Biospeleology of the Piemonte
(North-western Italy)

Systematic Photographic
Atlas

   
Web page created and updated by Enrico LANA
   
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An outline of Biospeleology

History

Ecology and environmental factors

Trophic and biospeleological categories

Hypogean evolution

Biogeography


Ecology and environmental factors


Elements of Ecology

The whole of geographic areas adapted to the life of the organisms is called biosphere; it is constituted from the atmosphere, the waters and the ground.

The living beings are influenced from many environmental factors and the physical characteristics of a certain ambient situated in one geographic zone are determining and constitute by precise limits for the life.

One geographic belt characterized by a predominant vegetation that influences also the animal life is called biome and every biome has, consequently, its characteristic species.

In every biome it's possible to identify different ecosystems, that are the bio-environmental units constituted by living beings that interact among themselves and with the physical environment.

The ecosystem constitutes the integration of a collectivity of several species (animals and vegetables), called biocenosis, with the environmental space in which they live (biotop). The biotop is therefore the territory in which the biocenosis lives and, whereas, the biocenosis is the whole of organisms that live in the biotop. The biotop it therefore the fundamental environmental unit and it is topographically possible to delimit it and it is characterized by the biocenosis that live in it.

The environment is the totality of the external abiotic factors that form the space in which the organisms move and live. The environment, in fact, cannot be conceived without the living beings that populate it and that, in greater or smaller measure, modify it: close relations and strong influences exist between abiotic environmental factors and biotic factors.

The biotic factors, relative to the biosphere, derive from the qualitative and quantitative presence of plants and animals; are biotic factors the single individual, its population, the whole of various populations and the relationships among them (competition, predation, etc.).

The abiotici factors, are instead relative to the litosphere, to the atmosphere and the hydrosphere, they are inorganic components whose influence can be highlighted through the action of simpler components:

- the air, its chemical composition, the pressure, the temperature and the humidity;

- the rock, its morphology, the chemical and mineralogical composition, the structure, and sometimes also its spatial conformation;

- the water in its physical states and in the phases of its cycle, that is evaporation, condensation, precipitations and outflows over and under the land surface.

An other fundamental abiotic factor, by extraterrestrial origin, is the solar radiation, that acts directly and indirectly on all the biotic and abiotic components of a system. In a speech of biospeleological subject in which the direct influence of the sun would seem minimal, we must consider that in the first place the water that has dug the caves, has been put in motion from the solar heat with the thaw of the snows from which comes and that in a generalized manner, except certain bacteria, the organisms that live in the caves consume the rests of other organisms that have stored in the outside environment the solar energy in their bodies.

Usually an ecosystem has one natural border: ecosystems are, for example, a particular meadow in a grassland, a water pool in a beach subject to the tide, a decaying trunk in a forest or, in the hypogean environment, an active gallery in which flows the underground river. An ecosystem can exist for a certain period of time, only if a delicate equilibrium is established between abiotic and biotic factors.

The underground ecosystem, is delineated by precise features:

- the total absence or reduction of some factors (like light, for example);

- the steadiness in the time of other factors (i.e. temperature, humidity);

- the simplicity in the composition of an animal population;

- the consequent simplification of the synecological relationships (i.e. between the levels of one alimentary pyramid);

- the greater degree of isolation in respect to the contiguous ecosystems.


Hypothetical example of alimentary chain in one cave
without contributions from the external world.


Hypogean habitats

In an ecosystem there are various spaces in which an organism can live (i.e. the water of a pool, the mud of the ground, the cavern's walls, etc.). Every organism live therefore in a particular portion of the ecosystem, it says that it has its habitat , that is the physical place in which the biotic and abiotic environmental factors are congenial to the survival of the species which it belongs. Moreover every organism, in its environment, supplies to the own necessities in various ways (so we have organisms producers, decompositors, predators, detritivore, etc). The whole of the relations between organism and atmosphere constitutes its ecological niche . Obviously, two species cannot occupy the same niche.

We must not confuse habitat with biotop: while the habitat is the ideal place of life of an individual or a species, the biotop is is the real place of life of a community of individuals or more species, that is of a biocenosis.

With the adjective "hypogean" we define the underground environment, the habitat of the organisms living under the surface of the ground, while the "epigean" environment is the habitat of the organisms living over the surface of the ground. Sometimes the separation between the two environments isn't evident, not as well as from a morphologic point of view, but rather from the ecological one. For example we can think to the bottom of a canyon, the bottom of one little valley very deep or to the bottom of one deep doline: there is little light, stabler temperature that in the outside and probably a lot of humidity.

