Island vs. countryside biogeography: an examination of how Amazonian birds respond to forest ...

14 Pages·2015·1.76 MB·English

Island vs. countryside biogeography: an examination of how
Amazonian birds respond to forest clearing and fragmentation
JARED D. WOLFE,1,2,3,4,(cid:2) PHILIP C. STOUFFER,1,4 KARL MOKROSS,1,4 LUKE L. POWELL,1,4
AND MARINA M. ANCIA˜ES5
1SchoolofRenewableNaturalResources,LouisianaStateUniversityAgriculturalCenter,BatonRouge,Louisiana70803-6202USA
2USDAForestService,PacificSouthwestResearchStation,RedwoodSciencesLaboratory,Arcata,California95521USA
3KlamathBirdObservatory,Ashland,Oregon97520USA
4BiologicalDynamicsofForestFragmentsProject,InstitutoNacionaldePesquisasdaAmazoˆnia,Manaus69011Amazonas,Brazil
5Coordenac¸a˜odePesquisaemEcologia,InstitutoNacionaldePesquisasdaAmazoˆnia,Manaus69011Amazonas,Brazil
Citation: Wolfe, J. D., P. C. Stouffer, K. Mokross, L. L. Powell, and M. M. Ancia˜es. 2015. Island vs. countryside
biogeography: an examination of how Amazonian birds respond to forest clearing and fragmentation. Ecosphere
6(12):295.http://dx.doi.org/10.1890/ES15-00322.1
Abstract. Avian diversity in fragmented Amazonian landscapes depends on a balance between
extinction and colonization in cleared and disturbed areas. Regenerating forest facilitates bird dispersal
withindegradedAmazonianlandscapesandmaytipthebalanceinfavorofpersistenceinhabitatpatches.
Determining the response of Amazonian birds to fragmentation may be hindered because many species
use adjacent second growth matrices thereby limiting the applicability of island biogeography to predict
species loss; alternatively, a countryside biogeographic framework to evaluate the value of regenerating
forestmaybemoreappropriate.Here,weusedpoint-countandcapturedatatocompareAmazonianbird
communities amongcontinuous forest, 100haforestfragments withadjacentsecond growth,youngand
oldersecondgrowthplots,and100haforestedislandsboundedbywater,totesttheapplicabilityofisland
biogeographyonthemainlandandtoassesstheecologicalvalueofaregeneratingmatrix.Amongforaging
guilds, understory insectivores and flocking species were nearly absent on true islands. Fragments
surroundedbyyoungsecondgrowthwerespeciesrich,suggestingthatadevelopingmatrixmaymitigate
extinction associated with fragmentation. Our findings reinforce that true islands are often extinction-
driven systems with distinct, depauperate communities. In contrast, succession of bird communities in
second growth facilitates recolonization of forest fragments, permitting fragments as small as 100 ha to
support birdcommunities similarto continuous forest.
Key words: Balbina; central Amazon; continuous forest; countryside biogeography; forest fragment; island
biogeography;secondgrowthmatrix;speciesrichness;tropicalbird.
Received27May2015;revised12August2015;accepted17August2105;published22December2015.Corresponding
Editor:D.P.C.Peters.
Copyright: (cid:2) 2015 Wolfe et al. This is an open-access article distributed under the terms of the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the
originalauthorandsourcearecredited.http://creativecommons.org/licenses/by/3.0/
(cid:2)E-mail:[email protected]
INTRODUCTION applying the theory of island biogeography
(‘island model’ hereafter) on the mainland stem
The utility of island biogeography to predict from variation in the hostility of the matrix,
species loss within mainland habitat patches has where the surrounding landscape interspersed
frequently been questioned (Mendenhall et al. between habitat patches are often more salubri-
2012, 2014, Fahrig 2013). Criticism towards ous than water surrounding true islands (Men-
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WOLFE ETAL.
denhall et al. 2014). Differences in matrix influence on hummingbird abundance and the
hostility, such as water (hostile) versus regener- subsequent seed set of native plants species they
ating forest, determines how animals use and pollinate (Hadley et al. 2014). These results
dispersethroughthelandscape,therebyresulting suggest that habitat patches in Costa Rica may
in divergent biogeographic processes and differ- actmoreliketrueislandswheresomehumming-
entratesofspecieslossinhabitatpatches.Infact, birds may respond to the regenerating matrix as
the matrix surrounding remnant habitat patches extremely hostile and are, therefore, subject to
may even provide some ecological value to area effects as predicted by the island model.
