The Demise of Colorado's Fragil Ancylid
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Nongame biologists are worried about the fragil ancylid, a mollusk species that once lived in Colorado, but can't be found today. They're concerned that Colorado may be losing a native resident before we learn to appreciate its importance to the ecosystem. In fact, some biologists believe that Colorado's fragil ancylid represents the situation facing many mollusks and amphibians worldwide.
Shi-Kuei Wu, invertebrate zoologist with University of Colorado and noted authority on mollusks, recently completed an inventory of Colorado mollusks for the Division of Wildlife. He found 41 different species, two of which are in serious trouble. The fragil ancylid was last collected by G.W. Bryce, Jr., in 1965 in Yuma County's Stalker Lake, its only known Colorado habitat. Just 4 mm long, its shell provided only partial protection from predators and the surrounding environment. In 1989, Wu could not find any fragil ancylids in Stalker Lake.
The rare Rocky Mountain capshell is the only North American species in its family (Acroloxidae). First found in Colorado in 1920, the capshell was not seen again in Colorado for 50 years, when Bryce discovered 72 individuals per square meter in Peterson Lake. Today Peterson Lake, located at the base of Eldora Ski Area, is highly eutrophic (rich in dissolved nutrients and deficient in oxygen); Wu could locate only one capshell after 90 minutes of intensive search on the least affected shore. He reported, "Because of increasing commercial development in the vicinity of Peterson Lake, and concurrent rapid decrease in its population density, this relict species is greatly endangered."
A Biological Early Warning System
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Biologists—those people who study living animals in the hinterlands and keep accurate records by constantly jotting in pocket-sized, spiral notebooks—are finding that the populations and distribution of many animals they study are declining in Colorado and all over the world.
For example: Boreal toads used to be so abundant in the Rocky Mountains of Colorado and Wyoming that you couldn't walk down the trail without seeing them. Now they are difficult to find. Populations of tiger salamanders seem to be declining in high Colorado lakes. Frogs at a field research station in Brazil were once abundant and diverse. In 1982, a returning biologist found that of the 30 common frog species, 6 had disappeared completely and 7 had dramatically reduced populations. Similar trends are evident in frog populations in Colorado's high country.
What really worries biologists is that significant numbers of animal populations are declining even in pristine, protected areas. The fact that mollusks and amphibians—animals that have survived on Earth since the time of the dinosaurs—are now dying out, is of primary concern to biologists. These species may be serving as an early warning system regarding what our polluted environment is doing to every animal on Earth, including the human animal.
In order to understand what the fragil ancylid and the Rocky Mountain capshell are telling us about Colorado, we need to know more about their populations and life requirements. However, limited resources put DOW priorities elsewhere. DOW Nongame Biologist Jim Bennett sums up the problem this way: "We need to know the status and biology of these animals before decisions are made about management priorities. Such decisions should be conscious and knowledgeable, not based on tradition or assumption.
Next: Keep Your Eyes Peeled
(The information contained in these issues of Colorado's Wildlife Company was accurate at the time of original publication. Situations and circumstances described, staff positions, contact information, and dates of some events may have changed in the interim. Present knowledge and understanding of biological and behavioral facts and information may also be different, now, than presented here.)