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Life
inside the caves
According to Frank Howarth, stresses in a cave environment include, “perpetual
darkness and humidity, lack of important environmental cues, complex mazelike
living space, stressful or even lethal gas mixtures, patchy food resources,
barren rocky substrates, wet and slippery vertical surfaces, and occasional
flooding.” (1993: S65). Despite these barriers, there are still
organisms present inside the Moiliili Water Cave. Some recent cave exploration
observed blind catfish and blind spiders, while blind mullet and blind
gambusia were located in nearby ponds (Lao: pers comm.). Lao thinks that
the underground fish first came from a surface source, and then adapted
to the dark environment (Watanabe 1996). Other organisms present include
freshwater golby, small snails, and a millipede (pers observation).
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The main factor
attributed to the adaptation of cave species is stress. Stress is defined
by Frank Howarth (1993: S65) as: “an environmental parameter that
causes a potentially injurious change in a biological system,” and
causes: “an increase in mutation and recombination rates as well
as other changes in the genome.” Cave adapted species usually share
such features as “reduced or absent eyes and bodily pigments, elongate
appendages and body form, flightlessness or otherwise reduced dispersal
powers, and often more numerous and enlarged sensory structures.”
(Howarth 1993: S66). Mutation rate increases by the distressing of the
genome of small founder populations by the selection pressures in the
cave. This causes the adapted population to emerge quicker than under
less stressful conditions (Howarth 1993).
The
primary food resources in caves include organic substances that are brought
inside by water and gravity. As William Halliday (pers. comm.) observed,
the fish inside the (Moiliili) cave were eating something that dripped
from a dribble of water. He also noted that “biota is concentrated
near the entrance. Large and small roots are present, with mycelia present
on some” (Halliday 1994).
Other food resources include, plant roots and accidentals. Plant roots
(fig. 4) tunnel deep into the earth in search of water. In some caves,
food energy may be derived from the chemoautotrophic bacteria found with
such roots (Howarth 1993). Accidentals are organisms that enter into or
fall into caves accidentally. These organisms are not suited for cave
life and become food for other organisms (Howarth 1993).
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