wildlife which led Daily (1997) to suggest a Although the response of birds to fragmentation
new theoretical framework, called ‘countryside appear contradictory in the aforementioned
biogeography’, to study the diversity, abun- studies from the Amazon and Costa Rica, the
dance, conservation and restoration of species ecological value of landscape matricesfrom both
in human-dominated landscapes. More specifi- study sites was measured within fragments,
cally, countryside biogeography recognizes that rather than within the matrix itself. Clearly,
many human-dominated landscapes are not measuring birds within the matrix to quantify
analogous to inhospitable bodies of open water the ecological value of a regenerating tropical
interspersed between islands of habitat—a nec- forest represents a critical step towards predict-
essary assumption of the island model. ing species loss in the Neotropical countryside
Countryside biogeography is particularly rele- (Gardner et al. 2007).
vanttotropicalforest-dwellingbirdsthatmaybe Todate,researchthathassampledbirdswithin
dispersal limited and reliant upon human-dom- the matrix to assess its ecological value mostly
inated matrices to maintain metapopulation relied on examining species richness between
connectivityinheterogeneouslandscapes(Seker- regenerating and pristine forest; these studies
cioglu et al. 2002). For example, Stouffer et al. have produced largely contradictoryand region-
(2011)demonstratedthatAmazonianforestbirds dependent results. For example, Barlow et al.
wereabletodispersefromsourcepopulationsin (2007)foundfewerspeciesinregeneratingmatrix
pristine habitat through a regenerating pastoral relative to primary forest in Brazil, while Blake
matrix to recolonize previously depauperate and Loiselle (2001) documented more species
forest fragments, suggesting that species are lost withinyoungmatrixrelativetoprimaryforestin
followingisolation,butthetrajectoryoflossdoes CostaRica.Theinfluenceofregiononpatternsof
not continue downward when coupled with species richness within the matrix was exempli-
matrix recovery (Marsden et al. 2003, Ferraz et fied by Martin and Blackburn (2014) where
al. 2007, Laurance 2008, Stoufferet al.2011). Not endemic species in Honduras were found to be
only does an adjacent matrix facilitate fragment less common in the matrix relative to primary
recolonization,butitmayalsodampenpredicted forest,whencomparedwithbirdcommunitiesin
area effects associated with the island model similar aged forests in Sulawesi. Dissimilar
(Zimmerman and Bierregaard 1986) as demon- responses of matrix bird communities probably
strated in the central Amazon where fragments reflect four differences among the aforemen-
of different sizes yielded similar estimates of tioned studies: (1) differences in avifauna and
species richness as the adjacent matrix matured their respective ability to exploit resources; (2)
(Stouffer et al. 2006). Additionally, many species differences in successional pathways; (3) differ-
recolonize Amazonian forest fragments, even if ences in distance to source populations; and (4)
they do not persist (Stouffer et al. 2011) demon- differencesinmatrixage.Regionaldissimilarities
strating that presence or absence of a matrix will are potentially further complicated by the asym-
result in the disproportionate influence of either metric response of foraging guilds to the age of
extinction or colonization on Amazonian bird regenerating matrix. In general, frugivorous and
assemblages in forest fragments and islands nectivorous birds, which are relatively more
bounded by water, respectively (Terborgh et al. common in Neotropical forests, often fare better
2001). whensubjectedtoclearingandsubsequentforest
Conversely, forest patch size within a regener- regeneration (although see Hadley et al. 2014)
ating matrix in Costa Rica yielded a strong relative to their insectivorous counterparts (Karr
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et al. 1990, Sekercioglu et al. 2002). tion.Totestthiscentralhypothesis,wemeasured
Stouffer et al. (2006) and Powell et al. (2013) fourpredictions:(1)birdscandispersethrougha
demonstrated that the presence of insectivorous regenerating matrix to recolonize forest frag-
birds on the periphery of Amazonian forest mentsbutwillbelessabletodisperseoverwater,
fragments was positively correlated with age of thus, true islands will be less species rich when
the surrounding matrix, with fewer birds cap- compared to similarly-sized forest fragments
tured in fragments bordered by young forest. In embedded within a regenerating matrix; (2)
particular, forest-obligate guilds such as terres- becausebirdsaremorepronetodispersethrough
trial insectivores, ant-followers, flock obligates mature second growth (25 years old) relative to
and arboreal insectivores were found to be most young second growth (15 years old), young
sensitive to surrounding matrix age, possibly second growth will be significantly less species
reflectinganinabilityofcertainforagingguildsto rich than mature second growth; (3) forest-
disperse through young second growth to obligatebirds(terrestrialinsectivores,ant-follow-
recolonize isolated forest fragments (Stouffer et ers, flock obligates and arboreal insectivores) are
al. 2006). Antithetically, hummingbirds, gap dispersallimited,thereforetrueislandswillhave
specialists and some frugivores exhibited in- differentcommunitystructuredrivenbythelack
creased abundances within fragments surround- of forest-obligate birds compared to similarly-
ed by a young matrix (Stouffer et al. 2006). sized forest fragments; and (4) forest-obligate
Clearly, the age of regenerating Amazonian birds (terrestrial insectivores, ant-followers, flock
forest wields influence over how bird species obligates and arboreal insectivores) are more
perceive and use the matrix. pronetodispersethroughmaturesecondgrowth
A better understanding of how a range of (25 years old) relative to young second growth
matrix conditions (i.e., water, young and mature (15 years old), therefore young second growth
second growth) affect bird communities within will have a significantly different community
isolates as well as within the matrix would have structure driven by the lack of forest-obligate
significant theoretical and conservation implica- birds compared to mature second growth.
