Nutrient Cycle of an Isolated Cave

Introduction

The caves are simple natural laboratories. The climate of the cave is very stable and easy to define. Cave environment is composed with a twilight part close to the entrance, a middle part of full darkness and unstable temperature, finally a part of full darkness and stable temperature in deeper. The twilight part is the biggest and most diverse fauna container. The middle part contains some common species which can move to the earth. The deeper dark sides, which are the unique aspect of the cave environment and contain obligate (trolobitic) fauna. Green plant can’t live in stable darkness. So, the food reserve here in other forms (Poulson and White, 1969). Animal communities in the caves look remarkable chances for the investigation of community dynamics because of their relative simplicity. A comparatively small number of species is involved in even in most complex cave community but exceptionally large numbers of colonies of bats are present here. In absence of light, primary producers are absent or at least limited to chemosynthetic autotrophs. Sulfur and iron bacteria are present in some caves but their quantitative significance as producers has not yet been established (Barr Jr, 1967). The superficial nutritive part of cave clay in the blind amphipods of the genus Niphargus show that juvenile stages burrow widely and probably eat the clay in the bottom of cave pools. Presumably the juveniles utilize the bacterial content of the clay rather than the mineral material itself; and in any case, continued survival of the adults is dependent upon the presence of additional food (Barr Jr, 1967). In addition to absence of light, the physical environment of a cave is characterized by silence, relatively constant temperature which approximates the mean annual temperature of the region where the cave is located, high relative humidity except near entrances, is accompanied by an exceptionally low rate of evaporation (Barr Jr, 1967).

Cave Habitats and Ecology

Different types of caves contain variety of habitats within them and differ in amount and types of energy level. Cave supports heterotrophic microbial populations in the presence of huge input of organic carbon, nitrogen and phosphorus due to accumulation of guano and dead bats, if a cave has substantial or modest populations of bats (Cheeptham, 2012). Guano is a organic deposit common in cave derived from mainly feces of a variety of animals specially bats that visit or live and provide habitat rich in nitrogen, carbon and phosphorus that’s are nutrients for many insects (Cheeptham, 2012; IUCNSSC, 2014). Ecological classification of cavernicoles was first prepared by (Schiner, 1853)and improved and promoted by (Racovitza, 1907).They splits them into (1) troglobites, which are obligate species to the cave; (2) troglophiles, which live and reproduce not only in caves but also in cool, dark, moist microhabitats outside of caves they termed as facultative species; (3) trogloxenes, species those use caves for shelter throughout the day but feed outdoor at night; and (4) cave accidentals, which Confused with those species that certain small troglobites are also phreatobites (Barr Jr, 1967).

Figure-Different zones of a cave

The major energy sources of cave ecosystems are (a) organic matter flounced underground by sinking streams, and (b) the feces, eggs, and dead bodies of animals those are persist in the cave for shelter but feed outside (trogloxenes). In temperate region caves flooding and the entering of cold air throughout winter and initial spring interrupt the comparatively constant physical conditions of the cave environment (Barr Jr, 1967). The security of roosting sites is a vital element of any policy for the conservation of bats. Since caves are the foremost roosts for numerous bat species (Dalquest and Walton, 1970; Kunz, 1982). There are various types of bat species and large number of bats found in different cave, Seventeen species of bats roost in the caves of Yucatan, Mexico. The conservation of these types of sites should be of principal attention for the protection of chiropteran species (Arita, 1996).

Cave communities

Connectivity among communities is continued by the rearrangement of biomass, frequently by mobile animals that eat resources in one habitat and then reproduce, urinate, and/or defecate in other surroundings. This transmission of organic material affects the nutrient budget of a community and effects population and food web dynamics (Emerson and Roark, 2007). Cave-roosting species spent half of their lives inside the caves (Kunz, 1982). The security of cave atmospheres is essential to guarantee their conservation. In a parallel fashion, the presence of bats might be an essential state for the existence of cave environments. In channels with no bats, biomass thickness in a typical North American cave can be as little as 1 g/ha in ponds or 20-30 g/ha in terrestrial zones (Poulson and White, 1969). In contrast, passageways covered with bat guano present an excess of nutrients and provide very diverse groups of arthropods (Barr Jr, 1968; Harris, 1970; Poulson, 1972). For endogenous primary manufacture by chemosynthetic bacteria is insignificant, cave communities depend completely on exogenous origins of nutrients for their maintenance (Culver, 1982).

