The effect of manipulated shading on the colony abundance of two species of ants, Formica aserva and Leptothorax muscorum, in dead wood

摘要

Ants (Hymenoptera: Formicidae) are known to be a thermophilic group with fewer species at higher latitudes. They are ubiquitous in the sub-boreal forests of west-central British Columbia (Canada) in the early seral ages of forest succession, nesting almost exclusively in woody debris. Individual species begin to disappear with advancing seral ages as the canopy closes, suggesting the hypothesis that heat gain from insolation is critical to many species. We experimentally manipulated shading of two wood-nesting ant species Leptothorax muscorum (Nylander) and Formica aserva Forel to emulate advancing seral age, in an environment documented to support their normal habitation. Shaded down woody debris (DWD) was found to be ca. 2 degrees C cooler than unshaded DWD, whereas stumps were ca. 1.5 degrees C cooler when shaded than when unshaded. We found significantly fewer colonies of both L. muscorum and F. aserva in shaded wood, as compared to unshaded, in a pattern consistent with how each species has been observed to respond to advancing seral age. Temperature monitoring during the experiment indicated that soil was cooler than either stumps or DWD, possibly explaining the absence of soil-nesting ant species in these forests. The species-specific differences in ant colony abundance in response to small temperature differences, found in this study, support other research on the significance of temperature in structuring ant assemblages.