Amphibian Conservation - Black Toad

Overview

The black toad is endemic to Deep Springs Valley, a mosaic of private, federal, and state land, nestled between the White and Inyo Mountain Ranges. Although two population studies indicate a stable population, the black toad has among the smallest range of any North American anuran which puts the species in a potentially precarious position, especially considering that its requisite aquatic habitat is surrounded by desert. A census performed in part of the range of the toad in 1978 estimated a population size of 7,897 to 9,744 toads. We surveyed this population in the same area in 1999 and estimated 8,419 toads. The black toad has dual California designations: Fully Protected and Threatened. The Fully Protected status actually diminishes the Department's ability to beneficially manage toad habitat, but innovative methods by us and our partners still allow for some habitat restoration.

The toad is highly aquatic, only leaving spring flow areas during migrations to other springs. The connectivity among springs and streams via desert washes is key to enabling this important meta-population behavior that retains the toad's genetic fitness.

Taxonomy

Research and Conservation Efforts

Deep Springs Valley is an arid desert habitat, punctuated by numerous springs, most located along scarps. These wet springs are critical to the toad's persistence. A native springsnail, Pygulopsis wongi, named after retired Bishop CDFW biologist Darrell Wong, is found in many of these springs. The below photograph shows one of the larger spring ponds with an outlet that flows towards Deep Springs Lake, in the background.

Management of the toad is integrally tied with grazing, as the main land owner and permittee is Deep Springs College, a private liberal arts school that is known for fostering a strong work ethic in its students. The College facilitates a Holistic Resource Management Team comprised of representatives from various agencies, occasional NGO representatives, and college staff and students. This team meets at least twice a year to review grazing schedules, inspect allotments, discuss management alternatives, and proposed beneficial projects, such as fencing exclosures to reduce grazing impacts, invasive species removal, et cetera. This poster (PDF) is one example depicting student and staff involvement with the toad.

CDFW biologists have worked with University Nevada, Reno; Deep Springs College, UC Davis, and other researchers. The citations below are some of the more recent literature about the toad, as well as the landmark Kagarise-Sherman study that resulted in new grazing management policies that have benefited the toad. Simandle's research showed that black toads exist as a metapopulation of at least three subpopulations. The four defining characteristics of metapopulation dynamics are: (1) that distinct breeding subpopulations exist, (2) that extinction and recolonization among subpopulations occur, (3) extinctions in subpopulations are primarily due to stochastic processes in otherwise suitable habitat, and (4) that there is limited dispersal among subpopulations. Both direct measures (mark-recapture, historical records, and observations) and indirect methods (i.e. genetic analyses) were used to evaluate the evidence for these four criteria. Eric's work informed the local CDFW office of the expectations that some subpopulations may demonstrate a natural extinction-recolonization dynamic, that unoccupied but suitable habitat must be conserved as it represents areas that may be recolonized in the future, and that activities that increase patch isolation, or decrease patch size are detrimental to the persistence of the metapopulation. Toad use has already been documented recently where previous surveys resulted in no toad observations.

Notes

1. Chytrid fungus, which is known to occur in amphibians, and may be implicated in their decline. To avoid spreading this disease, we are using equipment dedicated for use only on the black toad. Researchers must obtain a Scientific Collecting Permit from the Department to work with the toad, and local CDFW usually accompany them on sight. Of concern: cattle moving through different watersheds, then returning to the Valley. Currently, most waters on allotments have no known amphibian populations that would harbor chytrid and allow the cattle to act as vectors.
2. Increased grazing. As pressure to remove alpine grazing increases (see meadow photo), it is likely that more grazing will occur in the valley. The College is aware and sensitive of the toads' presence, but does not always believe that grazing is causing an impact -- especially since population estimates have remained constant over a twenty-year period. Efforts reduce cattle impact by keeping cattle away from breeding habitat from Mid March until June 1, when the majority of toads will have metamorphosed are in place at some of the breeding sites. A Holistic Resource Management Team made up of multiple agency and citizen representatives assists in the management of grazing activities.
3. Water. With climatic changes, geologic activity, and increased water use in the valley (wells, agricultural diversions for stock water and farming, and domestic use) groundwater levels and spring flow is a major concern.

Literature

• Population structure and conservation of two rare toad species (Bufo exsul and Bufo nelsoni) in the Great Basin, USA , Simandle (2006).
• Fine-scale population structure in a desert amphibian: landscape genetics of the black toad (Bufo exsul). Wang (2009).
• 2003 Population status and conservation of the black toad, Bufo exsul, Murphy (2003).
• A comparison of the natural history and mating system of two anurans: Yosemite toads (Bufo canorus) and black toads (Bufo exsul), Sherman (1980.