Conservation biology: predicting birds' responses to forest fragmentation.
ABSTRACT Understanding species' ecological responses to habitat fragmentation is critical for biodiversity conservation, especially in tropical forests. A detailed recent study has shown that changes in the abundances of bird species following fragmentation may be dramatic and unpredictable.
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ABSTRACT: Aim Few studies have attempted to assess the overall impact of fragmentation at the landscape scale. We quantify the impacts of fragmentation on plant diversity by assessing patterns of community composition in relation to a range of fragmentation measures.Location The investigation was undertaken in two regions of New Zealand – a relatively unfragmented area of lowland rain forest in south Westland and a highly fragmented montane forest on the eastern slopes of the Southern Alps.Methods We calculated an index of community similarity (Bray–Curtis) between forest plots we regarded as potentially affected by fragmentation and control forest plots located deep inside continuous forest areas. Using a multiple nonlinear regression technique that incorporates spatial autocorrelation effects, we analysed plant community composition in relation to measures of fragmentation at the patch and landscape levels. From the resulting regression equation, we predicted community composition for every forest pixel on land-cover maps of the study areas and used these maps to calculate a landscape-level estimate of compositional change, which we term ‘BioFrag’. BioFrag has a value of one if fragmentation has no detectable effect on communities within a landscape, and tends towards zero if fragmentation has a strong effect.Results We detected a weak, but significant, impact of fragmentation metrics operating at both the patch and landscape levels. Observed values of BioFrag ranged from 0.68 to 0.90, suggesting that patterns of fragmentation have medium to weak impacts on forest plant communities in New Zealand. BioFrag values varied in meaningful ways among landscapes and between the ground-cover and tree and shrub communities.Main conclusions BioFrag advances methods that describe spatial patterns of forest cover by incorporating the exact spatial patterns of observed species responses to fragmentation operating at multiple spatial scales. BioFrag can be applied to any landscape and ecological community across the globe and represents a significant step towards developing a biologically relevant, landscape-scale index of habitat fragmentation.Global Ecology and Biogeography. 04/2010; 19(5):741 - 754.
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ABSTRACT: We evaluated the response of male Reeves's pheasants Syrmaticus reevesii to different forest edges in a fragmented forest landscape in central China using radio-telemetry. Our fieldwork was carried out from April 2000 to August 2003 in the Dongzhai National Nature Reserve within the Dabie Mountains, China. We identified four major types of forest edges: shrub, farmland, road and residential edge. The association of male Reeves's pheasants with these edges was non-random and varied by season, suggesting that land-cover and land-use patterns surrounding forest fragments could have variable effects on habitat use of Reeves's pheasants. Shrub edges were preferred by males in all seasons and male Reeves's pheasant seldom moved > 200 m from this type of edge. Pheasants tended to avoid farmland edges in summer, stayed within 100 m of the nearest road edges in spring and moved farther from residential edges with season shifts. Furthermore, edge use by male Reeves's pheasants also differed between winter and the other three seasons. Our data demonstrated the relationships between edge effects and the spatial distribution patterns of Reeves's pheasants, and suggested that landscape configuration, including juxtaposition of forest and shrubby vegetation, should be incorporated into management and conservation for addressing edge effects at landscape scales. We suggest monitoring the spatial responses of this species to different forest edges over a longer term and at a larger landscape scale.Wildlife Biology 05/2011; · 1.10 Impact Factor
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ABSTRACT: Seed dispersing animals, ranging from small insects to large mammals, provide a crucial service for a large number of plant species worldwide. However, a decline in dispersers due to direct and indirect threats leads to disruptions of seed dispersal processes. As disperser species are differently susceptible to these threats, consequences for ecosystems are hard to predict. Impacts range from hampered regeneration of plant species to shifts in communities and a decline in ecosystem function. Here, we review these threats as well as expected consequences for communities and for the entire ecosystem. We further introduce options to protect dispersers and consider future research directions.Basic and Applied Ecology 01/2012; 13:109-115. · 2.70 Impact Factor
Conservation Biology: Predicting Birds’ Responses
to Forest Fragmentation
critical for biodiversity conservation, especially in tropical forests. A
detailed recent study has shown that changes in the abundances of bird
species following fragmentation may be dramatic and unpredictable.
