Jackson, H. B., K. Baum, A. Zeccarias* and J. T. Cronin. 2012. From logs to landscapes: Determining the scale of ecological processes affecting the incidence of a saproxylic beetle.Ecological Entomology 37(3): 233-243
ABSTRACT
1. Species incidence is influenced by environmental and intrinsic factors operating at multiple scales. We surveyed the incidence of a dispersal-limited beetle, Odontotaenius disjunctus (Passalidae), within hierarchically nested organizational levels of its environment (log-sections < logs < 10 m radius subplots < 0.66 ha plots) in Louisiana, USA. Passalid beetles are a diverse and ecologically prominent group, but little is known of the factors affecting their incidence.
2. We evaluated three scale-sensitive aspects of O. disjunctus incidence and its relationship to environmental and intrinsic factors: 1) the extent within which forest cover was most associated with incidence in log-sections (52-3600 ha); 2) the hierarchical level at which environmental variables best predicted incidence; and 3) the hierarchical level at which O. disjunctus exhibited the greatest autocorrelation due to 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. Instead, incidence was most sensitive to environmental factors measured at the scales of daily movement (log-sections) and average dispersal (logs). Incidence was positively associated with moderately decayed wood and increased surface area of logs (9.9% and 3.1% of variance, respectively). After environmental factors were accounted for, 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 potential for fine-scale habitat structure to outweigh landscape structure when predicting incidence of dispersal-limited species.
Keywords: scale of effect; focal patch; intraclass correlation; habitat fragmentation; habitat loss; xylophagous; saproxylic; Passalidae
