Subterranean Fauna
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The
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
of Dinaric Alps. Subterranean fauna refers to Animal, animal species that are adaptation, adapted to live in an underground Natural environment, environment. 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. Both are associated with hypogean habitats – troglofauna is associated with terrestrial subterranean environment (
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 ...
s and underground spaces above the
water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...
), and stygofauna with all kind of subterranean waters (
groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
,
aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...
s,
subterranean river A subterranean river is a river that runs wholly or partly beneath the ground surface – one where the riverbed does not represent the surface of the Earth. It is distinct from an aquifer, which may flow like a river but is contained within a per ...
s, dripping bowls, gours, etc.).


Environment

Subterranean fauna is found worldwide and includes representatives of many animal groups, mostly
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
s and other
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s. However, there is a number of
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s (such as
cavefish Cavefish or cave fish is a generic term for fresh and brackish water fish adapted to life in caves and other underground habitats. Related terms are subterranean fish, troglomorphic fish, troglobitic fish, stygobitic fish, phreatic fish and hypog ...
es and
cave salamander A cave salamander is a type of salamander that primarily or exclusively inhabits caves, a group that includes several species. Some of these animals have developed special, even extreme, adaptations to their subterranean environments. Some speci ...
s), although they are less common. Because of the complexity in exploring underground environments, many subterranean species are yet to be discovered and described. Peculiarities of underground habitat make it an
extreme environment An extreme environment is a habitat that is considered very hard to survive in due to its considerably extreme conditions such as temperature, accessibility to different energy sources or under high pressure. For an area to be considered an extrem ...
and, consequently, underground species are usually less than species living in epigean habitats. The main characteristic of underground environment is the lack of
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
. Climatic values, like
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
and
relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...
, are generally almost stable – temperature corresponds to annual mean temperature in the place where the cavity opens, relative humidity rarely drops below 90%.
Food sources Food is any substance consumed by an organism for Nutrient, nutritional support. Food is usually of plant, animal, or Fungus, fungal origin, and contains essential nutrients, such as carbohydrates, fats, protein (nutrient), proteins, vitamins ...
are limited and localized. The lack of sunlight inhibits photosynthetic processes, so food comes only from epigean environment (through percolating water,
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
, or passive transport by animals). Important food sources in underground habitat are animals being decomposed and bat
guano Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...
, that creates large
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
communities A community is a Level of analysis, social unit (a group of living things) with commonality such as place (geography), place, Norm (social), norms, religion, values, Convention (norm), customs, or Identity (social science), identity. Communiti ...
in such caves.


Ecological classification

Cave dwelling animals show different levels of
adaptation 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 ...
s to underground environment. According to a recent classification, animals living in terrestrial subterranean habitats can be classified into 3 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 A troglobite (or, formally, troglobiont) is an animal species, or population of a species, strictly bound to underground habitats, such as caves. These are separate from species that mainly live in above-ground habitats but are also able to live u ...
): species strongly bound to subterranean habitats; *
troglophile Troglofauna are small cave-dwelling animals that have adapted to their dark surroundings. Troglofauna and stygofauna are the two types of subterranean fauna (based on life-history). Both are associated with subterranean environments – troglofau ...
s: species living both in subterranean and in epigean habitats. Troglophiles are also divided in ''eutroglophiles'' (epigean species able to maintain a permanent subterranean population) and ''subtroglophiles'' (species inclined to perpetually or temporarily inhabit a subterranean habitat, but intimately associated with epigean habitats for some functions); *
trogloxene Trogloxenes or subtroglophiles, also called cave guests, are animal species which periodically live in underground habitats such as caves or at the very entrance, but cannot live exclusively in such habitats."Cave Plants and Animals". 9 December Am ...
s: species only occurring sporadically in a hypogean habitat and unable to establish a subterranean population. Regarding
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 ...
, the corresponding words stygobionts (or stygobites), stygophiles and stygoxenes are used.