Cagan H. Sekercioglu1
and Navjot S. Sodhi2
Because of unprecedented rates
of deforestation and forest
degradation, habitat fragmentation
has become a major issue in
conservation biology. Forest
fragments are often scattered
among human-dominated urban
and agricultural areas. Forest
fragmentation results in three
prominent changes: reduced forest
area, increased isolation among
fragments, and creation of edges
where forests abut non-forested
habitats. Because of factors such
influx of invasive competitors and
predators, fragments significantly
decline, over time, in their
conservation value for many forest
species [1,2] (Figure 1). Which
species flourish or perish as
question. Ecological traits such as
body size, diet, mobility and
specialization often correlate
strongly with fragmentation
sensitivity [3–5]. In some
ecosystems, however, it may be
impossible to predict species’
responses to fragmentation .
This is illustrated by a recent study
 which has shown that, in
southeast Australia, bird species’
abundances changed very
unpredictably after the
fragmentation of Eucalyptus
woodlands and even some species
in the same genus differed greatly
in their responses.
Area has been reported as the
strongest predictor of species
richness in forest fragments [8–10].
However, isolation can also affect
species richness and abundance in
fragments . The species–area
relationship (Figure 2) has been
biotic losses from human-modified
landscapes [12,13]. The
rule-of-thumb is that a 90% loss of
habitat area leads to a w25–50%
loss of species . The predictive
power of this relationship may be
weak, because it does not account
for either habitat heterogeneity or
fragmentation, but it is the only
such existing model . Although
the identities of disappearing
species are as important as their
number, how the abundances of
species change because of habitat
degradation has been conceptually
and empirically little developed.
This is a critical lacuna as the
disappearance of functionally
such as specialists, scavengers or
seed dispersers can affect the
entire community .
Fragmentation frequently results
in the ‘cutting’ of the long tail of the
rank-abundance curve, as rare
species, particularly diverse in
tropical forests, often disappear
first (see Figure 1 in ). Such
‘nested’ distributions where
‘‘species present at species-poor
sites are subsets of those present
at species-rich sites’’  mean
that species that will disappear
from fragments can be predicted.
Species that are rare, sedentary
or specialized in their habitat
requirements are expected to have
lower persistence .
Mac Nally  examined whether
the relative abundances of
woodland bird species can be
predicted following fragmentation.
He surveyed birds in 73 remnants
ranging from 15 ha to 2900 ha in
size in south-eastern Australia.
Because of the absence of pre-
fragmentation data, three large
remnants (16,000–41,000 ha) were
used as reference sites. Although
changed little, suggesting
reorganization of abundances at
ecological time frames, the
changes in the abundances of
individual species were not
predictable. Fragmentation did not
necessarily favor species common
at reference sites. The bird
communities in smaller fragments
werealso not nestedsubsets of the
reference ones, contrary to what
some studies have shown
elsewhere [4,9,17–19]. Mac Nally
 suggests that our knowledge of
how bird communities organize
themselves in fragmented
landscapes is shallow and that
more research should be
Figure 1. An example of
Southeast Asian forest spe-
Barbet (Megalaima oorti).
Photo by Malcolm Soh.
Current Biology Vol 17 No 19
conducted in this direction. We
agree with Mac Nally that we must
look beyond predicting species
richness in human-altered habitats
and focus on the factors that
change species abundances,
which he originally depicted with
the ‘abundance spectrum’.
We suggest that nestedness
analysis be more widely (albeit
judiciously ) employed in
fragmentation studies, and that
existing fragmentation data be
meta-analyzed to understand
regional and ecological differences
in nestedness. Bird communities
are often comprised of distinctive
groups of species with similar
responses to fragmentation . In
nestedness analyses, pooling all
species can obscure important
patterns  as a result of the
idiosyncratic responses of more
mobile and less specialized
species . Specialized and
sedentary species, typical of
tropical humid forests, are more
likely to show nested distributions
, and these species are also the
ones that are more extinction-
prone [9,10,20]. Other examples of
more nested groups are forest
understory species, large-bodied
species and species of
conservation concern [4,9].
Comparing the nestedness of
ecologically distinct groups will
reveal those that are more nested
and hence more vulnerable
to fragmentation [4,9].
of the nestedness matrix (a graphic
representation of species’
distributions, see Figure 1 in ) is
also valuable, as some species,
including sensitive ones, may be
affected by factors other than
fragmentation . Used in this
manner, nestedness analysis
becomes an important
Highly nested distributions imply
that a few large patches can
conserve most or all species.
However, statistically significant
nestedness does not mean perfect
nestedness , and many species
can exhibit idiosyncratic patch
occupancies . Differences in
species extinction or colonization
rates are the two main causes of
nestedness in fragments. Species
richness patterns become less
nested and more unpredictable if
species vary little in their
vulnerability to extinction or in their
ability to colonize fragments [4,18].
