>About this Guide
>Table of Contents
1. What you can do
5. Environmental Issues
6. Keystone species
7. Get Wet!-
Field Study Ideas
8. The Zoo Experience
9. Frogs & Friends
10. Case Studies
CASE STUDY 2: THE DECLINE OF THE LEOPARD FROG(Level: 7 : 9 acad : 9 appl : 10 acad : 10 appl : 11 appl : 12 acad )
The Leopard Frog, Rana pipiens, easily recognized by its black leopard spots, was once distributed across North America. Wetlands from California to Northwest Territories hosted healthy populations of the species. Every spring, the warm shallow breeding ponds erupted in a chorus of chuckling Leopard Frogs. In some areas, the frogs were so abundant that they were commercially harvested for fish bait and student dissections. The bountiful harvest ceased in the 1960s, when the thriving chorus fell silent in wetlands across North America.
In Alberta, the Leopard Frog population began to decline in the mid 1970s. By 1990, only 32 sites across the province held a population of the frog. Even more alarming was the apparent lack of breeding. Successful reproduction was occurring at only five sites within the province. What has caused this baffling decline of the Leopard Frog? Although populations have fluctuated in the past, the present decline is too widespread to be considered a natural phenomenon.
The disappearance of amphibians such as the Leopard Frog coincides with the destruction of wetland habitats. Alterations to the critical breeding and overwintering sites can have a serious effect on an amphibian population. The Leopard Frog requires clear, clean water found at the edges of ponds or streams. Permanent water bodies which do not completely freeze in winter provide overwintering habitats. These habitats have been the target of human destruction in the past. Wetlands have been altered by pollution, or destroyed to provide land for agriculture, residential development, or transportation.
The destruction of wetland habitats can not explain the disappearance of the Leopard Frog in areas which have been protected from human exploitation. Acid rain, ultraviolet radiation, increases in pesticides, and the decade long drought may have contributed to the decline. The sensitive permeable skin of Leopard Frogs makes them especially vulnerable to pollution in the air and water. Predation by humans and other species may also limit the population. Perhaps a combination of these factors weakened the population until the inevitable crash.
There are several hurdles which are preventing the re-establishment of the Leopard Frog in Alberta. The population is extremely small which places it at a greater risk. Events which may appear to be insignificant can have a serious impact on the struggling population. Pesticide spills, water contamination by domestic animals, or drought can devastate a small population.
The distribution of the Leopard Frog within fragmented habitats is an additional barrier to the recovery of the Population. Leopard Frogs in isolated wetlands are unable to breed with other populations. In addition, the dry areas between the wetlands prevent the frogs from increasing their range. The isolated wetlands are essentially islands.
The recovery of the Leopard Frog began in Alberta in 1989 with a poster campaign. The poster encouraged the public to determine the distribution of the leopard frog across the province. Although it is difficult to manage the Leopard Frog without understanding the cause or causes of the decline, it is not impossible. It is crucial to conserve or rehabilitate existing wetland habitats, or create wetlands where none exist. Interference with ground water levels should be eliminated. Captive breeding programmes followed by re-introduction into key areas could encourage the recolonization of the Leopard Frog.
The current crisis facing the Leopard Frog in Alberta is one which is common to many species of amphibians throughout the world. Cyclic fluctuations in populations are normal, but worldwide disappearances are a cause for concern. The decline of the Leopard Frog may signal a deterioration of the environment which has been previously ignored.
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