Competition and niche separation between two bark beetles: existence and mechanisms [Ips duplicatus]

• Published in: Oikos Vol. 68; no. 3; pp. 437 - 447
• Main Authors: Schlyter, F, Anderbrant, O. (Lund Univ. (Sweden). Dept. of Ecology)
• Format: Journal Article
• Language: English
• Published: Oxford Munksgaard International Publishers, Ltd 01-12-1993; Blackwell
• Subjects: Animal and plant ecology; ANIMAL POPULATION; Animal, plant and microbial ecology; Bark beetles; Biologi; Biological and medical sciences; BIOLOGICAL COMPETITION; Biological Sciences; BIOTA; BIOTE; Coleoptera; COMPETENCIA BIOLOGICA; COMPETITION BIOLOGIQUE; DENSIDAD DE LA POBLACION; DENSITE DE POPULATION; Density; Ecological competition; Ecology; Ekologi; ESTRUCTURA DE LA POBLACION; EVOLUCION DE LA POBLACION; EVOLUTION DE LA POPULATION; Female animals; Fundamental and applied biological sciences. Psychology; HABITAT; HABITATS; Invertebrates; IPS TYPOGRAPHUS; Male animals; Natural Sciences; Naturvetenskap; NORUEGA; NORVEGE; NORWAY; PESTS OF PLANTS; Pheromones; PICEA ABIES; PLAGAS DE PLANTAS; POBLACION ANIMAL; POPULATION ANIMALE; POPULATION CHANGE; POPULATION DENSITY; POPULATION STRUCTURE; RAVAGEUR DES PLANTES; Species; STRUCTURE DE LA POPULATION; Synecology; Terrestrial ecosystems; Trees; Chemical communication; Competitive exclusion; Coleoptera; Insecta; Pest; Phloem; Arthropoda; Gymnospermae; Softwood forest tree; Interspecific competition; Ecological segregation; Competitive feeding; Niche; Coniferales; Spermatophyta; Density dependence; Aggregation pheromone; Invertebrata; Picea abies; Ips typographus; Scolytidae
• ISSN: 0030-1299; 1600-0706
• DOI: 10.2307/3544911

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, population phases), in the same substratum in the laboratory, there was a strong, asymmetric larval competition in favour of Ips typographus. The larger species had a higher reproductive rate in all eight density combinations where the species were reared together. Thus, an adult individual of I. duplicatus would benefit most if it could avoid breeding closely together with I. typographus. Mean offspring body mass decreased for both species as inter- or intraspecific density increased. This resource partitioning between the individuals indicate that the larval competition was of the 'scramble' type. This conclusion is supported by a near complete consumption of the larval food (phloem) and similar egg-laying times (adult re-emergence dates). When the two species were bred separately the two reproductive rates were similar. There were small differences in breeding performance in the laboratory on logs with a diameter between 5 and 15 cm. When given a choice there was a preference by adults of the larger species for larger logs. A clear separation in the aggregation pheromone signal is now known, which allows most colonizing individuals of the smaller species, except the pioneering males, to orient and land on areas outside the range of the larger, supreme competitor.