Figure-Cave communities and feeding cycle

Nutrients can be occupied into a cave in the form of detritus and plant material passed by watercourses, as dissolved organic matter infiltrating through minute cracks or exuding from tree roots (Howarth, 1972; Howarth, 1983), otherwise they can be placed inside caves as feces of trogloxenes, for example cave crickets, bats, birds, and other animals (Harris, 1970; Poulson, 1972; Culver, 1982). In various tropical caves, bat guano is by far the most significant source of nutrients. By carrying tons of organic matter to the caves, bats act as transferable links concerning cave environments with the external world (Arita, 1996). Any animal existing in a cave can be said as a cavernicole. Troglobites, which are obligate cavernicoles, are the emphasis of this appraisal. Many troglobites are offspring of troglophiles. Facultative cave populations are able to alive in or outside caves. Trogloxenes are consistent cave inhabitants that return intermittently to the exterior for food; bats and cave-crickets are examples. Main taxonomic collections of animals with various troglobitic species comprise collembolans, turbellarians, millipedes, spiders, pseudoscorpions, gastropods opilionidsisopods, amphipods, diplurans, decapods, beetles (Pselaphidae, Carabidae, Leiodidae), salamanders and fishes.(Barr and Holsinger, 1985)

Cave Nutrient Cycle

Food contribution into a cave ecosystem is attributable to two chief sources- sinking watercourses, which wash twigs, logs, bacteria, leaves and epigean animals (including zooplankton) into caves; and trogloxenes, which deposit their eggs and feces in caves and frequently die there and donate their bodies to the ecosystem (Barr Jr, 1967). Species from exterior sources include the bulk of the plankton in the Cave (Scott, 1909) and rivers inside Cave (Kofoid, 1899). Smaller individuals of the blind cavefish, Amblyopsis spelaea, feed mainly on copepods in this plankton (Poulson, 1963). Plant fragments are placed along the banks of subterranean streams, where they are gradually decomposed by bacteria and fungi. The decomposers provide food for detritus-feeding animals (e.g., diplurans, milli-pedes, and collembolans) which are then eaten by predators (e.g., opilionids, spiders, carabid beetles, pseudoscorpions). Bats and the eastern cave crickets of the genus Hadenoecus (Park and Barr, 1961) are important guano manufacturers in caves of the United States. Few troglobites are able to use the guano directly, while guano is usually populated by a characteristic assemblage of troglophiles which may be eaten by predatory troglobites (Jeannel, 1949). Seasonal differences in the physical atmosphere and food supply of temperate zone caves are often unexpectedly drastic. During late winter and spring overflowing of rivers Cave, typically raises the water level 5 or 6 m, and a maximum rise of nearly 15 m has been recorded. Additionally the flood is a drop in temperature of the water and small increases in pH, entire alkalinity, and dissolved oxygen (Barr Jr, 1967). A much longer existence time in a riparian species of cave beetle when the riparian species and another species usually found in drier, higher cave galleries were immersed in water. Many species of Pseudanophthalmus and Ameroduvalius (troglobitic Carabidae) normally feed on little tubificid annelids in the damp silt along cave streams (Barr Jr and Peck, 1965). The effects of flooding on aquatic cavernicoles, suggesting that spring floods may trigger their reproductive cycles (Poulson, 1964). Winter poses additional hazards for terrestrial troglobites. Food supplies vary seasonally in caves. Guano deposition by bats is limited to summer months, and Hadenoecus spp. feed outside the caves less often throughout winter than in summer, so there is minimum guano supply in winter. Conversely, deposition of organic detritus by watercourses is improved in winter because of flooding, but decomposition of the fragments takes place gradually over the time of several months or years. A great plankton count in Echo River of Mammoth Cave occurs only throughout late spring or summer floods, when plankton manufacture in Green River, which provides the flood waters, is great (Barr Jr, 1967). The genus Pseudanophthalmus covers about 175 species (many of them not yet described) and is known from Indiana, Kentucky, Illinois and Tennessee, Alabama, Georgia Virginia, West Virginia, Pennsylvania, and Ohio (Barr Jr and Peck, 1965). Ameroduvalius, limited to south- east Kentucky, has only three species; Nelsonites, from the Cumberland Plateau of Tennessee and Kentucky, has two; and Neaphaenops and Darlingtonea, from many parts of Kentucky, are monobasic. All of these beetles are predatory troglobites and are supposed to be remnants of a well-known soil-and-moss-dwelling periglacial fauna (Barr Jr, 1965).

