From logs to landscapes: Determining the scale of ecological processes affecting the incidence of a saproxylic beetle
Abstract
1. Species incidence is influenced by environmental and intrinsic factors operating at multiple scales. The incidence of a dispersal-limited beetle, Odontotaenius disjunctus (Coleoptera: Passalidae), was surveyed within hierarchically nested organisational levels of its environment (log sections < logs < 10-m radius subplots < 0.66-ha plots) in Louisiana, U.S.A. The finest level was the size of a single territory. Passalid beetles are an ecologically prominent group, but little is known of the factors affecting their incidence. 2. Three scale-sensitive aspects of O. disjunctus incidence were evaluated: (i) the extent (52-3600 ha) within which forest cover was most associated with incidence; (ii) the hierarchical level at which environmental variables best predicted incidence; and (iii) the hierarchical level at which incidence exhibited the greatest spatial autocorrelation as a result of intrinsic factors (e.g. dispersal limitation). 3. Forest cover best predicted incidence at 225 ha, but accounted for only 1.2% of variation in incidence. Incidence was most sensitive to environmental factors measured at the finest scale (i.e. territories). Incidence was positively associated with moderately decayed wood and increased surface area of logs (9.9% and 3.1% of variance, respectively). When environmental factors were accounted for, spatial autocorrelation in incidence was greatest within subplots and logs, consistent with the hypothesis that intrinsic autocorrelation is associated with O. disjunctus average dispersal distance (<5 m). 4. This study indicates the influences of factors acting at multiple scales, but suggests that environmental conditions at the scale of territories may be most important for species incidence. © 2012 The Authors. Ecological Entomology © 2012 The Royal Entomological Society.