Cave Life — Nicholaus Vieira

Subterranean life forms are classified according to how dependent they are on the underground environment.

Troglobites – Are cave adapted organisms that cannot survive on the surface, and must spend their entire lives in caves. They have adapted to survive and exploit their stable environment, some adaptations include:

· Loss of pigmentation

· Reduction and sometimes complete loss of eyes

· Extension of sensory structures

· Elongation of locomotory spines and claws

· Reduced size

· Changes to circadian rhythms

· Changes to reproductive biology and life cycle

Not all troglobite species are restricted to single areas of contiguous karst. On average aquatic troglobites have a greater range than their terrestrial counterparts. There are no troglobitic mammals.

Troglophiles – Can spend their entire life in caves, but also occur in similar dark, damp-surface environments. ie. salamanders, crickets etc.

Trogloxenes – Organisms that use caves for some portion of their life-cycle, but also spend part of their time on the surface. ie. bats, harvestmen etc.

Stygobites, Stygophiles, Stygoxenes – Aquatic varieties of troglobites, troglophiles, and trogloxenes.

Accidentals – “Critters” that have fallen, washed, and/or wandered into caves, that can live but will not become established. ie. frogs etc.

Extremophiles – This term refers to organisms that have adapted to conditions such as temperature, pH, or the mixture of atmospheric gasses that fall outside what we humans consider the normal range. Not necessarily strickly cave dwelling organisms, they are often microbes.

How did these troglobites evolve to live underground?

Pleistocene-effect theory – suggests that climatic changes during the Pleistocene rendered surface habitats unsuitable for the surface dwelling counterparts of troglophile populations and isolated the troglophiles in subterranean refugia. Isolation fueled speciation, as the troglophiles evolved into troglobites. By the time climatic conditions on the surface improved, the former troglophiles had become so specialized as subterranean life forms that they could no longer exist on the surface. This is the most widely accepted theory in temperate latitudes.

Adaptive shift theory – Does not involve isolation due to climatic changes, but proposes that the partly adapted ancestors shifted into newly developed food niches (increased specialization allowed the exploitation of new habitats) where there was less competition. So, their evolution is continual, rather than episodic as implied by the Pleistocene-effect model.

The theories are not mutually exclusive, and both may have played a role in the evolution of troglobites.