Figure- The cave food pyramid

Guano

Bat guano supports an accumulation of organisms that differs depending on the species of bat manufacturing it. Alterations in guano composition propose that guano from bats in unlike feeding guilds can affect ecosystem configuration and dynamics differently (Emerson and Roark, 2007). Allochthonous effort of nutrients such as nitrogen and phosphorus, which are found in comparatively high concentrations in bird guano, increases primary productivity in terrestrial ecosystems by improving the quality and quantity of vegetation (Polis et al., 1997). Nutrient input through guano deposition by seabirds has also been shown to increase the abundance of organisms such as detritivorous beetles on islands used by roosting seabirds (Sánchez-Piñero and Polis, 2000). In addition to its effects on primary and secondary productivity, allochthonous nutrient input can also influence community structure the presence of birds and nutrient-rich guano significantly alters the structure of intertidal communities by enhancing algal growth and settlement of invertebrates in dense algalmats (Bosman and Hockey, 1986). Such consumer-driven nutrient recycling via fecal deposition by bats also affects community structure in guano-based ecosystems. Bat guano forms the basis of a food web consisting of bacteria, fungi, protozoans, nematodes, and arthropods (Harris, 1970). Cave salamanders consume guano of grey bats (Myotis grisescens) and incorporate the nutrients they obtain through coprophagy into body tissues (Fenolio et al., 2006). The diversity of organisms associated with guano has been shown to vary depending on the diet of the bat producing it, with guano of sanguivorous, insectivorous, and frugivorous bats supporting different assemblages of invertebrates (Ferreira and Martins, 1998). Differences in guano composition (C, N,P, and mass ratios) most likely resulted from dissimilarities in nutrient composition of the diets of each bat species (Studier et al., 1994). Variation in nutrients and stoichiometric nutrient ratios of guano from bats in different feeding guilds could have considerable effects on producers, consumers, and decomposers living on or in guano.

Figure- Collection of guano from cave

As highlighted by (Sterner and Elser, 2002) and subsequently in reviews by (Vrede et al., 2004) and (Moe et al., 2005), relationships among elemental nutrients have the potential to regulate processes at many ecological levels, including production, individual and population growth, coexistence of species, rates of decomposition of organic matter, and nutrient cycling. Primary production in terrestrial ecosystems (as in marine systems) is thought to be limited by the availability of N and P (Vitousek and Howarth, 1991), and the input of these nutrients by fecal deposition can have considerable bottom-up influences in detritus-based ecosystems. Ecosystem-level effects of different nutrient contents could also result from differences in rates of conversion of nutrients in guano from biologically unavailable to available forms (Vitousek et al., 1988). Differences in guano nutrient profiles could have considerable ecological consequences ranging from effects on the growth or productivity of individual residents of guano piles to effects on ecosystem-level processes like decomposition and nutrient cycling (Emerson and Roark, 2007).

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