Biology

The cave beetle '' Leptodirus_hochenwartii''_(family_ Leptodirus_hochenwartii''_(family_Leiodidae).">Leiodidae.html"_;"title="Leptodirus_hochenwartii''_(family_Leiodidae">Leptodirus_hochenwartii''_(family_Leiodidae). Characteristics_of_underground_environment_caused_cave_dwelling_animals_to_evolve_a_number_of_adaptation_ 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_...
s,_both_
Leptodirus_hochenwartii''_(family_Leiodidae).">Leiodidae.html"_;"title="Leptodirus_hochenwartii''_(family_Leiodidae">Leptodirus_hochenwartii''_(family_Leiodidae). Characteristics_of_underground_environment_caused_cave_dwelling_animals_to_evolve_a_number_of_adaptation_ 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_...
s,_both_Morphology_(biology)">morphological_and_Physiology.html" "title="Morphology_(biology).html" ;"title="Leiodidae)..html" ;"title="Leiodidae.html" ;"title="Leptodirus hochenwartii'' (family Leiodidae">Leptodirus hochenwartii'' (family Leiodidae).">Leiodidae.html" ;"title="Leptodirus hochenwartii'' (family Leiodidae">Leptodirus hochenwartii'' (family Leiodidae). Characteristics of underground environment caused cave dwelling animals to evolve a number of
adaptation 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 ...
s, both Morphology (biology)">morphological and Physiology">physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
. Examples of morphological adaptations include depigmentation (loss of external pigmentation), a reduction of cuticle thickness and the often extreme decrease of eyesight culminating in anophthalmia (complete loss of eyes). Exceptions, however, are harvestmen (Opiliones) in New Zealand caves, which possess large, functional eyes, presumably because these spider-like chelicerates feed on cave-dwelling, light-emitting glowworm larvae ''
Arachnocampa ''Arachnocampa'' is a genus of nine fungus gnat species which have a bioluminescent larval stage, akin to the larval stage of glowworm beetles. The species of ''Arachnocampa'' are endemic to Australia and New Zealand, dwelling in caves and gr ...
'' which they detect visually. Other adaptations include the development and elongation of antennal and locomotory appendages, in order to better move around and respond to environmental stimuli. These structures are well endowed with
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...
,
tactile Tactile may refer to: * Tactile, related to the sense of touch * Haptics (disambiguation) * Tactile (device), a text-to-braille translation device See also * Tangibility, in law * Somatosensory system, where sensations are processed * CD96 CD ...
and humidity
receptors Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a n ...
(such as Hamann's organ in the cave
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 ...
''Leptodirus'' ''hochenwartii''). Physiological adaptations include slow
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 ...
and reduced
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
consumption, due to limited food supply and low energy efficiency. This is likely to be realized through reducing movements, erasing aggressive interactions, improving feeding capability and food usage efficiency, and through
ectotherm An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life a ...
y. As a consequence, cave dwelling animals can resist without eating for long time, live more than comparable epigean species,
reproduce Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual org ...
late in their lifespan, and produce fewer and bigger
egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s.


Evolution and ecology

Subterranean fauna have evolved in isolation.
Stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostrati ...
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, subterranean fauna habitat and food availability can be very disjunct and precludes the great range of observed diversity across landscapes.


Threats to subterranean fauna

Floodwaters can be detrimental to subterranean species, by dramatically changing the availability of habitat, food and connectivity to other habitats and oxygen. Many subterranean fauna are likely to be sensitive to changes in their environment and floods, which can accompany a drop in temperature, may adversely affect some animals. Humans also pose a threat to troglofauna. Mismanagement of contaminants (e.g. pesticides and sewage) may poison subterranean fauna communities and removal of habitat (e.g. rising/lowering of the watertable or various forms of mining) can also be a major threat.


See also

*
Cave conservation Cave conservation is the protection and restoration of caves to prevent or minimise the effects of human activities. Some caves have delicate features that can be disturbed by changes in light levels, humidity, temperature or air flow. Caves that ...
*
List of troglobites A troglobite (or, formally, troglobiont) is an animal species, or population of a species, strictly bound to underground habitats, such as caves. These are separate from species that mainly live in above-ground habitats but are also able to live u ...
*
Speleology Speleology is the scientific study of caves and other karst features, as well as their make-up, structure, physical properties, history, life forms, and the processes by which they form (speleogenesis) and change over time (speleomorphology). ...
*
Subterranean river A subterranean river is a river that runs wholly or partly beneath the ground surface – one where the riverbed does not represent the surface of the Earth. It is distinct from an aquifer, which may flow like a river but is contained within a per ...
*
Trogloxene Trogloxenes or subtroglophiles, also called cave guests, are animal species which periodically live in underground habitats such as caves or at the very entrance, but cannot live exclusively in such habitats."Cave Plants and Animals". 9 December Am ...


References

{{reflist, 24em Cave animals Subterranea (geography) Animals by adaptation Animals by location Ecology