Skip navigation 'No Vacancy': family of snails approaches house with no vacancy sign out front

  Related Why Files
Snail sex

Plant diversity in trouble.

Earthworms attack.







The Niagara Escarpment is the steep face of a 650-foot bedrock ridge that runs from the northeastern United States across southeastern Canada, and then southward to southeastern Wisconsin. The portion in Ontario has been tagged as a World Biosphere Reserve by UNESCO. Photo: Wisconsin Department of Natural Resources.





























Tiny land snails like these often prefer to live on limestone outcrops like the cliffs along the Niagara Escarpment. Though diminutive, the creatures are an essential part of healthy cliff ecosystems. Original image © Jeffrey Nekola










The inconspicuous moss and lichens that spring from cliff-sides can be rare and delicate, and often much older than they appear. For this reason, even slight injury to a cliff can take years to repair. Photo: Wisconsin Department of Natural Resources.





The very ledges and nooks that make for great grabbing are also prime living quarters for a cliff's smaller inhabitants.

Original photo (above) from Government of South Australia.

  classified ad states: Wanted for rent: Nice gastropod family of eight seeks spacious cliff-side apartment. Preferably dark and moist with plenty of soil. Non-recreational location a must. Finding quality real estate is never easy, but for snails it can be especially tricky. Some cliff-dwelling species may be facing new shortages thanks to a popular -- and seemingly eco-friendly -- sport.

"The makeup of snail species changes dramatically along rock-climbed routes," says Jeffrey Nekola, an ecologist at the University of Wisconsin, Green Bay, co-author of a recent paper (see bibliography) detailing how climbers affect snail populations inhabiting the limestone cliffs of Ontario. More climbers means fewer snails, and Nekola believes some species may be at risk of serious decline or replacement by more aggressive varieties.

The new study is part of a bigger investigation of the flora and fauna that thrive on the crags of the Niagara Escarpment -- a 700-kilometer geological feature that arches from Wisconsin upwards through Ontario, and down into New York.

Map of Niagara Escarpment shows arch from Wisconsin to New York.

More than just a pretty face
To those who think of cliffs as mere edges of other ecosystems, think again. Cliffs haven't been granted the stardom of forests or wetlands, says Nekola, because for a long time people assumed they were probably as barren as they looked.

"When you have one of the seminal works in plant ecology saying 'well, these aren't real plant communities,' you know cliffs have not been seen as real habitats," Nekola says. "Part of it is that when you project that surface onto a horizontal plane, it doesn't exist."

But looks can bamboozle. Contrary to appearances, deserts, grasslands, and yes -- cliffs -- are home to rich communities of plants and animals.

grey bod, brown, striped shell: snail on green leaf. Text reads:Large species like Euglandina rosea, a native of the southern United States, may be what come 
to mind when you think snail. But cliff-dwelling varieties tend to be much smaller -- and harder to spot. Original photo: USGS

Cliff research has logistical obstacles, too, because vertical spaces often serve as property boundaries and have no discernible owner. But in the past decade, a growing body of research suggests there is an "incredible diversity and interesting assemblage of organisms" on the faces and inside of cliffs, Nekola says.

These include rare clusters of algae and fungi formerly thought to exist only in Antarctica, and a variety of goldenrod that grows nowhere else. And a breathtaking assortment of snails -- many rare or endangered -- dwell among the limestone ledges of southern Ontario. The limestone provides calcareous building material for shell construction, and the cracks provide protection from predators and the elements.

"In an area the size of a saucer, you can have upwards of 20 species coexisting," says Nekola. That's more than half the number of species of land snails in the average U.S. state.

Many are small as a 1/4-karat diamond and -- if you ask Nekola -- just as precious. "What's amazing about these organisms is that a great majority of their diversity is found within a few sites....Cliffs are certainly the richest of those."

A dozen tiny snails fit easily on a penny.

Cliff demographics
But of course, snails aren't alone on the rocky slopes. Aim a pair of binoculars at a swath of cliff on any sunny day and you'll no doubt spot a few Homo sapiens dangling around. With more than four million participants now in North America, rock climbing has steadily surged in popularity for half a century. The sport is touted as having a low environmental impact, and participants are often of the leave-no-trace ilk. So what's the problem?

Small green plants sprout from rocky edge.It appears that the very ledges and cubbyholes that make for great grabbing are also prime living quarters for a cliff's smaller tenants. Snails need moisture to move and secluded spaces to lay eggs. And despite their protective shells, many species are notoriously fragile. When a boot reaches deep into a nook for firmer footing, some of the soil inside is inevitably shed when the climber takes it out again. And local residents are likely evicted in the process.

Nekola and his colleagues knew from their previous work that plants and lichens growing on the Escarpment are less common in popular climbing spots than in unclimbed areas. This time, they compared the snails in soil samples taken from climbed and unclimbed areas. The snails, too, are sensitive to intruding fingers and toes.

Samples from climbed areas contained fewer than one-fifth the number of snails than were found in soil samples taken from unclimbed spots. And half of the 40 snail species identified in the unclimbed areas were completely absent from the samples taken from climbing routes.

"We found that snails documented to be tolerant of human activity had become the dominant species along [climbed] routes," Nekola says.

Watch your fingers
A ponytailed man clings to the side of a rust-colored cliff. Starting to wonder whether there's any way to enjoy nature without abusing it? Here's the good news: There is plenty of room for the peaceful coexistence of rock climbers and snails.

Watch where you grab -- cliffs like these support ancient forest ecosystems. ©Thor Backus

Recreational climbers and park managers should treat vertical trails with the same degree of care as horizontal trails, Nekola says. Some parks allow climbers to choose from unlimited possible avenues up a rock face, potentially ravaging entire cliffs. Instead, parks could designate limited routes that allow climbers to enjoy the best views and surest footing while leaving plenty of space for snails and other soil invertebrates to thrive.

Disturbed cliffs can take centuries to recover -- much like the delicate, slow-growing communities in alpine areas. "What we need to do is have a lot of humility when we decide we want to climb up a cliff," Nekola says. "If we're going on a virgin route, we're going to do so at the price of a lot of biodiversity. Is it worth it?"

-- Sarah Goforthsmall snail looks at author's name


McMillan, M., Nekola, J., Larson, D. 2003. Effects of Rock Climbing on the Land Snail Community of the Niagara Escarpment in Southern Ontario, Canada. Conservation Biology 17 (April): 616-621. Abstract available online.

Larson, D. W., U. Matthes, and P. E. Kelly. 1999. Cliffs as Natural Refuges. American Scientist Vol. 87: 5.


Credits | Feedback | Search

©2003, University of Wisconsin, Board of Regents.