Population ecology of carabid cave beetles

The population ecology of three species of obligate cave dwelling (i.e., troglobitic) carabid beetles, Neaphaenops tellkampfi, Pseudanophthalmus menetriesi and P. pubescens, was studied in five cave habitats in west central Kentucky. Population size, timing of teneral occurrence, sex ratio, proportion of ovigerous females and clutch size were monitored in 12 populations. The data indicate that cave carabid beetles undergo density fluctuations at the local population (subpopulation) level which are intermediate in severity to those observed in surface dwelling carabid species. However, composite populations of N. tellkampfi show overall density fluctuations which are not statistically different in severity from those of more stable surface carabid species. It appears that spatial heterogeneity has a damping effect on density fluctuations in N. tellkampfi over the geographic area studied. A similar explanation has been offered for the more stable surface carabid species.The predictable nature of the cave environment and the reduced number of selection pressures in cave habitats has permitted us to consider evolutionary patterns in these cave carabid species as they relate to differences in ecology. Two major adaptive pathways can be inferred from the population data of this study. Pseudanophthalmus menetriesi and P. pubescens appear to have undergone divergent evolution for habitat specialization in mesic and riparian habitats respectively. Significant life history differences between these two species appear to be related to the characteristics of mesic vs. riparian habitats. Neaphaenops tellkampfi is specialized to prey on cave cricket (Hadenoecus subterraneus) eggs and nymphs, resources which are highly seasonal and become rare in the fall. As a result N. tellkampfi has retained some generalist traits in feeding and in habitat utilization. Its life history characteristics are more variable than those of the Pseudanophthalmus spp. and appear to allow N. tellkampfi to exploit two distinct subniches in the depauperate cave environment.