tions. The complex nature of historic and
continued degradation within the Amazon basin METHODS
providesauniqueopportunitytoconductsucha
study. Habitat loss in the Amazon basin is The study was conducted in terra firme forest
dynamic due to ecological and economic forces, at the Biological Dynamics of Forest Fragments
as reflected by hydroelectric development, large- Project (BDFFP), about 80 km north of Manaus,
scale pasture abandonment and subsequent Brazil and on two islands, each about 100 ha in
forest regeneration (Neeff et al. 2006). In this size (Sapopara and Relo´gio), in the Balbina
study we worked within the heterogeneous reservoir, approximately 150 km north of Man-
central Amazonian landscape, using multiple aus. Balbina dam construction was completed in
methods to describe bird communities on true 1989; Sapopara and Relo´gio have been isolated
islands boundedby water, in fragments within a since then. Forest fragments at BDFFP, including
matrix, in second growth of two ages, and in two 100-ha fragments, were isolated from 1980
continuous forest. In general, our study focused through 1990. We also worked in 15- and 25-
on determining the applicability of island or year-old second growth and continuous primary
countryside biogeographic frameworks to study forest at the BDFFP (Fig. 1). For more informa-
birds in degraded and heterogeneous forests in tionaboutthestudysiteseeStoufferetal.(2006).
the Amazon. Totestthefouraforementionedpredictionswe
More specifically, our study aimed to test the employed both understory mist-netting and
following hypothesis: if birds can disperse point countstoaccount forbirdsineachstratum
through young and mature second growth, of forest. Point counts can detect species that are
presumably at different rates, but rarely over vocal, conspicuous, or occupy the canopy and
water, then forest fragments within a regenerat- mid-story. Conversely, mist-netting is useful for
ing matrix will be subject to more colonization detecting quiet or skulking understory species
and islands bounded by water to more extinc- (Ralphetal.1995).Mistnettingandpointcounts
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Fig.1.MapofstudyregionsattheBalbinareservoirandBiologicalDynamicsofForestFragmentsProject80
km and 150kmnorthof Manaus, Brazil, respectively.
were conducted in five treatments: 100-ha forest roundedbyatleast300mofopenwaterwithina
fragment (surrounded by a 50-m buffer of 15- landscape of larger islands and continuous
year-oldsecondgrowthfollowedbyasecondary forest), older second growth forest (25 years old
50-m buffer of 25-year-old second growth adja- adjacent to continuous forest), young second
cent to continuous forest), 100-ha island (sur- growth forest (15 years old adjacent to continu-
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ous forest) and continuous forest. Treatments andopenedfrom0600to1400forasingledayof
were aggregated into five regions: Dimona (two sampling. All captured birds were banded with
transects within a 100-ha forest fragment, two uniquely numbered aluminum bands. We mist-
transects within older second growth and two netted between June and November in 2010–
transects within continuous forest), Porto Alegre 2013, where we collected 4 days of capture data
(two transects within a 100-ha forest fragment at100-ha island transects,4 daysof capturedata
and two transects within continuous forest), at young second growth transects, and 6 days of
Colosso (two transects within older second capture at 100-ha forest fragment transects,
growthforest,twotransectswithinyoungsecond continuous forest transects and older second
growth forest and two transects within continu- growth transects.
