Conservation Theory and Management | Cave Formation and the Ecosystem Within | By: Robert Luncsford |

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The formation of a cave begins when rainwater falling through the atmosphere absorbs carbon dioxide causing it to become acidic. The rainwater then passes through the soil collecting more carbon dioxide from dead plant life and animals. The acidity allows the rainwater to chemically react to limestone or dolomite rock which starts the formation of caves through a process called chemical erosion. Physical erosion then takes place as the cave becomes larger and water flows through it washing away rocks and sand, and after thousands or even millions of years large caves are formed. There are four main types of cave classifications, since not all caves are formed through that one process, the process mentioned above forms what is known as a Solution Cave. Lava Caves are another type that is formed when the outer surface of a lava flow cools while the molten lava within continues to flow and eventually flow out. Sea caves are formed by waves eroding away the shores of large lakes and oceans. Glacier caves are the last main type of cave which is formed by melt water that causes drainage tunnels through the glacier. On our last forestry management class field trip we visited a solution cave that formed just west of Licking Missouri. During our trip we observed many interesting sights and types of wildlife who had formed their own ecosystem completely separate from the outside world. There are a few ways to look at cave biology and ecology such as the ecosystem approach. In general, an ecosystem consists of biotic and abiotic elements interacting, while energy flows and nutrients cycle through the system. A cave is a low ordered system, in other words, it’s pretty simple. First of all, caves lack the producer (or first trophic) level because there is no plant life. Systems on the surface are usually diverse and complex, and therefore stable. Caves, on the other hand, have low stability and are vulnerable to disturbance. As for food chains, caves have a Detritus Food Chain, not a Grazing Chain, like the outside worlds food chain. The pathway from the base of the web is the breakdown of organic material, not plant-grazing. “Energy is limited in caves; it comes second hand from the surface, through a relatively small quantity of detritus (dead organic material or feces). The conversion of energy from one level to the next is inefficient. Whereas most surface ecosystems convert energy at roughly a 10 percent rate (for example, from plant to herbivore to carnivore), in caves the conversion rate is about 2.5 percent.” (Cave biology, online quote) In a nutshell, a cave ecosystem is characterized by ecological simplicity, scarcity of energy (food), and climatic stability.
When looking at a typical trophic web in a cave, at the first level are autotrophs, which can take inorganic raw materials and "build" an organic body. Outside of caves, plants (through the process of photosynthesis) are a great example of autotrophs. Near cave entrances, where sunlight still reaches, moss, ferns, and algae can grow. Deep in the cave, however, a process called chemosynthesis is the only way to go. Bacteria may, for example, convert clay minerals and use the resulting release of energy. These "chemotrophic" bacteria may not be the most obvious cave organisms, but they are the most common. “Chemotrophic iron bacteria (Perabacterium spelei) can take carbon and iron carbonate from cave walls, and nitrogen from the air, and live off the conversion to ferrous oxide. Sulfur bacteria are present in caves with pyrite and other sulfide minerals. Nitrosomonas and Nitrobacter are two bacteria that decompose nitrogenous organicmatter. It is likely that the nitrate of saltpeter derives from these bacteria breaking down the urine of the pack rat, which leaves a urine trail to help it navigate between the cave and surface.” (Cave biology, online quote) At the next level, all these chemotrophs may be food for flatworms, or isopods. Detritus (bat guano, other feces and dead organisms) become food for animals such as other bacteria, fungi, flies, beetles, gnats, hellgramites, crustaceans, millipedes, mollusks, and certain types of worms. The cave we visited on our trip had an ample supply of guano, thanks to the pipistrelle bats we seen, providing plenty of food for the gnats and fungi I observed while in the cave. Above that, a cave may have spiders, pseudoscorpions, predatory beetles, planaria, crayfish, cavefish, frogs, or salamanders. I was fortunate enough to observe cave spiders, and salamanders on our trip although I’m very confident that with more time and better lighting I may have been able to find some cave frogs, since the conditions seemed perfect for them in the cave. “In the near surface-like conditions at the cave entrance, snails and harvestmen, and carnivorous web worm larvae may thrive. Ferns and moss grow at the cave drip line in the cool, moist conditions (which represent glacial relict conditions). Black rat snakes may use the coolness of the entrance and also find prey”, (Cave Biology, Online Quote) although I did not observe any snails, ferns, moss or snakes in this certain cave entrance.
Cave organisms can be placed in three categories: troglobites, troglophiles, and trogloxenes. Troglobites are "obligative cavernicoles"--they can live only in caves. Often in these creatures we see a regression of pigment and photoreceptors, longer and more slender appendages, ultra-sensitive sensory structures, less fecundity, and larger yokes in egg-layers. Contrary to what many people think, troglobites are only a small percentage of cave fauna. Troglophiles may complete their life cycles in a cave, but are not confined there. On the surface, these animals may occur in habitats similar to caves, in sheltered, cool, and moist places. Trogloxenes spend only part of their life cycles in caves. A fourth category is accidentals that may wander, fall, or be washed into caves. “DNR cave biologist Bill Elliott reported in 1999 that Missouri has about 21 species of terrestrial troglobites and about 40 species of stygobites (aquatic troglobites)." (Cave study at Fisher cave in Missouri, online quote) The limiting factors of food, temperature, and humidity select which organisms can live successfully in a certain cave. Troglobites need little food, and in fact would be outcompeted for food if there were suddenly an abundance of it. Troglobite physiology means these creatures get by at a very low metabolic rate and are not required to keep their internal temperatures high. Some animals also rely on high relative humidity. Salamanders, like the cave salamanders we seen on our trip, need humid air to keep their skin moist for breathing. In caves, nutrients enter in a limited number of ways such as deposits of bat feces (which was bountiful in this cave), dead bodies of animals, wind-blown particles, rainwater (which was also visible in the cave) floods, and even cavers. I believe that the main reason life is able to exist in the cave we visited is due to the guano from the pipistrelle bats that occupy the cave year round, and also the little brown and big brown bats that are there seasonally. Without them (and their feces), there would not be enough non-living organic material (Detritus) for other organisms to survive and thrive inside the cave ecosystem.