Troglofauna are small

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

-dwelling

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s that have

adapted In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...

to their dark surroundings. Troglofauna and

stygofauna Stygofauna are any fauna that live in groundwater systems or aquifers, such as caves, fissures and vugs. Stygofauna and troglofauna are the two types of subterranean fauna (based on life-history). Both are associated with subterranean environments ...

are the two types of subterranean fauna (based on life-history). Both are associated with subterranean environments – troglofauna are associated with caves and spaces above the water table and stygofauna with water. Troglofaunal species include

spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

s, myriapods and others. Some troglofauna live permanently underground and cannot survive outside the cave environment. Troglofauna adaptations and characteristics include a heightened sense of hearing, touch and smell. Loss of under-used senses is apparent in the lack of pigmentation as well as eyesight in most troglofauna. Troglofauna insects may exhibit a lack of wings and longer

appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

Ecological categories

Troglofauna are divided into three main categories based on their

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...

: * Troglobionts (or troglobites): species, or populations of species, strictly bound to subterranean habitats. * Troglophiles: species living mainly aboveground but also in subterranean habitats. These are further divided into eutroglophiles (aboveground species also able to maintain a permanent subterranean population) and subtroglophiles (species inclined to perpetually or temporarily inhabit a subterranean habitat, but strongly associated with aboveground habitats for some functions). * Trogloxenes: species only occurring sporadically in an underground habitat and unable to establish a subterranean population.

Environment

Troglofauna usually live in moderate cave regions. The overall climates of these caves do not significantly change throughout the year. Humidity in such caves is generally high ranging from 95 to 100 percent; evaporation rates are low. The cave ecosystem in which troglofauna reside can be divided into four zones: entrance, twilight, transition and deep cave. The entrance zone is where the surface and underground environments meet. Light becomes scarcer in the twilight zone. The transition zone is almost completely dark; however some outside environmental effects can still be felt. Finally, the deep cave zone is completely dark, relatively stable, and exhibits no evaporation. Troglobites are usually found in the deep cave zone.

Diet and lifecycle

Troglofauna have adapted to the limited food supply and are extremely energy efficient. Food is found from "twigs, leaves, bacteria and

epigean Epigeal, epigean, epigeic and epigeous are biological terms describing an organism's activity above the soil surface. In botany, a seed is described as showing epigeal germination when the cotyledons of the germinating seed expand, throw off the ...

animals (including

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

)." Food is also found from trogloxene carcasses, egg deposits, and faeces such as bat guano. Troglofaunal beetles are predators and may feed on other troglofaunal animals rather than bacteria, twigs and guano. Francis G. Howarth hypothesized on adaptations troglofauna have made to exist in the cave environment, postulating that troglofauna "have lost many of the water conservation mechanisms of surface relatives, and more nearly resemble permanently aquatic arthropods in water balance mechanisms, including cuticular permeability." Troglofauna thrive in a humid environment and when a "chamber is too dry ... animals display either agitated or comatose behavior", indicating they are highly susceptible to changes in temperature and humidity. To survive in an environment where food is scarce and oxygen levels are low, troglofauna often have very low

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

. As a result, troglofauna may live longer than other terrestrial species.

Reproduction

Reproduction varies by species and may be infrequent, but very little is known.

Evolution and dispersal

Troglofauna have evolved in isolation. Stratigraphic barriers, such as rock walls and layers, and

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

barriers, such as rivers and streams, prevent or hinder the dispersal of these animals. Consequently, troglofauna habitat and food availability can be very disjunct and precluding a great range in diversity across the landscape.

Species

Troglofaunal species include representatives of many animal groups, including

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s, millipedes,

pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. Pseudoscorpions are generally beneficial to humans sin ...

s, harvestmen, isopods,

collembola Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ento ...

ns, diplurans,

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

s and

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...

s. Troglofaunal gastropods are endemic to the U.S. and in Europe; they are mostly concentrated in the northeastern Mediterranean regions. Troglofaunal scorpions are mostly found in Mexican caves. Troglobitic spiders are found more widespread in the U.S., Europe, and Japan. However, they are also found in Mexico, Congo, Cuba, Australia, and the Philippines. Troglofauna are found worldwide. Troglofaunal salamanders are found in Europe and the U.S. Approximately 90% of caves worldwide remain undiscovered due to lack of visible entrances and more habitat exists in fissures, vugs and other spaces above the watertable. Consequently, many species of troglofauna may not have been discovered.

Discovery

In more recent times, more troglofaunal species are being identified. In Sequoia and

Kings Canyon National Park Kings Canyon National Park is an American national park in the southern Sierra Nevada, in Fresno and Tulare Counties, California. Originally established in 1890 as General Grant National Park, the park was greatly expanded and renamed to Kings ...

s of

Sierra Nevada mountains The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley (California), Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Cars ...

, California, scientists recently discovered 255 new caves, and 30 undescribed invertebrate species – "an extraordinary number for such a small area".

Threats to troglofauna

Floodwaters can be detrimental to troglofaunal species, by dramatically changing the availability of habitat, food and connectivity to other habitats and oxygen. Many troglofaunal species are likely to be sensitive to changes in their environment and floods, which can accompany a drop in temperature that may adversely affect some animals. Extreme winter temperatures may affect troglofaunal species near the surface. Birds and bats in caves prey on troglofauna. Troglofauna are likely to compete with each other for survival. Humans also pose a threat to troglofauna. Mismanagement of contaminants (e.g. pesticides and sewage) may poison troglofaunal communities, whilst removal of habitat, either directly or indirectly (e.g. rising watertable) is also a major threat.

References

External links

"Flora and Fauna of Caves: Troglobites" at Showcaves.com

* {{Cite Americana, wstitle=Cave Animals, author=Ernest Ingersoll, author-link=Ernest Ingersoll, short=x Cave animals Subterranea (geography)