Contacts
Elizabeth Slown 505-248-6909, Alisa Shull 512-490-0057, Victoria Fox 505-248-6455
The U.S. Fish and Wildlife Service today designated nine species of invertebrates known only from caves in the northern part of Bexar County, Texas, as endangered under the Endangered Species Act. A species is listed as endangered when at risk of extinction throughout all or a significant portion its range.
"Though not as majestic as the bald eagle or as appealing as the black-footed ferret, these species are unique and fascinating creatures that also serve as good indicators of the overall health of the ecological systems on which humans ultimately depend," said Nancy Kaufman, regional director of the Service’s Southwest Region. "When species like these nine invertebrates begin to disappear from the planet, it is a sign that the natural world around us is under a great deal of stress."
Invertebrates are animals without internal skeletons or backbones such as butterflies, beetles, grasshoppers and spiders. The nine species listed as endangered today include three beetles, five spiders, and one harvestman, a relative of the common household daddy-longlegs. Although small, ranging from less than 2 millimeters to 9 millimeters long, and generally overlooked because they spend their entire lives underground, these invertebrates are biologically and ecologically unique. They resemble creatures out of Tim Burton’s animation, with eyes that are either very small or entirely absent, and bodies that are long and thin, with no coloration (appearing white but actually being transparent).
In 1992, several local groups (Alamo Group of the Sierra Club, Balcones Canyonlands Conservation Coalition, Helotes Creek Association, Texas Cave Management Association, and Texas Speleological Association) petitioned the U.S. Fish and Wildlife Service to add the nine species of karst invertebrates to the List of Threatened and Endangered Wildlife. The nine species are the Helotes mould beetle (Batrisodes venyivi), the Robber Baron Cave harvestman (Texella cokendolpheri), the Robber Baron Cave spider (Cicurina baronia), Madla’s cave spider (Cicurina madla), the vesper cave spider (Cincurina vespera), the Government Canyon cave spider (Neoleptoneta microps), as well as another cave spider (Cicurina venii) and two cave beetles (Rhadine exilis and Rhadine infernalis) that do not have common names.
Three of the species are currently only known from one cave and three others are only known from two to five caves. These species are currently being threatened by the high rates of development around San Antonio and the rest of Bexar County. Development can degrade the cave environment through increased vandalism, contamination from sewer or septic tank leaks, storm water run-off, pesticides or chemical spills. Development can also destroy the cave outright through digging or filling. These species are also threatened by the invasion of non-native fire ants which can prey upon them as well as compete with them for their limited sources of food.
A number of the caves where these species are found are located on the Texas Parks and Wildlife Department’s Government Canyon State Natural Area and the U.S. Army’s Camp Bullis, both of which have expressed an interest in conserving the species on their lands. There are also a number of private landowners who have expressed an interest in conserving the invertebrates on their property. Protection measures for these species will be very similar to those used for a group of cave invertebrates already listed as endangered in nearby Travis and Williamson Counties, Texas, and include such measures as gating cave entrances, protecting the karst area around the cave from contaminant run-off, maintaining a healthy cover of native vegetation on the surface above the cave, and controlling non-native fire ants.
The invertebrates are highly adapted to their underground home, an environment which has a very stable temperature; very high, constant humidity; and little food. The lack of food and stability of their environment leads to an ecosystem with very few species. This makes the cave environment a priceless area for ecological research. Unfortunately, it also means that a sudden change in the environment or loss of a species could quickly wipe-out the entire ecosystem.
Ecologically, cave invertebrates can be described as more similar to large mammals like elephants than to their invertebrate cousins which live on the surface. Like elephants, they have few offspring and live relatively long lives (for invertebrates), a characteristic ecologists call "K-selected." Sadly, this also means that their populations are more sensitive to losing even fairly small numbers of individuals, and that it takes a long time for their population sizes to recover from any catastrophe.
Because plants cannot grow in the blackness of caves, the cave ecosystem is entirely dependent on input from the outside. Food in a cave can come either through animals that cave biologists call "trogloxenes" which roost in the cave but forage for food on the outside, like bats, mice, or cave crickets, or
through organic material like leaves being washed into the cave entrance or filtered in through the ground above the cave. The nine listed invertebrates are probably predaceous and eat the eggs, larvae, or adults of other cave invertebrates.
Cave invertebrates typically also have very low metabolisms, an adaptation to the sparse amounts of food found in their environment. Some biologists have hypothesized that the stereotypical characteristics of cave-dwelling species, such as the lack of pigment (white color) and reduced or absent eyes (blind), have evolved as a measure to conserve energy and channel their limited resources to more useful features like antennae and chemical and touch receptors, which are typically highly developed in cave species. In fact, because they are adapted to an environment with little food, pollution by the addition of large amounts of nutrients to the cave can actually be harmful to the species, because it allows invertebrates that are not cave adapted, such as cockroaches and a variety of flies to survive in the cave and even out-compete the cave species. The healthy cave ecosystem lies in a delicate balance between too little food and too much.
Caves in central Texas form in areas geologists call "karst", areas that lay over limestone rock. Karst terrain typically appears bumpy with knobs and dead-end pits and is sculpted by having the limestone rock dissolved like salt in hot water rather than being eroded by wind or rivers. Karst areas are characterized by sinkholes, "sinking streams" (streams which disappear underground) and springs, as well as by caves.
Caves are the gateways biologists use to study karst because they are large enough for biologists to get into and they have entrances at the surface. Although, these species are known only from caves, they may also use passages that are too small for people or that have no known entrance at the surface. In fact, many biologists more accurately refer to these species as "karst invertebrates. Because of this, areas with sinkholes, other karst features, or limestone rock should be treated with care.
The Service’s decision to list the nine invertebrates is expected to be published in the Federal Register the last week of December. Copies of the final rule are available from the Fish and Wildlife Service Field Office, 10711 Burnet Rd, Suite 200, Austin, Texas 78758 or by calling 512-490-0057.
The U.S. Fish and Wildlife Service is the principal Federal agency responsible for conserving, protecting and enhancing fish, wildlife and plants and their habitats for the continuing benefit of the American people. The Service manages the 93-million-acre National Wildlife Refuge System which encompasses 525 national wildlife refuges, thousands of small wetlands and other special management areas. It also operates 66 national fish hatcheries, 64 fishery resource offices and 78 ecological services field stations. The agency enforces Federal wildlife laws, administers the Endangered Species Act, manages migratory bird populations, restores nationally significant fisheries, conserves and restores wildlife habitat such as wetlands, and helps foreign governments with their conservation efforts. It also oversees the Federal Aid program that distributes hundreds of millions of dollars in excise taxes on fishing and hunting equipment to state fish and wildlife agencies.
Fish and Wildlife Service/Southwest Region
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