These environment are very similar to the liminar zones of the caves (in proximity of the entrance), zones that, in the attempt to make a subdivision of the hypogean environment, can be defined "of transition".





In the figure above the progressive letters A-B-C1-C2 indicate the layers according to the pedological classification; the term "suolo" (ground) is synonymous of rizosphere.

First of all we distinguish the endogean environment . It represents the portion of ground comprised between the inferior limit of a detritus vegetable and the inferior limit of the roots of the arboreal plants and for this is also called rizosphere; it is the more superficial part of the ground in contact with the epigean environment. Its aspect can be full of rocks, friable, gravelly, argillaceous, often mixed, it depends of the geologic nature of the ground, the morphology, the altitude, the vegetation and other factors; it can have thickness of little decimeters, like in the alpine pastures, or of some meters, like in the boschive valleys. Almost always this environment recalls the characteristics of the hypogean environment, like the temperature, the humidity, the absence of light and it represents for the fauna an ideal habitat being rich of humus and of varied organic substances. Here lives the greater number of interesting species from the biospeleological point of view.

Biologically, in base to the physiology and to the morphology, we distinguish the subterraneaa fauna in two categories: endogean and cavernicole or hypogean. In fact the endogean arthropods have a degree of specialization smaller than the true troglobites and their stage less evolved represents one transition from the epigean life to the hypogean. The endogean environment isn't clearly distinguished respect to the contiguous sectors of the ground, and the endogean fauna is not easily distinguished from the cavernicole one: we can see several stages of evolution, and also species not clearly traceable to one or the other type of fauna.

The environment of cave or hypogean indicates instead the cavities accessible to the man. A satisfactory division of the hypogean environment could be gained from the confluence of elements depending to the environment, but important from the ecological point of view like the trofical situation, the hypogean meteorology, the stratigraphy, etc, without to omit the morphology of the environment, but we must remember that for an arthropod a cavity of 5 or 50 cm is not much different, while for one speleologist the issue of the dimensions is essential.

According to the opinion of many authors (es. Racovitza), we find, besides the endogean and hypogean, also the land interstitial environment, very interesting, especially that labirinthic part of microfissures that operates from natural filter of the exogenous contribution; it operate as a shelter for the more delicate living forms, and it prevents to violent air exchanges between outside and inside. A lot of persons think that the organisms founded in cave live only in cave, but many species live in truth in the neighbouring interstitial environment, from which irregularly they reach in cave. For this reason many arthropods of the hypogean fauna are thought rare. The speleologist enters very rarely in cave like the bugs, and that remarkably lowers the possibility of a contact. However there is a particular fauna that needs the cavernicole environment, because its way of life demands a larger space: as an example the spiders for to weave their cobwebs, the troglophile grasshoppers for their particular walking, some species winged of dipters and trichopters, the bats.

The phreatic environment is the zone interested instead from the groundwater stratum; it is often subject to seasonal variations of level as a result of meteorological contributions and it interests the fauna mainly aquatic. The rains in particular exercise a remarkable action of water connection between several epigean and hypogean systems and determine one greater hygrometric uniformity favoring these contacts.



Hypogean environmental factors

We pass to examine more in detail the environmental factors that influence the life in the underground environment.

The abiotic factors are the physical and ecological characteristics of an environment and they born, vary and decay in harmony with the mutation of the same environment. We think as an example to an ideal cave that with passing of the millenia arrives to the total collapse of the vault: geologically it is transformed in valley, the dark disappears, the humidity diminishes, the temperature loses its steadiness.

In the hypogean environment there are factors of primary importance, that remarkably influence the ecology of the system; the biocenosis is closely linked to the becoming of the same factors, for the restrictive effecst and for the indirect action of evolution.

Therefore the fauna of a cave is not accidental, but it represents instead the result of a series of natural phenomena, of the physical and chemical laws and still more of geologic events. Only the knowledge of all this entirety can give answer to the multiple questions on the composition of one certain biocenosis.

Darkness, temperature, humidity are the abiotic factors more important. These factors, being often constant for a sufficient period of time (of the order of the millenia) are determining for the hypogean biological evolution.


Darkness : only few caves with a certain morphology are partially illuminated, in all the others caves, and mainly in the land interstitial environment, the absolute dark reign. An immediate consequence is the gradual reduction of the vegetation in the liminar zone of the cave with total disappearence of the green plant where the light is too faint for the chlorophyllian photosynthesis.

