Great Basin spadefoot (Spea intermontana) COSEWIC assessment and status report: chapter 11
Technical Summary
Spea intermontana
Great Basin Spadefoot – Crapaud du Grand Bassin
Extent and Area Information
The range consists of several separate regions in the Okanagan valley Similkameen valley, Kettle-Granby River valley, Thompson-Nicola valley and South Cariboo, respectively. Populations in the Nicola Valley and in the South Cariboo might be further separated from the rest of the northern population. Calculated from distribution records from 1985 to 2006.
Method A) Calculated as the area of all observations from 1985 to 2006 buffered by a 1 km radius circle centred on each observation; overlapping circles were merged together to avoid counting the same area more than once. Method B) Calculated as the area of the 2 km × 2 km grid squares intersecting all observations from 1985 to 2006.
Calculated from distribution records from 1985 to 2006; localities closer than 500 m were considered the same site, and each distribution record was treated equally.
The increase in number of known sites within past 10 years due to increased search effort does not reflect an expansion of AO; it is unknown whether all sites recorded since 1985 are still occupied:
The number of occupied breeding sites fluctuates greatly from year to year, depending on environmental conditions, mainly availability of water:
Population Information
No data available – approximated from sexual maturity, which occurs at 2-3 years, and longevity (10 or more years):
based on observations of a few, very large choruses although numbers fluctuate from year to year and most choruses are small.:
List populations with number of mature individuals in each:
Threats (actual or imminent threats to populations or habitats)
- Loss of aquatic breeding sites as a result of human activities (housing developments; agriculture)
- Degradation of the quality of breeding habitat (altered hydrology, pesticides and other pollutants, intensive use by livestock)
- Fragmentation of habitat and road mortality.
- Disease, including chytridiomycosis
- Introduced species, including bullfrogs and predatory fish
- Loss and degradation of terrestrial foraging habitat and hibernation sites (housing, viticulture, soil compaction by cattle trampling)
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
Quantitative Analysis
- Not enough information
- NA
Current Status
- COSEWIC: Threatened (2001, 2007)
- BC: Blue list, S3
- NatureServe: N3
Status and Reasons for Designation
Status: Threatened
Alpha-numeric code: B2ab(ii,iii)c(iv)
Reasons for Designation: This small, rotund, toad-like amphibian has under each hind foot a prominent tubercle, or “spade”, which it uses for burrowing. The species has a restricted distribution in Canada in the semi-arid and arid areas of southern interior British Columbia. Parts of this region are experiencing rapid loss and alteration of critical habitats for the spadefoot, including loss of breeding sites, because of urban and suburban expansion, increased agriculture and viticulture, and the introduction of alien fish species and disease. The protected areas it inhabits are losing surrounding natural buffer habitats due to encroaching agricultural and housing developments. In consequence, available habitat in some parts of the range is becoming fragmented, resulting in increased local extinction probabilities for the sites that remain. Although spadefoots may use artificial habitats for breeding, there is evidence that such habitats may be ecological traps from which there may be little or no recruitment.
Applicability of Criteria
Criterion A: (Declining Total Population): Insufficient data to quantify decline.
Criterion B: (Small Distribution, and Decline or Fluctuation): Qualifies for Threatened as the Area of Occupancy is <1,000 km² and declines are evident in Area of Occupancy and in the area, extent and quality of habitat. The species is critically dependent upon a limited number of small breeding sites that are increasingly isolated from each other due to habitat fragmentation. Furthermore, there is a high probability of large fluctuations in the number of adult individuals.
Criterion C: (Small Total Population Size and Decline): May meet the criteria for Threatened C2a as the total adult population size may fluctuate below 10,000 individuals and overall decline in abundance may be inferred from the loss and degradation of habitats. Accurate estimations of decline in abundance are likely precluded due to fluctuating population sizes.
Criterion D: (Very Small Population or Restricted Distribution): Not applicable.
Criterion E: (Quantitative Analysis): Not applicable.