The NSS Bulletin - ISSN 1090-6924
Volume 40 Number 4: 103-117 - October 1978
A publication of the National Speleological Society

An Evolutionary and Ecological Analysis of the Terrestrial Arthropods of Caves in the Central Pyrenees
Kenneth Christiansen and Michel Bullion

Abstract

Part 1: Ecological Analysis with Special Reference to Collembola

Although caves present a wide variety of habitat types, the arthropods we studied suggest four basic categories: (1) cave depths (profoundeurs), (2) entrances, (3) mixed caves (where there is no entrance/profoundeur separation), and (4) underground rivers. Both sharing and partitioning of the environment occur in cave arthropods, usually involving closely related species. These processes generally appear to result from shared or differing ecological requirements.

Ecological factors associated with abundance and distribution of these species are extremely involved. The complex of critical factors varies greatly from one species to another, and there are no overall groupings of ecological important features. In spite of the relatively simple nature of the cave profoundeur environment, the governing factors appear to be generally more complex for troglobitic than for torglophilic species. Thus, diminishing the number of ecological variables does not, apparently, simplify the ecological web of relationships. It is porbably, then, that the primary factor in determining the complexity of interaction is the stability and complexity of the habitat. Thus, the cave depths would harbor the most complex interactions and the entryways the least.

Part 2: Evolutionary analysis of three species of Collembola

Three related species of cave Collembola, representing different levels of evolutionary cave adaptation, show little correlation between local ecological conditons affeting their abundance and distribution and the evolutionary status of the populations. The most highly evolved species shows a storng positive correlation between evolutionary status and both the probable date of initial colonization and the number of species in a cave. The two primitive species apparently are recent cave invaders and do not, as yet, show any clear evolutionary trends toward cave adaptation.

The most highly evolved cave species shows about twice as much intrapopulation variability as does either of the two primitive species This, as well as life cycle and apparent selective forces, points to a major shift in evolution between the two primitive and the one advanced species.

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