Without vegetation it lacks the primary production insured outside by the green plants, and also all the phytophage organisms with its parasites and predators. Exceptionally the production of organic substance is present thanks to one meagre bacterial action. Sometimes we can found, also in depth, sporadic fungi, which aren't plants, and don't produce from himself the vital bases, but are saprophyte and they absorb organic substance from dead organisms or in decomposition or also from alive organisms (parasite fungi). The cavernicole fauna is therefore forced to found elsewhere the energetic resources and shows adaptive modifications of the metabolism. Many experiments are made in order to assess the effects that the light causes on these organisms: for some of them it has a lethal effect.

The anophthalmy (the loss of the eyes and the luminous receivers) is one of most important evolutionary consequences of the light absence.

The mole, insectivore, hunting in the endogean environment and sometimes in surface too, but only at night: the visual apparatus is reduced, but the sense of smell is very developed. Contrary in the Tarsius (primate that lives in the Indo-china) the visual organ is very developed, since it is insectivore and hunting bugs in thick and shady forests with insufficient lighting while its sense of smell is limited.

Moreover, the greater part of the true troglobites shows a lengthened habitus, with slim body and long legs and antennas, covered of long sensory bristles for to compensate with an increase of the tactile and olfactory senses the lack of the eyes that are useless in the obscurity. The difference is obvious if we confront trogloxene epigean insects with the correspondents troglobites that, even so they belong to the same family, they have evolved for million of years in the hypogean environment.

 

 

The depigmentation is another consequence of the light absence and many specialized insects have a clear brown color opposed to the dark liveries of the epigean species. Another consequence is the gradual and sometimes very conspicuous reduction of the chitin, an ammino-polisaccaridic substance that make leathery the exoskeleton, since the solar light contribute to its formation.

Other effects are recorded also in the metabolism: it disappears the alternation of the day and the night, with modification therefore of the nictemeral rhythms .


Temperature : in the hypogean environment the temperature is very stable; in the interstiziale environment, that is lacking in airflows, it is stabler than in the caves.

Normally the temperature of a cavity basement corresponds to the average annual of the external temperature of the locality in which the cave is situated and it depends therefore on the latitude and the altitude. It depends also on the conformation and the depth of the cave: the ascending caves are warmer than those descendants.

In the deep caves very rarely we can observe an increase of the geothermal degree with the depth: probably it is correlating with an intense fissuration of the limestone rock that allows the infiltration of external air and water.

In the caves with more openings the seasonal thermal variations influence the inner atmosphere considerably.

The experiments have demonstrated that the cavernicole arthropods are not strictly stenothermic (that is influenced by little variations of temperature): some of them normally live to limit temperatures , therefore they can survive within enough wide limits of temperature; some arthropods are able to bear changes of 10░C for periods of more days, but this is possible only if the other factors, like obscurity and humidity, are constant.

The temperature has an important role in the metabolism of some species: as an example in the bats when they go into hibernation.

Humidity: it is a very important factor without doubt; in most of the dry caves, as an example in those fossils, the environment is azoic.

Normally the cave's atmosphere shows values around 95% of relative humidity. There is a typical seasonal course in the endogean environment, this is due to the fact that it is in contact with the epigean environment and therefore to the external meteorological situation; various species of arthropods is forced to migrations towards the interstitial for having a favorable humidity; such species very rarely are found in the cavernicole environment and a searcher that want to capture them must to dig to the outside in May and June during the period of rains.

The dry caves are generally azoic: the troglobites live usually in conditions of humidity saturation and are therefore stenohygre; they can die for small variations of the humidity degree; this is due to the dehydration. Every organism needs a certain degree of humidity and pressure that not always coincide to the environmental one.

Those insects that in the summery period lives under the cooking sun, without an appropriated exoskeleton, would die dehydrated in little time. Some species (crustaceans) are so adapted or preadapted to the strong humidity that can lead amphibious life, but this advantage obligates them to a constantly humid environment.

These three main factors (darkness, temperature, humidity) are locally influenced by other geographic and geologic factors which:

- latitude (on which rainfall and temperature depend);

- altitude (on which temperature, vegetation and exogenous contribution depend);

- geologic nature of the ground (substratum, potential, stratigraphy, acidity);

- morphology of the cave (vertical, with wide doline opening or horizontal with small entrance).

Other abiotic factors can be: the chemical composition of the air and its state of agitation; the water, present as running water, firm water or dripping from the roof of the caves; the salinity and the pH of the water ; the lithological factors and the physical nature of the ground (granulometry, porosity, power of imbibition).




An outline of Biospeleology

History

Ecology and environmental factors

Trophic and biospeleological categories

Hypogean evolution

Biogeography


    Glossary
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SPECIFIC
BIBLIOGRAPHY
      
BIOSPELEOLOGICAL
BIBLIOGRAPHY
      
GENERAL
BIBLIOGRAPHY


Biospeleo SUMMARY

Systematic Index

 

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