A functional classification of interstitial invertebrates: supplementing measures of biodiversity using species traits and habitat affinities

Although functional classifications have been successfully used in terrestr ial and marine ecosystems to generate ecological hypotheses, compare local and regional environments, and supplement studies of biodiversity, they rar ely have been applied to aquatic ecosystems, especially interstitial ones. We present two complementary classifications of interstitial invertebrates, and demonstrate their utility as a supplement for conventional measurement s of biodiversity, as "common currency" for regional and global comparisons , as a tool for generating hypotheses, and as indictors of ecological varia tion in space and time. The first classification uses three species traits: diet, locomotion, and body size. Although mode of reproduction and extent of parental care were originally explored, these traits were less useful fo r prediction and explanation. The second classification reflects the degree of affinity for different subsurface habitats. Invertebrates can be classi fied as stygoxenes, stygophiles and stygobites. Changes in conditions in su bsurface habitats (e.g. through groundwater extraction, sedimentation) can alter the proportions of these categories, providing a useful biological in dicator of subsurface dynamics. Presently, use of these functional classifi cations is limited by a lack of autecological data for many interstitial sp ecies. However, as our knowledge increases and these data are obtained, the re is great potential for large-scale ecological hypothesis-testing, predic tion of the effects of human and natural disturbances, and global compariso ns of interstitial assemblages and biodiversity.