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   Amphibian Biomonitoring Creating the Context: Background     
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INTRODUCTION

Over the last 50 years, many species of amphibians (frogs, toads, salamanders and newts) throughout the world have declined markedly in numbers. Some species have become extinct. In many cases the declines are a direct response to the impact of human activities (such as habitat destruction or pollution) acting at a local level. However, towards the late 1980s, biologists from many parts of the world reported declines in amphibian populations in apparently pristine habitats, such as national parks and nature reserves, where local effects could not be implicated. This led to the suggestion that there may be one or more global factors that are adversely affecting amphibians.

What are Amphibian Declines and their Causes?

Possible candidates for the causes of these declines are:

  1. An increase in ionizing radiation (UV-B) resulting from ozone layer depletion.
  2. Chemical contamination: the oestrogenic effects of pesticides, acid precipitation, or the effects of fertilizers and herbicides. For more information, visit the Herptox website.
  3. Introduction of exotic competitors and predators (Read more in FROGLOG.)
  4. Pathogens

Amphibians are declining, as are many other groups of life on Earth. This loss of biodiversity should be a cause of concern to all of us. However, there are good reasons for thinking that disappearing amphibians are especially significant.

As a measure of the health of the environment The current global loss of biodiversity is a process generated by the activities of humans. As we modify our environment for our own ends, it is clear that the destruction of the habitats of other species leads directly to their disappearance. However, more recently we have begun to observe, and to speculate about more subtle impacts that human activities may be having, acting at a global level.

We have depleted atmospheric ozone levels; pollutants are accumulating in the natural systems on which we and other organisms depend; we may be altering weather patterns. Such gradual, but fundamental changes are certain to have an effect on the ecosystem. It is possible that amphibians are responding adversely to these changes. They may be showing us how our activities are affecting our shared ecosystem.

Ecologically amphibians are an important part of the ecological balance of many habitats. In the Upper Amazon Basin more than 80 species have been recorded at single sites (more than twice the number found throughout the whole of Europe). In some habitats, particularly in warmer regions, the large biomass of amphibians makes them significant prey items for, and predators of, other species.

The skins of amphibians are yielding drugs useful to medicine. The full potential of such drugs has not begun to be fully appreciated.

Aesthetic Many amphibians are extremely beautiful, and even some of the less beautiful species enjoy considerable public popularity.

Characteristics of amphibians that make them model organisms for biomonitoring

  1. Dual life cycle with quick reproduction.
  2. Porous skin that allows respiration and absorption of environmental factors.
  3. Sensitivity to ultra-violet radiation as a result of their integumentary system.


The Great Lakes Declining Amphibians Working Group is a Regional Working Group of the IUCN/SSC Declining Amphibian Populations Task Force (DAPTF), devoted to investigating the worldwide decline in amphibian populations.
DAPTF publishes the newsletter FROGLOG. Regional working groups promote research and education, and act as information clearing houses.



STUDY METHODS

Study Area Selection And Evaluation

The North American Amphibian Monitoring Project (NAAMP) recommends that a stratified, randomized method be employed to determine sampling locations. It is important to differentiate between a large "area" of similar habitat (e.g., a large bog several hectares in size) and a large area with several discrete but similar habitat types or "basins" (e.g., many farm dugouts - water-filled pits used as watering holes - across a large agricultural landscape) that was to be surveyed. Major waterways of Kansas.

Selection of Habitat should include:

    • A random starting point and direction would be assigned (for practical purposes, these could be randomly selected road intersections)
    • Wetlands along the roadside segment would be identified without prior knowledge of their capacity as amphibian breeding sites.
    • A volunteer or technician would drive or walk the route listening only at the wetlands that were identified in.
    • Wetlands must be a minimum of 0.5 miles apart on both driving and walking surveys. The 0.5 miles distance corresponds to the minimum distance at which an observer is no longer able to hear calling frogs.

An alternative approach might include:

    • A grid would be placed on a map of the area to be surveyed.
    • For each grid wetlands would be identified (see #6 below) without prior knowledge of their capacity as amphibian breeding sites.
    • Wetlands would be randomly selected from the group described and a route would be established among them.
    • Wetlands must be at least 0.5 miles apart

It is best to scout the area during or just prior to the breeding season. The best approach would be to have a separate group establishing the points from those running the surveys.

Changes in Sampling Sites

Wetland breeding sites for amphibians come and go. It is to be expected that some sites will be better over time (for example, beaver activity may form a new pond), and others will disappear (for example, under a new shopping center parking lot). The stops should not be changed to incorporate new sites or eliminate sites that are no longer available. This is important because even if the main wetland is destroyed, other water sources, such as water control pits and drainage ponds, may still provide suitable frog habitat. A review of wetland trends every 5 years should catch any such changes.



Getting To Know a Few Midwestern Amphibians

Click on the scientific name of the amphibian to retrieve pictures, range maps, and calls.

Frogs Toads
Acris crepitans blanchardi
(Blanchards Cricket Frog)
Scaphiopus bombifrons
(Plains Spadefoot Toad)
Pseudacris clarki
(Spotted Chorus Frog)
Bufo americanus
(American Toad)
Pseudacris s. streckeri
(Strecker's Chorus Frog)
Bufo cognatus
(Great Plains Toad)
Pseudacris t. triseriata
(Western Chorus Frog)
Bufo debilis insidior
(Western Green Toad)
Hyla chrysoscelis/versicolor
(Gray Treefrog)
Bufo punctatus
(Red-spotted Toad)
Hyla c. crucifer
(Northern Spring Peeper)
Bufo woodhousei
(Woodhouse's Toad)
Rana areolata circulosa
(Northern Crawfish Frog)
Gastrophryne carolinensis
(Eastern Narrowmouth Toad)
Rana blairi
(Plains Leopard Frog)
Gastrophryne olivacea
(Plains Narrowmouth Toad)
Rana catesbeiana
(Bullfrog)
Rana clamitans melanota
(Green Frog)
Rana palustris
(Pickerel Frog)
Rana u. utricularia
(Southern Leopard Frog)


  1999, KanCRN Collaborative Research Network