ous forest), KM41 (two transects within contin- To measure differences in species richness
uousforest),andBalbina(onetransectoneachof between forest fragments, islands, regenerating
two 100-ha islands). Each BDFFP region was up matrix and continuous forest (see predictions 1
to 50 km apart, and Balbina was 70 km to the and 2), point count and capture data were
north of the nearest BDFFP region (Fig. 1). organized by number of individuals per species
Despite a distance of 70 km between Balbina by treatment. For capture data, the number of
and the other regions, each region is character- speciescapturedat each transect was divided by
ized by terre firme forest occurring on ancient associatedeffort(mistnethours)then multiplied
soils within the Guinean Shield, resulting in by 100 to yield a standard number of species
comparable bird communities. Our assumption captured per 100 mist net hours across each
ofsimilarbirdcommunitiesacrossthestudyarea transect irrespective of differences in sampling
is verified by earlier work that documented effort. We used program EstimateS (Colwell
remarkablysimilarbirdcommunitiesthroughout 2005) to produce Chao1 abundance-based esti-
the Guinean shield, from Manaus through mates of species diversity and Chao-Jaccard
French Guiana (Willis and Oniki 1988, Johnson abundance-based similarity indices to compare
et al. 2011). Furthermore, we only captured one treatments. The Chao1 diversity index uses the
resident species (in addition to a single migrant) ratio of ‘singletons’ and ‘doubletons’ (species
at Balbina that we didn’t capture at BDFFP detected only once or twice, respectively) to
further emphasizing the similarity of these generate predicted estimates of species richness.
communities. Significance between Chao1 estimates are based
Each transect was 200 m in length, at least 200 on non-overlapping 95% confidence intervals
m apart from any neighboring transect, and generated through a bootstrapping routine in
hosted three point count locations at 0 m, 100 m EstimateS.TheformulausedforChao1estimates
and 200 m along the transect. Twenty minute are based on Chao (1987) where Sobs refers to
point counts were conducted in 2012 during our total number of species observed in all samples
studyarea’s prolonged dry season, June through pooled and F1 and F2 refer to singletons and
November; each point count occurred between doubletons(species detectedonlyonceortwice),
05:55 and 07:20 am. Given the diversity of bird respectively:
species in the central Amazon, we used 20 F2
minutes (as opposed to five or 10 minutes) to Sˆchao1 ¼SobsþF12:
maximize the number of species encountered at 2
each transect. For each point count, the number To measure overall community similarity
of individuals per species was conservatively between forest fragments, islands, regenerating
estimated using song, call and visual documen- matrix and continuous forest (see predictions 3
tation within a 50 m radius; flyovers were not and 4) we used Chao’s abundance-based Jaccard
includedintheanalysis.Eachpoint-countstation community similarity indices. According to
wasvisitedtwicebyJ.D.Wolfeondifferentdays, Colwell (2005), Chao’s abundance-based Jaccard
yielding1220-minutepointcountspertreatment community similarity indices are based on the
ineacharea.Eachtransectalsohostedalineof16 probability that two randomly chosen individu-
mist-nets(NEBBA-typeATX,36mmmesh,1232 als, one from each of the two samples, both
m),with nets set with the bottom at ground level belong to species shared by both samples (but
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not necessarily to the same shared species; Chao are robust. We accounted for unequal effort
etal.2005,Colwell2005).Thisapproachhasbeen among transects and treatments using the sensi-
shown to substantially reduce the negative bias tivitytestbyrandomlyselectingfourcaptureand
that undermines the usefulness of traditional four point count occasions per treatment (con-
similarity indexes, especially with incomplete tinuous, 100-ha fragment, 100-ha island, young
sampling of rich communities (Chao et al. 2005, and mature second growth) thereby creating
Colwell 2005). The formula used for Chao- complete equal effort among the subset of data,
Jaccard abundance-based similarity indices are then repeated a portion of the above analysis on
based on Chao et al. (2005), and described by the subset of data. More specifically, we gener-
Colwell (2005) where Q is the frequency of ated Chao1 diversity estimates, compared com-
1
uniques,Q the frequency of duplicates munities using the Chao-Jaccard abundance-
2
based similarity index, and finally used package
" #
vaˆrðSˆ Þ¼Q þ 1(cid:2)Q1(cid:3)2þ(cid:2)Q1(cid:3)3þ1(cid:2)Q1(cid:3)4 Vegan in Program R to ordinate and compare
chao2 2 2 Q2 Q2 4 Q2 communities categorized by species for each
treatment.
