Tom Garcia
Ecological Priciples Professor William J Cromartie
Cave Ecosystems of the World
Cave ecosystems are among the most diverse ecosystems I have studied. When we think of a typical ecosystem, the sun is usually the driving factor that all organisms depend on. But in a cave ecosystem, the sunlight is entirely absent not far beyond the entrance zone of the cave. The majority of the cave ecosystem remains in the dark where photosynthetic organisms do not exist. Instead, the cave ecosystem provides a distinctively unique environment is reliant on the sun’s energy outside the ecosystem (Sarbu). Caves exhibit a unique atmosphere where the organisms have become uniquely specialized through adaptation.
The majority of cave systems on Earth are mainly found in limestone rock that is subterranean. They can also be formed by wave action which erodes rock along coastlines, such as sea caves and rockshelters. The success of cave formations rely heavily on rainfall. Most caves are the result of the solution in water in contact with soluble rock along with many other varieties of processes (CAVES). There are, what seems to be, an infinite number and variety of cave systems in the world in the tropical and temperate zones of the world. It is difficult to explain one single theory on such vast array of cave types. Édouard-Alfred Martel is considered to be the ‘father of modern speleology, study of caves. He was a pioneer of cave exploration during the late 19th/early 20th century and derived a basic cave formation theory. He stated that there are several other factors that pertain to the formation of caves: the erosional factor by water, natural folding and splitting of rock, and the uplift of rock during tectonic activity (Pinney).
The process is slow, large interconnected cave systems form in limestone exposed to weathering. Rain comes in contact with atmospheric carbon dioxide; as a result, small amounts of carbonic acid are found in the solution of rainwater. This rainwater seeps into cracks and fissures of the limestone formation, the limestone begins to dissolve the carbonic rock (limestone), due to the slightly acidic rainwater and forms caves (Waltham).
The cave environment is fairly consistent all year round. The temperature of caves are determined by the mean annual surface temperature (MAST). Organisms that successfully adapt to cave life must be able to tolerate the constant temperature, humidity, and perpetual darkness (Trajanot). The evolution of cave adapted organisms portray emphasised characteristics distinguishable different from their surface dwelling relatives. DNA studies done on cave dwelling species show that they have been isolated for millions of years from their surface dwelling relatives (Sarbu).
The cave typically contains three zones that are characterized according to location, depth, and amount of sunlight. The first zone is located near the entrance where the surface and underground environments meet. The entrance zone possesses the most amount of sunlight. Next, deeper in the cave we find the twilight zone which is between the limits of vascular plants’ roots and total darkness. Finally we arrive at the dark zone, which is beyond the transition zone, deeper within the cave (Waltham).
There are many different types of organisms that gather to caves, some more permanent than others. These cave organisms fall into three basic categories of troglobites, troglophiles, and trogloxenes. Troglobites are the category of cave dwelling organisms that are among the obligate cave dwelling species, spending the entirety of their lives living within the darkest zones of the cave. Troglophiles are considered cave lovers, depend on the cave to complete their life cycles but can also be found outside of the cave ecosystem. And trogloxenes are thought to be the ‘visitors’ of caves; mostly live in caves to hibernate or for shelter and may move freely out of the cave in search for food (Andrews).
Troglobites are extremely specialized organisms that are adapted for strict cave living. Troglobites are so specialized for cave life that they can not survive outside the cave, they are not adapted to handle the strength of the sun’s rays and normal bodily functions would not operate properly. They are among the most specialized of the cave organisms and often are distinctly different from their surface-living relatives. They are highly adapt to cave life and often have highly developed and enhanced sensory organs that may include increased hairiness, lack of eyes (due to the absence of light, optical organs are merely useless) enlarged sensory organs, and longer appendages compared to their land dwelling relatives (Cave Insects).
