Biospeleology
Biospeleology is the study of organisms living in caves (Duckeck, 2004). There are four types of organisms that may be found in caves. Animals that permanently live in caves are confined to caves and are unable to live outside of the environment are called troglobites (Duckeck, 2004). Trogloxene animals enter caves causally to escape predators or the warm sun in the summer (Lana, 2004). An animal that uses a cave for a part of its life cycle is called a troglophile (Duckeck, 2004).
Caves have stable environments. Characteristics ranging from temperature with about a 3 ˚C range of temperatures from about 7 ˚C -10 ˚C. The elimination of photosynthetic activity, high relative humidity and low rates of evaporation all create a cave’s stable environment (Holsinger, 1998). For some species a stable environment such as a cave is prime.
Cave Inhabitants
Trogloxene
Bats are Trogloxenes and spend the winter in caves to hibernate. Three types of bats, Eastern Pipistrelle, Little Brown and Northern Myotis, inhabit Crystal Cave between September and April for hibernation. Bats mate in the fall and then go into hibernation. While in hibernation, they will wake up about every twenty-five to thirty days. While in hibernation the bats live off their body fat. They can eat about three thousand bugs a night when feeding. If the bats are disturbed in the caves, they will lose body fat and leave early, often to their death. In the spring the eggs will be fertilized and the young will be born from late May to June.
Eastern Pipistrelles are the first to enter hibernation each fall and the last to leave the caves in the spring (Figure 1). During hibernation they live off body fat. Eastern Pipistrelles prefer to hibernate alone in caves. They also may choose the exact same spot in a cave year after year (BCI, 2002). There are approximately sixty to eighty Eastern Pipistrelles hibernating in Crystal Cave each winter (Figure 1). The Northern Myotis is also a solitary bat in caves or is found in small groups (Figure 2). The Little Brown often forms colonies with hundreds of bats (BCI, 2002) (Figure 3).
Troglobites
These are species that have been confined to cave life and form adaptations in order to survive life only in caves. The adaptations are ones that will allow great struggle for species to live outside of the cave. Fish, salamanders, insects, spiders will have reduced eyes and in most cases no eye sight (Figure 4). In dark caves eye sight is not needed. Troglobites have great senses of smell and touch allowing a more efficient life for cave dwelling animals. Characteristics such as elongation of antennae and bristle covered legs give the species abilities unlike those of species similar to them above the surface (Hurd, 2001).
An interesting aspect of Troglobite’s lives are the possibility that species of such could have survived in the caves as other species above ground became extinct. Changing conditions on the earth largely effects the surface environments, whereas protection of species living below the surface in cave environments will most likely remain relatively stable over long periods of time (Holsinger, 1998). These species may have occurred protected against many perturbations that effect surface environments. Evidence of Troglobite species that once lived in the cave and had been well preserved in the stable cave environment (Figure 5).
Troglophile
Troglophile’s are animals that like to live in caves but are also widely seen above ground. They are attracted to the caves because of the moist and dark environment. These species are then commonly seen above ground in dark damp areas, such as under logs, rocks (Kramer, 1995). Differences between Troglophiles and Troglobites are the pigmentation and eye sight (Figure 4).
Food For Cave Dwellers
Unlike the bats that live in the caves during the winter months which are using the cave as a hibernation location and have stored food, other cave dwellers need nutrients to survive. There are two main ways basic food resources become available in most ecosystems (Holsinger, 1988):
Stream Flow. Nutrients may be transported by streams that enter caves through sinkholes and other openings in the cave formation. Openings can be intense factor when flooding occurs and strengthens the velocity of the waterways.
Percolation. Percolating groundwater enters the caves. Water passes through crevices and fissures holding nutrients in its liquid through the material above the cave.
Decompositional material. Species in the cave will feed off of bat guano and dead species in the cave.
Figure 1. (Left) Distribution Range of Eastern Pipistrelle Bats in North America. (Right) A picture of an Eastern Pipestrelle . * Isolated or questionable record of bat inhabitants (BCI, 2002).
Figure 2. (Left) The distribution of Northern Myotis around North America. (Right) A picture of a Northern Myotis. * Isolated or questionable record of bat inhabitants (BCI, 2002).
Figure 3. (Left) The distribution of the Little Brown around North America. (Right) A picture of a Little
Brown. * Isolated or questionable record of bat inhabitants (BCI, 2002).
Figure 4. Notice the coloration of the pictures in the left column compared to those in the right column. The pigmentation of the troglobites to the left is very dull. The coloration is an adaptation to cave life. Troglophiles (right) on the other hand are colorful and resemble species above surface. They are able to adjust from habitat to habitat (USGS, 2002).
Figure 5. Well preserved fossils of species that survived many
years after surface species died off.
Cave Flora
Characteristics of caves do not make life possible for trees, grass, or ferns. Photosynthesis is not a process that occurs in dark, damp places (Kramer, 1995). Although there is no sign of photosynthetic plants in the deep cave itself, flora largely exists in the entrance of the caves. Near the entrance of the cave there is a gradual decrease of light intensity with increased distance from the opening. As you move farther into the cave you find less and less flora (Figure 6). The lack of photosynthesis creates a lack of chlorophyll. The absence of chlorophyll may cause species to lose their pigmentation and have a whitish or pale yellow color (Ford, 1976).
The flora found deep in caves is generally flora inhabited in other environments above the surface with low amounts of light. These species have adapted to a cave environment to allow inhabitance in caves. Most of these species are varieties of fungi and bacteria that have adapted to life in a cave (Figure 7).
Fungi and bacteria receive the energy needed through animal droppings, dead animals, leaves, stems, and twigs carried through by stream water (Kramer, 1995). In cave inhabitants where humans venture through there are higher rates of exotic fungi that is accumulating (Ford, 1976). At Crystal Cave where we went on a field study there was few evidence of human induced life (figure 8). Fungi is critical in providing food sources to other species in the cave (Ford, 1976).
Figure 6. As the light intensity decreases moving away from the mouth of the cave, less evolved flora is found. Once you get to the point where is an absence of light penetrating into the cave you only find fungi and bacteria (Ford, 76).
Figure 7. Evidence at Crystal Cave of human induced
flora growth.
Figure 8. Picture of fungi using bat guano as a source
of energy to survive in a cave (Kramer, 1995).