Bioclimatic and geologic factors governing the evolution and distribution of Hawaiian cave insects

Highly specialized obligatory cave Arthropoda (troglobites) live in the relatively young lava tubes in the Hawaiian islands. They evolved from representatives of the speciating native fauna by the process of adaptive shifts, much like other animals have adapted to exploit novel habitats. Many Hawaiian troglobites have preadapted close surface relatives still extant and are not relicts. The deep cave zone is seen as a rigorous or harsh environment that is perpetually dark, with a relatively constant temperature, with a water-saturated atmosphere, and without many of the temporal environmental cues used by the surface species. Also, the ecosystem often appears food limited. Only a few native animals were preadapted to exploit it. The most critical environmental factor determining the distribution of troglobites within inhabitable caves is the stable saturated atmosphere. Young basaltic lava has numerous voids such as vesicles, fissures, layers, and smaller tubes which allow intercave and interlava-flow dispersal of troglobites. In fact, the largest population of troglobites are believed to inhabit these voids, and only where food and environment allow, do they enter and colonize the larger cave passages