and
Q2 RESULTS
Sˆ ¼S þ 1:
chao2 obs
Q
2
We recorded 3,339 individual birds represent-
To measure community similarity between ing 180 species during point counts (Appendix:
forest fragments, islands, regenerating matrix Table A1). We banded 3,916 individual birds
and continuous forest with respect to foraging representing 121 species (Appendix:Table A2).
guild (see predictions 3 and 4), we separately Our first prediction, that islands are less species
categorizedmist-nettingandpointcountdataby rich than fragments, was supported by point
foraging guild and species (following Stouffer et count data where we found significantly fewer
al. 2006; Appendix: Tables A1 and A2). We used bird species on true islands compared to frag-
package Vegan in Program R (Dixon 2003, R ments and all other treatments except young
Development CoreTeam 2010) to separately second growth (Fig. 2). Although not significant,
ordinate capture and point count data, catego- capture data also yielded the lowest number of
rized by foraging guild and species within species on true islands relative to fragments and
treatment, via a Detrended Correspondence all other treatments (Fig. 2). Similarly, point
Analysis (DCA). We statistically examined dif- count and capture data supported our second
ferences among bird communities within each predictionthatyoungsecondgrowthwouldhost
treatment, by foraging guild and species, via a fewerspeciesthanmaturesecondgrowth;young
permutationtestusing1000iterationsinpackage secondgrowthwasthemostspeciesdepauperate
Vegan. In addition to estimating diversity, comparedtoallothernon-islandtreatments(Fig.
community similarity and ordinations, we used 2).Ourthirdprediction,thatislandandfragment
package Car (Fox et al. 2012) in program R to bird communities would be significantly differ-
employatwo-wayANOVAusingtypeIIIsumof ent, was supported by both point count and
squares to test guild and treatment effects on capture data. For example, the Chao-Jaccard
species abundance for both point count and abundance-based similarity index at the treat-
capture data. We choose type III sum of squares ment scale suggested that islands and fragments
ANOVA because it relies on unweighted means were the third and second most dissimilar bird
that account for correlations between indepen- community using capture and point count data,
dent variables due to unequal sample sizes. respectively, when ranked against all other
Because our chosen diversity estimator possible treatment comparisons (Fig. 3). Similar-
(Chao1), community similarity metric (Chao- ly, at the region scale, island bird communities
Jaccard abundance-based similarity index) and were the most dissimilar when compared to all
ordinationmethodology(DCA)maybesensitive other regions (Appendix: Fig. A1). Supporting
to variation in effort and sample size, we also the assertion that island communities are the
conducted a sensitivity test to ensure our results most dissimilar, Detrended Correspondence
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Fig. 2. Chao1’s estimated number of species by treatment (10-ha forest fragment, 100-ha island, continuous,
oldersecondgrowthforest,andyoungsecondgrowthforest)andregion.Filledcirclesrepresentpointcountand
open boxes represent capture data.Allvaluesare shown with 95% confidence intervals.
Fig.3.Chao’sabundance-basedJaccardcommunitysimilarityindicesbasedonpointcountdatabytreatment
shown with standard error bars. Filled circles represent point count and open boxes represent capture data.
Comparisons are ranked frommost toleast similar.
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Fig.4.Detrendedcorrespondenceanalysis(DCA)ordinationofcapturedata,classifiedbyforagingguildand
treatment. Asterisks represent significance levels where * and ** represent p , 0.1 and p , 0.05, respectively.
Numbers in parentheses represent number of species within foraging guild and total number of individuals
captured withineach foraging guild.
Analysis (DCA) results suggested that, based on differencesweredrivenbytheabundanceofnon-
mist-net data, true islands represented signifi- forest and hummingbird foraging guilds associ-
cantly different communities (p , 0.05) when ated with young second growth (Appendix:
classified by foraging guild and species (Figs. 4 Table A1).
