Science Story

Small variations in breeding pools make for big differences in Yosemite toad use

Paul Meznarich
Pacific Southwest Research Station
June 30th, 2017 at 12:00PM

The Yosemite toad (Anaxyrus canorus) is a rare species found exclusively in California’s Sierra Nevada. While its range encompasses hundreds of miles, spanning five national forests and two national parks, the livelihood and future survival of this federally threatened species may come down to mere centimeters.

A photo of a breeding pair of Yosemite toads
A breeding pair of Yosemite toads (Anaxyrus canorus); a rare species found exclusively in California’s Sierra Nevada mountain range. Christina Liang, USDA Forest Service.

According to research by the U.S. Forest Service’s Pacific Southwest Research Station and its collaborators, for pools within alpine meadows to be suitable habitat for laying eggs and sustaining tadpoles, little things mean a lot.

“Our research looked at pools across the toad’s range, in a variety of weather and precipitation conditions across a number of years,” said Christina Liang, a research ecologist with the Pacific Southwest Research Station and lead author of the study. “But no matter the year-to-year variations, we found relatively consistent and definitive characteristics were shared by the majority of pools supporting Yosemite toad offspring compared to those unoccupied.”

In Liang and her colleagues’ study, “Fine-Scale Habitat Characteristics Related to Occupancy of the Yosemite Toad,” they found the following differences, on average, between occupied and unoccupied pools:

  • Depth of bottom debris: 1.62 cm (occupied) versus 1.69 cm (unoccupied)
  • Pool vegetation height: 13.20 cm versus 14.16 cm
  • Water depth: 4.35 cm versus 3.65 cm
  • Water temperature: 24.82 degrees C (76.68 F) versus 21.75 degrees C (71.15 F)
  • Percentage of surface water along the pool’s width: 60.57 percent versus 40.07 percent

This new understanding of microsite suitability can provide land managers with valuable insights on how they can foster the species’ future survival.

“Understanding the complexity of toad breeding habitat is critical to the conservation of the species,” said Stephanie Barnes, an aquatic biologist on the Sierra National Forest. As land managers focus on watershed health to maintain clean and sustainable water supplies, creating suitable breeding habitat can be built into restoration plans.

“We want to create the right habitat for these toads wherever possible,” she said.