TFor species living in patchy habitats, heterogeneity
in site quality determines their population dynamics
through density-dependent regulation; the basic
premise is that when the local population increases,
some individuals have to use lower quality patches,
resulting in the per-capita population growth being
reduced (Rodenhouse et al. 1997). Ecologists have
traditionally studied differences in patch quality
and their repercussions on population dynamics
using two theoretical models: the ideal free distribution
(IFD) and the ideal despotic distribution
(IDD; Fretwell & Lucas 1970, Sutherland 1996,
Newton 1998). The IFD model assumes that
competition increases as more individuals settle in
a given patch. Consequently, some of these individuals
move to less profitable habitats or patches
where lower levels of competition would compensate
for the lower site quality. The process of
density dependence thereby results in equal fitness
of individuals across all patches. In the IDD model,
the equilibrium density among high-and low-quality
habitats depends on the competitive abilities of
individuals. Strong competitors displace less competitive
individuals to lower quality habitats,
resulting in breeding success differing between
patches. With independence of the mechanisms of
population regulation operating, the natural variability
in food abundance, presence of competitors,
incidence of disturbance, etc., can make a highquality
patch become low-quality or vice versa.
The characteristics and therefore the quality of a