  This paper considers the evidence that debris disks are self-stirred by the
formation of Plutos. A model for the dust produced during self-stirring is
applied to statistics for A stars. As there is no significant difference
between excesses of A-stars <50Myr old, we focus on reproducing the broad
trends, the "rise and fall" of the fraction of stars with excesses. Using a
population model, we find that the statistics and trends can be reproduced with
a self-stirring model of planetesimal belts with radii distributed between
15-120AU. Disks must have this 15AU minimum radius to show a peak in disk
fraction, rather than a monotonic decline. Populations of extended disks with
fixed inner and/or outer radii fail to fit the statistics, due mainly to the
slow 70um evolution as stirring moves further out in the disk. This conclusion,
that debris disks are narrow belts, is independent of the significance of 24um
trends for young A-stars. We show that the statistics can also be reproduced
with a model in which disks are stirred by secular perturbations from a nearby
eccentric planet. Detailed imaging is therefore the best way to characterise
the stirring mechanism. From a more detailed look at beta Pictoris Moving Group
and TW Hydrae Association A-stars we find that the disk around beta Pictoris is
likely the result of secular stirring by the proposed planet at ~10AU; the
structure of the HR 4796A disk also points to sculpting by a planet. The two
other stars with disks, HR 7012 and eta Tel, possess transient hot dust, though
the outer eta Tel disk is consistent with a self-stirred origin. Planet
formation provides a natural explanation for the belt-like nature of debris
disks, with inner regions cleared by planets that may also stir the disk, and
the outer edges set by where planetesimals can form. [abridged]
