibians persist in the landscape, and that's a very direct function of dispersal, of moving from disturbed areas that are low-quality, to a site that is high-quality."

In other words, if you can't roll with the punches, you face a knockout.

Can these "roads" actually help species survival?

The Why Files

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