Connections between individual dispersal behavior and the multi-scale distribution of a saproxylic beetle
Species incidence results from a complex interaction among species traits (e.g., mobility and behavior), intra- and inter-specific interactions, quality and configuration of the landscape, and historical events. Determining which factors are most important to incidence is difficult because the multiple processes affecting incidence operate at different temporal and spatial scales. I conducted an empirically-based study relating individual behavior (dispersal, habitat selection, and intra-specific interactions) with hierarchically-organized environmental filters to predict the incidence of Odontotaenius disjunctus (Passalidae), a saproxylic (=decayed wood dependent) beetle common to eastern North American forests, at multiple spatial scales. In dispersal experiments, O. disjunctus movement was faster and more linear in suitable habitat than in unsuitable matrix (non-forest), and O. disjunctus exhibited a strong response to a high-contrast boundary between forest and open-field. A hierarchically-organized (log-section < log < subplot < forest plot) survey of incidence across 22 forest plots in Louisiana showed that patchiness in incidence was greatest at fine-scales (log-section and log), partly in relation to two environmental variables: decay state and log surface area. In fine-scale habitat selection experiments, resettlement distances were usually less than 5-10 meters, and immigration was positively influenced by log size and the presence of conspecifics, although aggregation associated with conspecific attraction did not occur because emigration balanced immigration. Additionally, population growth rate showed negative density dependence in post-settlement experiments. Finally, I developed an individual-based, spatially-explicit simulation model to relate fine-scale response to cues (habitat, mate, and conspecific density) and dispersal limitation to the density-area relationship. Unlike conspecific search, mate search did not result in large aggregations of individuals on large patches, but instead resulted in almost even density among patches. Both habitat and mate search led to high overall incidence even when dispersal limitation was high. I conclude that O. disjunctus is a low-mobility species for which incidence is primarily determined by fine-scale interactions with conspecifics and the environment, and for whom high incidence can be explained in part by efficient use of cues during habitat search. Although sensitivity to large-scale habitat loss is a consistent pattern across taxa, this study emphasizes the overriding importance of fine-scale processes in predicting incidence.
reproduction, social information, phenotype evolution, fitness consequences, habitat fragmentation, breeding dispersal, spatial scale, individual-based model, natal dispersal, ecology
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