Factors Influencing Microhabitat Partitioning among Coexisting Species of Arid-Land Darkling Beetles (Tenebrionidae): Behavioral Responses to Vegetation Architecture

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Abstract
In the arid, sagebrush-steppe ecosystem of southwestern Wyoming, [USA], Eleodes darkling beetles partition microhabitats across a mosaic of shrub patches differing in mean shrub height and density. In this study, the functional role of behavioral responses of four species of darkling beetles to vegetation architecture was examined under both laboratory and field conditions. Behavioral data were integrated with known physiological attributes of each species to explain the observed field distributions. Laboratory tests of orientation responses of beetles to an artificial vegetation architecture (black and white silhouettes of shrubs) revealed that Eleodes constrictus and Eleodes pimelioides, which preferred cool, shrub-shaded microhabitats, approached shrub silhouettes more frequently and at lower temperatures than Eleodes extricatus, a species from a warm, more open microhabitat. Shrub orientation responses became more pronounced at higher temperatures. Eleodes nigrinus, a strictly nocturnal species that also preferred open habitats, responded to the shrub silhouettes only at high temperatures. Physiological attributes (species-specific temperature preferences and tolerance to heat stress) were associated with each species'' response intensity. In the field, a replicated, shrub architecture manipulation experiment tested for shifts in microhabitat use among the four species of beetles. Vegetation manipulation (shrub removal or addition) resulted in the virtual extirpation of E. constrictus and E. extricatus from their respective microhabitats, but not of E. pimelioides and E. nigrinus. Shrub manipulation did not result in recruitment of species to favorable microhabitats, indicating that while vegetation architecture is a critical microhabitat component, other factors are also involved in microhabitat selection by Eleodes.

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