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Columbia Spotted Frog

Limiting Factors

Illustration of the Columbia Spotted FrogLimiting factors are conditions that adversely affect the ability of a species to reproduce, disperse or survive. For the Spotted Frog, natural limiting factors such as slow developmental rate, overwintering mortality and predation may further limit the ability of populations to recover if disturbed. The following section stresses human-caused disturbance factors that may negatively affect the population growth and distribution of Spotted Frogs and includes Predation by introduced species, Habitat Loss, Changes in Water Quality, Disturbance, Competition, and Global Climate Changes.

Predation by Introduced Species:  The introduction of predatory fish into previously fish-free water bodies has contributed to the decline of amphibians in several areas of western North America. The introduction of Rainbow Trout may have impacted the reproductive capacity of amphibians, including Spotted Frogs, in at least one wetland complex in Peter Lougheed Provincial Park

Habitat Loss:  Direct loss of habitat reduces the potential for survival and reproduction of Spotted Frogs. Valleys within the montane ecoregion are generally the most heavily impacted areas within the Rocky Mountains of Alberta. Unfortunately, significant populations of Spotted Frogs occur within these valleys. In Banff and Jasper National Parks, breeding sites were lost when ditching drained breeding ponds on the east side of the Banff-Jasper Highway. There is a high probability that areas such as the Bow Corridor, the Kananaskis Valley, and the Waterton/Crowsnest region have also experienced losses and alterations of Spotted Frog habitat.

Urbanization and development may also become an increasingly important aspect of habitat loss for Spotted Frog populations in Alberta. Due to the considerable amount of planned development in the Westcastle area, Spotted Frog habitat is currently under threat by road construction and recreational developments. The rapid pace of urbanization in the lower mainland region of British Columbia, in combination with the introduction of non-native amphibian species, may have already caused the extirpation of Rana pretiosa from Canada.

Habitat loss and degradation due to wetland drainage, livestock grazing and forestry practices may also impact Alberta populations of Spotted Frogs. In British Columbia, the increasing loss of wetland habitats as a result of human activities, as well as the continued disruption and landscape-level changes associated with large-scale logging practices are of particular concern for the Columbia Spotted Frog.

Changes in Water Quality:  High concentrations of soluble salts in water occupied by Spotted Frogs may hinder spring emergence and larval development. Pollution might have detrimental effects on Spotted Frog populations within Banff and Jasper National Parks. Minimal salting of the highways near Spotted Frog habitat is recommended.

Disturbance:  One of the causes of mortality of Spotted Frogs was direct human activity. In Yellowstone National Park individual frogs were found run over by vehicles, trampled by foot traffic, killed by children and used for fish bait. Comparable problems may also impact Spotted Frog populations in similar situations throughout the mountains.

Competition:  Spotted Frogs are being negatively affected by Northern Leopard Frogs and the introduction of Bullfrogs (Rana catesbeiana) in some areas. The protracted period required for sexual maturity in Spotted Frogs (4 to 6 years) may leave it more vulnerable to disturbance and competition from more aggressive, faster growing introduced species. 

Global Climate Changes:  Increased concern has been expressed for the susceptibility of amphibians to the effects of increasing levels of ultra-violet radiation (UV-B) at mid- and high latitudes. The life history of Spotted Frogs may render this species particularly vulnerable as they have floating egg masses, occupy high elevation habitats, and breed early in the year when UV-B levels are high.

Reprinted from Alberta Wildlife Status Report No. 17 (1998), with permission from Alberta Sustainable Resource Development.

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