Birds that are less specialized
and/or have small home ranges
are less vulnerable to extinction.
Colonization likelihood is higher
if birds are more mobile (e.g.
long-distance migrants, nomadic
species)  or if fragments are
Because mobile and generalist
bird species reduce nestedness,
temperate, more seasonal, and
more open ecosystems, which
harbor higher proportions of
migrant species and habitat
generalists (Figure 3), should be
less nested than tropical humid
forests [4,9,19]. But global
comparisons are lacking.
Mac Nally’s  study took place
in a temperate, dry habitat
(300–700 mm of rain per year) and
open Eucalyptus woodlands. As
expected, the bird community is
relatively mobile and generalized,
helping explain the reduced
nestedness and high idiosyncrasy
observed. The study species, on
average, resemble other
temperate woodland birds in
their mobility and habitat
specialization, and are more
mobile and more flexible in their
habitat use than most tropical
forest birds (Figure 3).
Increased habitat similarity
between fragments and the
surrounding matrix also reduces
isolation and nestedness. A more
‘permeable’ matrix can increase
the presence of some common,
generalist species in small
fragments, but reduced isolation
can also hamper the persistence of
some rare, specialized species in
larger fragments if these birds
leave and do not come back .
contributes to the idiosyncrasy of
species distributions in the Mac
Nally study . Compared to
closed, humid tropical forests,
open, dry, temperate woodlands
are more similar to surrounding
farmlands. Interestingly, the study
fragments do not exhibit a
species–area relationship —
S = 75.6*A20.0027, r2= 0.0033,
based on species lists provided
by Mac Nally  — further
suggesting that the fragments
in this landscape are less
isolated than the surrounding
matrix than is typical of
tropical forest remnants.
The presence of an unusual
‘despotic’ species, the colonial and
aggressive Noisy Miner (Manorina
melanocephala), is another factor
that contributes to the difficulty of
abundances in this system. This
species dominates forest
fragments and drives out most
native forest species, regardless of
their ecological differences .
Such a native species is hardly
equaled in other forest
fragmentation studies, especially
in the tropics. As open, dry
woodland habitats that are
frequented by relatively
generalized and mobile bird
species and where fragments
are dominated by the unique
Noisy Miners, Australian
log10 Forest patch area (ha)
S2 (adj. R2 = 97.1%)
S3 (adj. R2 = 83.4%)
S4 (adj. R2 = 0.0%)
S1 (adj. R2 = 92.2%)
Number of bird speciesNumber of bird species
log10 Forest patch area (ha)
Figure 2. Species–area relationships for four avian functional groups that vary in their
Reproduced with permission from .
ironbark woodlands are not
representative of most forests,
underlining the need for global
syntheses of avian responses to
The difference between
a species’ abundance rank in the
reference plots and its rank in
fragments is a key measure of its
response to fragmentation.
Ecological correlates of rank
differences can illuminate the
causes of fragmentation
sensitivity. Based on the
fragments’ species lists we
obtained from Mac Nally , we
compared the basic ecological
characteristics of species that
declined versus increased in the
smallest (A2) study fragments in
relation to the reference areas.
Forest specialists, insectivores,
nectarivores, and species with
lower clutch sizes were
open habitat species,
granivores, and raptors
increased in small fragments.
Interestingly, so did the large-
bodied species (median body
mass 142 g versus 21 g),
contrary to most tropical forest
Even when species responses
to fragmentation are highly
idiosyncratic, analyses of rank
differences can reveal interesting
ecological patterns and
highlight potentially vulnerable
species. There is a major need for
global meta-analyses of
measures [17,18] with existing
data. These analyses will help
formulate the drivers of
fragmentation sensitivity and
nestedness, explain regional
differences, and contribute to
the development of ecological
theory . For example, the
same characteristics that
make fragments less nested
(more permeable matrix, high
proportion of generalist, mobile,
species) can also make them
more vulnerable to invasive
species, but this has been little-
studied. We hope that Mac
Nally  will inspire similar
studies worldwide, particularly
in the tropics where an improved
understanding of species’
