DENSITY-DEPENDENCE DEPENDS ON SCALE - AT LARVAL RESOURCE PATCH AND AT WHOLE POPULATION

A previous study (Tuda and Shimada, 1993) has shown that the equilibrium population size of the azuki bean beetle was lower at 32-degrees-C than at 30-degrees-C and that this difference was due to a reduced maximum population size of emerged progeny through inside-bean process. In this paper, these results were analyzed further on the scale of the individual bean where interaction among larvae took place. Per-bean numbers of deposited eggs, hatched eggs, and emerged adults have been recorded at seven different parental densities under the two temperature conditions. Three individual-bean-scale process hypotheses that may explain the reduced maximum emergence density on the whole population scale are suggested: (1) a lower maximum emergence per bean at 32-degrees-C than at 30-degrees-C, if the bean scale and the whole-population scale share the same density-dependent pattern in adult emergence, (2) a limited range of hatched egg number per bean at 32-degrees-C, resulting from the adult oviposition process outside beans, and (3) different patterns of density-dependent emergence between the two different scales. This study showed that the inside-bean pattern of responses on the bean scale was a simple saturated curve at 30-degrees-C, but one with a discontinuous decline at higher hatched egg densities at 32-degrees-C. On the contrary, during outside-bean process, the peak number of hatched eggs decreased on this scale as observed on the whole-population scale. I discuss why the extracted factor of inside-bean process on the whole-population in the previous study could not be applied to the bean-scale pattern.