relevant to management plans. Simplified repre-
sentations of woodland dynamics view a stand of
trees as going through phases of youth, building,
maturity, and senescence, each of which may sup-
port differing suites of interacting species. Reserves
should therefore be large enough (or managed) to
ensure that they contain enough habitat patches at
different stages of patch life-cycles to support a full
array of niches. A related and often contentious
issue is how fire regimes are managed. In fire-prone
regions there is often a cyclical pattern of post-burn
succession and fuel accumulation, leading to an
increased likelihood of fire, repeating the cycle. The
maintenance of a particular fire regime and patch
mosaic structure may be of crucial relevance to
species diversity in a reserve system, but is often
poorly understood (Short and Turner 1994; Milberg
and Lamont 1995). Fire is also politically contentious
because of the threat it poses to people and property.
Much active management of nature reserves is
thus about keeping a mosaic of different succes-
sional stages, and not allowing the whole of the
reserve to march through the same successional
stage simultaneously. The relevance of such succes-
sional dynamics to species changes in reserve sys-
tems appears to have received much less attention
in the theoretical conservation science literature
than its significance warrants (but see Pickett et al.
1992). Moreover, continuing changes in the habitats
of the matrix can also be extremely important to the
fate of species populations in the reserves them-
selves (Stouffer and Bierregaard 1995, 1996; Gascon
et al. 1999; Daily et al. 2003).
10.9 The implications of nestedness
As we established in Chapter 5, many island and
habitat island data sets exhibit nestedness. That is,
when organized into a series of increasing species
richness, there is a significant tendency for the
species present in species-poor (small) patches to be
found also in successively richer (larger) patches.
Although nestedness can be driven by selective col-
onization or by habitat nestedness, it appears that
differential extinction plays a major role in produc-
ing nested structure in many habitat island data
sets (Wright et al. 1998). A nestedness analysis can
contribute a simple answer to the SLOSS question,
as a strong degree of nestedness implies that most
species could be represented by conserving the
richest (largest) patch. A low degree of nestedness,
on the other hand, would mean that particular
habitat patches sample distinct species sets and that
an array of reserves of differing size and internal
richness may be required to maximize regional
diversity (cf. Kellman 1996). Knowledge of nested
subset structure might therefore provide a basis for
predicting the ultimate community composition of
a fragmented landscape, particularly if it is possible
to attribute patterns to particular causes (Worthen
1996, Fischer and Lindenmayer 2005).
Blake’s (1991) study of bird communities in iso-
lated woodlots in east-central Illinois shows how
nestedness calculations can provide useful insights.
He demonstrated a significant degree of nested-
ness, particularly among birds requiring forest inte-
rior habitat for breeding and among species
wintering in the tropics. In contrast, species breed-
ing in forest-edge habitat showed more variable
distribution patterns. Blake’s findings resonate
with those reported from São Paulo by Patterson
(1990), who found significant nestedness amongst
sedentary bird species, but that the full data set (i.e.
also including transient species) was non-nested.
These results indicate that some species, often those
of most conservation concern, will be lacking from
any number of small patches, but can be found in
the larger, richer patches.
Tellería and Santos (1995) have demonstrated
the apparent importance of nestedness of habitat.
They studied the winter use of 31 forest patches
(0.1–350 ha) in central Spain by the guild of pari-
forms (ParusandAegithalos, Regulus, Sitta, and
Certhia—tits, goldcrests, nuthatches, and treecreep-
ers). They found that birds with similar habitat
preferences tend to disappear simultaneously with
reduction in forest size, thereby producing a nested
pattern of species distribution.
Simberloff and Martin (1991) have argued that
establishing nestedness across a whole system is no
longer particularly exciting, but that some benefit
can come from examining discrepancies from nest-
edness. Cutler (1991) developed an index, U, which
was designed to account for both unexpectedTHE IMPLICATIONS OF NESTEDNESS 275