responses to fragmentation is
critical to the conservation of
1. Sodhi, N.S., Lee, T.M., Koh, L.P., and
Dunn, R.R. (2005). A century of
avifaunal turnover in a small tropical
rainforest fragment. Anim. Conserv. 8,
2. Sodhi, N.S., Lee, T.M., Koh, L.P., and
Prawiradilaga, D.M. (2006). Long-term
avifaunal impoverishment in an isolated
tropical woodlot. Conserv. Biol. 20,
3. Sekercioglu, C.H., Ehrlich, P.R.,
Daily, G.C., Aygen, D., Goehring, D., and
Sandi, R. (2002). Disappearance of
insectivorous birds from tropical forest
fragments. Proc. Natl. Acad. Sci. USA 99,
4. Martinez-Morales, M.A. (2005). Nested
species assemblages as a tool to detect
sensitivity to forest fragmentation: the
case of cloud forest birds. Oikos 108,
5. Posa, M.R.C., and Sodhi, N.S. (2006).
Effects of anthropogenic land use on
forest birds and butterflies in Subic
Bay, Philippines. Biol. Conserv. 129,
6. Mac Nally, R., Bennett, A.F., and
Horrocks, G. (2000). Forecasting the
impacts of habitat fragmentation.
Evaluation of species-specific predictions
of the impact of habitat fragmentation
on birds in the box-ironbark forests of
central Victoria, Australia. Biol. Conserv.
7. Mac Nally, R. (2007). Use of abundance
spectrum and relative abundance
distributions to analyze assemblage
change in massively altered landscapes.
Am. Nat. 170. DOI: 10.1086/519859. In
8. Castelletta, M., Thiollay, J.M., and
Sodhi, N.S. (2005). The effects of extreme
forest fragmentation on the bird
community of Singapore Island. Biol.
Conserv. 121, 135–155.
9. Lees, A.C., and Peres, C.A. (2006). Rapid
avifaunal collapse along the Amazonian
deforestation frontier. Biol. Conserv. 133,
10. Sekercioglu, C.H. (2007). Conservation
ecology: area trumps mobility in fragment
bird extinctions. Curr. Biol. 17,
11. Stouffer, P.C., and Bierregaard, R.O.
(1995). Use of Amazonian forest
fragments by understory insectivorous
birds. Ecology 76, 2429–2445.
12. Brook, B.W., Sodhi, N.S., and Ng, P.K.L.
(2003). Catastrophic extinctions follow
deforestation in Singapore. Nature 424,
13. Pandit, M.K., Sodhi, N.S., Koh, L.P.,
Bhaskar, A., and Brook, B.W. (2007).
Unreported yet massive deforestation
driving loss of endemic biodiversity in
Indian Himalaya. Biodivers. Conserv. 16,
14. Simberloff, D. (1992). Do species-area
curves predict extinction in fragmented
forest? In Tropical Deforestation and
Species Extinction, T.C. Whitmore and
J.A. Sayer, eds. (London: Chapman &
Hall), pp. 75–89.
15. Sodhi, N.S., Liow, L.H., and Bazzaz, F.A.
(2004). Avian extinctions from tropical and
subtropical forests. Annu. Rev. Ecol. Evol.
Systemat. 35, 323–345.
16. Sekercioglu, C.H. (2006). Increasing
awareness of avian ecological function.
Trends Ecol. Evol. 21, 464–471.
17. Fischer, J., and Lindenmayer, D.B. (2005).
Perfectly nested or significantly
nested - an important difference for
conservation management. Oikos 109,
18. Atmar, W., and Patterson, B.D. (1993).
The measure of order and disorder in
the distribution of species in
fragmented habitat. Oecologia 96,
19. Wethered, R., and Lawes, M.J. (2005).
Nestedness of bird assemblages in
fragmented Afromontane forest: the effect
of plantation forestry in the matrix. Biol.
Conserv. 123, 125–137.
20. Sekercioglu, C.H., Daily, G.C., and
Ehrlich, P.R. (2004). Ecosystem
consequences of bird declines. Proc. Natl.
Acad. Sci. USA 101, 18042–18047.
1Center for Conservation Biology,
Department of Biological Sciences,
Stanford University, 371 Serra Mall,
Stanford, CA 94305, USA.2Department
of Biological Sciences, National
University of Singapore, 14 Science
Drive 4, Singapore 117543, Republic of
Percent of bird species
Mac Nally (2007)
Mac Nally (2007)
(5086 species) and temper-
ate woodland birds (472
species), with the 123 study
Sedentary species do not
movements (for example,
migration, altitudinal migra-
tion, nomadic movements).
confined to only one main
habitat (for example, forest
The list of study species
was provided by MacNally.
For a description of the
bird ecology database that
was used for this analysis,
Current Biology Vol 17 No 19