Within-patch variability refers to those
properties of a physical location in space that it does not share with
other localities (Chesson 1978, 1981, 1985, 1991). The properties
we think of are the organisms present, their properties, and the
physical environment that they experience. We speak of a location in
space as a "patch." Sometimes, the environment will have a natural
discrete structure, with numerous areas of habitat separated from
another, and we naturally call these "habitat patches" for the
organisms of our focus, and are therefore the "patches" referred to
here. More generally, patches can be arbitrary subdivisions of
space. Properties of a patch invariably change over time.
But different patches experience different changes. This is
within-patch variability. Its causes are many and varied.
Some of it is due to within-individual variability from the organisms
on a patch. Provided the number of organisms on a patch is small,
variation due to within-individual variability will be significant at
the level of the patch. Also, the phenotypic composition of the
individuals on a patch will change over time, and this may happen in
different ways on different patches due again to within-individual
variability, causing chance fluctuations in phenotypic
composition. Such effects are contributions to temporal variation
on a patch that are interactions between within-individual variability
and between-individual variation. These sources of variation then can
interact with local population dynamics and dispersal. If local
population dynamics are unstable, such interactions will enhance the
uniqueness of population fluctuations and compositional changes on
individual patches, and so will enhance within-patch variability.
Turning to the physical environment, there are numerous physical
processes that have large elements of chance and so lead to different
trajectories of change in the physical environment on different
patches. This is pure spatio-temporal environmental variation and
contributes directly to within-patch variability. Note that
spatio-temporal environmental variation inevitably interacts also with
population dynamics, and so affects local population changes, enhancing
within-patch variability. Note that different patches will
experience common elements of temporal fluctuations too. The idea
is that these common elements should be partitioned out from the total
variation in the environment over time to leave that which is unique to
the individual patch, within-patch variability. Note that
within-patch variation must lead to differences between patches in
their population densities, phenotypic composition, and physical
environment. But these differences will change over time
contributing to an ever changing spatial pattern. Note also that
patches will differ from one another at any one time due to permanent
differences in their physical properties ("between-patch
variation"). Such differences could be partitioned out from the
total variation from patch to patch to obtain a residual amount due to
within-patch variation. Note, however, that between-patch
variation may combine nonadditively ("interactively") with
between-patch variation and thereby contribute to an ever changing
spatial pattern in that way. That interactive component of
variation would be left over after between-patch and common temporal
variation were partitioned out in an analysis of variance. This
interactive component might therefore might be thought of as part of
within-patch variation if only because of the difficulty of
distinguishing it from other sorts of within-patch variation. Because
this interactively generated variation is likely to have similar
effects on population and community dynamics to within-patch varation
from other sources, there seems to be no good reason to classify it
Within-patch variation is of great interest in scale transition theory (Chesson 1978, 1981, 1991; Chesson et al 2005). It generates variation in space that interacts with nonlinearities in population dynamics, with profound effects on population dynamics on scales of many patches.
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Chesson, P.L. 1985. Coexistence of competitors in spatially and temporally varying environments: a look at the combined effects of different sorts of variability. Theor. Pop. Biol. 28, 263-287.
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