Competition and Niche Separation between Two Bark Beetles: Existence and Mechanisms

The existence and effects of competition as well as niche separation were investigated in a system of two bark beetle species which aggregate on Norway spruce, Picea abies, to feed on and reproduce in the phloem. In this and other bark beetle systems, there is evidence for competition and intra- and interspecific density effects at normally occurring densities, in contrast to the concept of «density vagueness». Under natural conditions adults of the two species showed a spatial niche separation, where the smaller species, Ips duplicatus, occupied only the top of trees. Regression analysis of adult density patterns of each species showed effects of habitat variables and of density of the opposite species. When breeding at naturally occurring densities (representing both low, endemic, and high, epidemic, populations phases), in the same substratum in the laboratory, there was a strong, asymmetric larval competition in favour of Ips typographus