and 5). Guild ordinations based on point count In general, continuous, forest fragment and
dataalsosuggestedthattrueislandsapproached older second growth bird communities were
significance (p , 0.1). Support for our fourth mostsimilarirrespectiveofmethod(mist-netting
prediction, that young and mature second orpointcount).Estimateddiversityandcommu-
growth bird communities would be significantly nity similarity analyses showed that bird com-
different,wasnotsupportedbytheChao-Jaccard munities on true islands and in young second
abundance-based similarity index at the treat- growth forest were most depauperate and
ment scale based on species captured (Fig. 3). dissimilar from communities in continuous for-
However, when grouped by guild, the DCA est. Interestingly, when classified by species,
ordination based on capture data yielded a forest fragment, older second growth, young
significant difference between young second second growth and true islands all yielded
growth and mature second growth thereby significantly different bird communities (p ,
supporting our fourth prediction (Fig. 4). These 0.05;Figs.6and7).Ourtwo-wayANOVAusing
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Fig.5.Detrendedcorrespondenceanalysis(DCA)ordinationofcapturedata,classifiedbyforagingguildand
treatment. Asterisks represent significance levels where* and** represent p , 0.1and p ,0.05,respectively.
type III Sum of Squares based on foraging guild Additionally,twospeciesparticularlycommonin
classification, for point count (df ¼ 48, f-stat ¼ second growth samples were also found on true
10.04,p,0.001)andmist-netdata(df¼44,f-stat islands: Myiarchus ferox and Notharchus macro-
¼ 6.57, p , 0.001) yielded highly significant rhynchus (although, N. macrorhynchus more asso-
differences among treatments and guilds. Differ- ciated with older forest at BDFFP; Cohn-Haft et
ences were driven by high number of core al. 1997). In general, woodpeckers (Picidae) and
frugivores in older second growth, and the toucans (Ramphastidae) were well represented
absence of flock obligates, flock dropouts and ontrueislandswhileterrestrialinsectivores(e.g.,
terrestrial insectivores on true islands and in Formicariuscolma,CorythopistorquatusandScleru-
young second growth (Appendix: Figs. A2 and rusrufigularis)andobligateflockingspecies(e.g.,
A3). Finally, our sensitivity test, where we Thamnomanes caesius and T. ardesiacus) were
generated the same statistics using a subset of absent from true islands (Appendix: Tables A1
data with equal effort, clearly demonstrated that and A2).
differences in sampling effort did not bias our
results where islands yielded half the number of DISCUSSION
estimated species than forest fragments (Appen-
dix: Tables A3 and A4). Additionally, the DCA The succession of bird communities in second
ordination based on equal capture and point growth facilitated the recolonization of forest
count effort suggested that islands represented fragments, permitting fragments as small as 100
significantly different bird communities (Appen- ha to support bird communities similar to
dix: Figs. A4 and A5). continuous forest. Clearly, a regenerating forest
Several species intolerant to second growth matrix is not as hostile as open-water, thereby
(e.g., documented in continuous forest but never demonstratingthatislandbiogeographyisnotan
in regenerating forest) were found on true appropriate model to predict species loss in
islands: Piaya melanogaster, Celeus undatus, Tyr- forest fragments at our study site in the central
anneutes virescens, and Ramphotrigon ruficauda. Amazon. We suggest future studies use a
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Fig.6.Detrendedcorrespondenceanalysis(DCA)ordinationofcapturedata,classifiedbyforagingguildand
treatment.Asterisksrepresentsignificancelevelswhere*representsp,0.1.Numbersinparenthesesrepresent
number of species within foraging guildand total number ofindividuals captured withineach foraging guild.
countryside biogeographic framework to exam- formerly isolated fragments. In contrast, for true
ine how diverse Amazonian bird communities islands, small area coupled with the complete
perceive and use regenerating forest matrices. In absence of an adjacent second growth matrix
general, we found support for each of our four subjectedeachislandtosevereandirreconcilable
predictions used to examine the processes re- local extinction events despite the presence of
sponsible for differences in bird species richness primary forest at our study site.
and community assemblages between islands With regard to differences in diversity and
and forest fragments, and young and mature community assemblages between young and
second growth, respectively. With regard to mature regenerating forest (predictions 2 and
differences in diversity and community assem- 4), we found that bird communities varied
blages between islands and fragments (predic- significantly, when separated by guild, between
tions 1 and 3), our study demonstrated that young (15 year) and older (25 year) second
species richness in forest fragments within a growth; such differences appear to have been
regenerating matrix is not driven by extinction driven by the absence of terrestrial insectivores
dynamics as predicted by the island model. and flocking species, and the abundance of
Instead,speciesrichnessappearstobedependent nonforest species, gap-specialists and humming-
on the permeability of the surrounding matrix, birdsinyoungsecondgrowth.Ourstudyclearly
which allows recovery of bird communities in demonstrated that foraging guilds closely asso-
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