Texella reddelli
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| Bee Creek Cave Harvestman Fossil range: Late Pleistocene - Recent |
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The Bee Creek Cave Harvestman or Texella reddelli was added to the endangered species list on September 16, 1988. They were added at the same time as 6 other species native to the Karst Ecosystem in Travis County and Williamson County, Texas. They are classified as Troglobites, meaning they spend their entire lifespan underground. They inhabit areas near 100% humidity with constant temperatures. Since they prefer the darkest parts of the caves, they prey on Collembelums, which are small arthropods. Since they can only be found underground, research on these creatures is difficult. Their distribution is very limited and unknown reproductive rates make them very susceptible to habitat destruction and other threats. The number of individuals unknown but they only exist in about 7 caves. Texella reddelli are found on both the North and the South of the Colorado river which would be a major obstacle for Troglobites. This is the only specie that is known to exist on both sides of the river. Texella reyesi used to be considered T. reddelli because of there similarities when it was originally placed on the list, but since has been identified as different and now is also on the endangered species list. The Texella reddelli occurs in only three caves in the Jollyville plateau and four caves in the Rollingwood region. Those that were originally thought to be T. reddelli, but now are renamed Texella reyesi occur in Tooth, McDonald, Weldon, and Root caves.
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[edit] Description
They are about 1/8 of an inch with a yellow-brown in color and long legs. The young ones have an yellowish-white body. There are six other invertebrates that are similar and they are known as troglobites, which means that they spend the entire lives underground, have small eyes, and elongated appendages. All seven of the species live in the Karst ecosystem in Travis and Williamson Counties.
[edit] Habitat
Their habitat is limestone caves. They are only able to survive in caves that maintain a stable temperature and humidity (close to 100%) . They have been known to exist in caves both to the north and south side of the Colorado river. The river would be a major obstacle for such a small invertebrate to cross. They live in 'karst' type of terrain in Travis County, which is formed by "dissolution of calcium carbonate from limestone bedrock by mildly acidic groundwater." This process creates the caves that are needed to support this species. They receive there their nutrients through groundwater infiltration.
[edit] Threats
The main threats to this small invertebrate is habitat loss due to urban development. Pollution also threatens the caves that they live in. Pollution and vandalism also threatens the caves that they live in. The introduction of fire ants has been devastating on small invertebrates such as the Bee Creek Cave Harvestman. The fire ants are aggressive predators and the the habitats in which the Harvestman live, small caves near the surface, make them easy targets.
[edit] Recovery
To focus on the future of these several species, we need to protect the key areas of the Karst ecosystem that they live in. We need to be able to target areas the that have a high amount of species diversity. Areas that are chosen should not be close together in case of disaster and to protect genetic diversity. We need to protect them from contaminated ground water and other non-native predators such as the Fire Ants. Fire ant activity has increased since these were placed on the endangered species list. The Fire ant is an aggressive predator and it has devastating and long lasting impacts on native ant and arthropod communities. The shallow caves makes them vulnerable to invasion by fire ants and other exotic species. Fire ants have been found in over 50% of the caves that are known to contain endangered species in this ecosystem. Even if the Fire ants do not always directly prey upon the the Texella reddelli, their presence can have a negative effect on the ecosystem and species that are critical in the food chain
[edit] Location
Since 1988 when these species were listed as endangered, studies have resulted in the finding of more areas with these species along with new endemic species. Due to the intensive requirements to find caves, much of the Karst area has not been searched. To date over 700 Karst features have been located in 2 counties in Texas, while only 100 of these are believed to contain endangered species. While we may increase the number of locations in which these endangered species are found. The range of each species is not expected to increase.
[edit] Troglobites
Troglobites are thought to have evolved over the last 10,000 to 2,000,000 years, when invertebrates moved into the more stable cave environments. These species survived in the cave environment and adapted to it. The Karst terrain created caves that were not always connected with each other. This brought about "islands" of individual populations that were not connected. Over time the separate groups became different species because of the isolation. The rate are which speciate was different. The species that are more mobile have larger ranges and are less isolated. Since they are all still relatively close together, disturbances can make them highly susceptible to extinction. They require stable temperatures and often stay in remote corners or the ceiling of the cave that are the warmest.
[edit] Karst
The Karst ecosystem is provided water by surface drainage and groundwater. The water travels rapidly through cave openings and fractures. This provides very little or no purification which can leave the cave susceptible to pollution from contaminated water. This is a problem in certain areas where runoff can be a problem or in agricultural areas where herbicides and pesticides are used. Contaminants are one or the main threats along with urban development.
In the Karst ecosystem the surface communities are very important for photosynthesis. These plant and animal communities are essential for nutrients and energy, Nutrients travel from the surface in the form of organic debris. the surface plant communities around this ecosystem can range from pasture land the woodlands. Exotic plants and animals are detrimental to native species because they compete for food and decrease overall species diversity. The surface community also serves as a buffer against temperature and moisture change and can filter out some pollutants.
[edit] Threats
By protecting native vegetation we may also help control non-native species, that could compete or prey upon endangered species. Fire ants are especially detrimental to the Karst ecosystem. The main threat to the species is loss of habitat to urban development. The area in which the species occur is going through urban expansion at a rapid rate. Very few of the caves are capable of handling a change and many of the caves already occur close to developed areas, such as roads, schools, houses, golf courses, and commercial centers. Changes in drainage patterns along with increases in pollution could cause a collapse of caves. Although some caves have already been filled or collapsed, it is hard to estimate how many have already been lost. Elliott and Reddell (1989) estimate that 10% of caves in Travis County are destroyed every 10 years. Development activities that result in the alteration of natural drainage patterns can negatively effect these species. This can include altering the Topography, increasing or decreasing cover, irrigation systems, and other activities.