Troglobites are may fall under the categories of predators, detritivores, or scavengers. Terrestrial troglobitic cave arthropods organisms include varying insects, arachnids, and millipedes. The insects are the most abundant in numbers, insects make up the majority of the biomass (Schneider). Oliarus polyphemus, are among the planthoppers (cricket relative) found in caves. They possess much larger antennae and lack eyes and pigment. Beetles from the family Carabidae, Leiodidae, and Staphylinidae family are typically found in temperate caves; ground beetles are among the predators in tropical caves (Cave Insects). Arachnids consist of the second largest terrestrial cave dwelling arthropods in regards to numbers. In many tropical caves, arachnids are the primary predators of the ecosystem; such as pseudoscorpions (found in temperate and tropical caves). They feed on smaller insects such as those who belong to the subclass of Arachnida, Acari which include mites and ticks (Schneider).
Millipedes are the third most abundant arthropods by quantity, especially when found in temperate caves. The myriapods are often the dominant scavengers in the cave ecosystems feeding on organic material provided by the cave floor. Caves provide subterranean aquatic habitats that may include underground lakes, screams, perched pools of water, and aquifers. These habitats house diverse troglobitic arthropods, crustaceans being the most abundant. Crustaceans account for about 2700 species adapted to troglobitic lifestyles (Pinney).
Troglophiles are cave dwellers that seem to be equally adapt to living and finding food inside and outside the cave ecosystem. Diptera, flies, are dominant trophiles in both tropical and temperate cave systems. Some cave dwelling diptera species are known to be blind and flightless, mainly found within the twilight zone. Organisms that belong to this group are among the cave cricket, millepedes, psuedoscorpions, and spiders (Sarbu).
The trogloxene group is the type of cave dwellers that more or less visit the cave. They often typically seek out caves for shelter or hibernation. This group may require the cave for a portion of its lifecycle and leave the caves in search for food. The trogloxenes include a wide variety of different organisms such as bats, reptiles, birds, and mammals (Pinney).
Food and nutrients may enter the cave either from natural forces such as different water means (percolating rainwater, sinking streams, percolating rainwater), the trogloxene group that venture outside the cave for food, animals blundering into caves, and deeply penetrating plant roots. Plants growing on barren rocky substrates of limestone must often send their roots deep into crevices within the depths of the cave to obtain water and nutrients. This occurs mainly in tropical cave regions due to the continuous growing seasons’ need for water, evaporation is high and water is found in the deeper depths of the cave (Waltham).
The trogloxene group are among the main providers of nutrients for the cave ecosystem. The successfulness of the troglobites’ rely solely on the trogloxene group to bring in nutrients from the outside world. Bat species thrive and occupy almost every cave in the world. They are social creatures that live in large colonies within the cave system. The Ney Cavern in Texas is estimated to house over 20 million bats. Bats are adapted for their activities conducted in the dark, they navigate through the dark with advanced eco-location. They remain within the cave during the day, and at dusk, leave the cave in search for food. At night, bats fly beyond the cave in search for food. The suborder microchiroptera are among the insect eaters, and the suborder megachiroptera are among the fruit eating bat species (Waltham). Bat guano, fungi, minute organic material (seeping from the surface), and microscopic organisms are what make up the base of the food chain in cave ecosystems. Troglobites found on the cave floors wait for nutrients to drop from above and are able to survive complete their life cycles according to nutrient supply (Schneider).
Typically, the bottom of the food chain in the typical ecosystems around the world come from plant life. The perpetual darkness of the cave ecosystem provides no energy for photosynthetic processes and therefore cannot produce food and nutrients on their own. The energy that is used by the cave dwellers is dependent on the surplus energy of the outside ecosystem beyond the cave for use in productivity and successful life cycles. Abundant food supplies will exhibit an increase of primary productivity, increase consumer rate of growth, and increased biomass in both aquatic and terrestrial cave ecosystems. All of which depend on the surplus of outside resources beyond the cave (Kane). The reliability of food is restricted due to the perpetual darkness and absence of green vegetation. The availability of food supply must be abundant enough to support all the numerous variety of different types of cave adapted organisms.
Cave Food Chain
(Waltham)
Caves of the World
(Waltham)
Vertical Structure of Caves
Literature Cited
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experiment." Ecological Society of America. 93. (2011): 765–776. Print.
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